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William H. Calvin, A Brain for All Seasons:  Human Evolution and Abrupt Climate Change (University of Chicago Press, 2002), readings and notes. See also

copyright ©2002 by William H. Calvin
ISBN 0-226-09201-1 (cloth)    GN281.4 C293     
Available from or University of Chicago Press.
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This 'tree' is really a pyramidal neuron of cerebral cortex.  The axon exiting at bottom goes long distances, eventually splitting up into 10,000 small branchlets to make synapses with other brain cells.
William H. Calvin

University of Washington
Seattle WA 98195-1800 USA

Recommended Reading




For background reading on climate change in general, there are two recent books which are especially good.  Neither really explores the abrupt climate flip-flops that I focus on here, but they are exactly what you might want to give policymakers to help them sort through the more general issues of climate change.  Anyone who wishes to speak intelligently about ozone, greenhouse, and El Niño needs to read both of them. 


George H. Philander, Is the Temperature Rising?  The Uncertain Science of Global Warming (Princeton University Press 1998).  Written with grace and understatement for general readers, by someone deeply involved with modeling the climate, it covers much of a Princeton introductory course in the earth sciences.


Brian Fagan, Floods, Famines, and Emperors:  El Niño and the Fate of Civilizations  (Basic Books 1999).  See also his The Little Ice Age  (Basic Books 2000).  Archaeologists have this wonderful perspective on what’s gone wrong in the past, both with climate and human institutions.


There are two books on a more direct lineage with this one; although neither book on anthropology and climate emphasizes the abruptness aspects, they are much better on the Miocene-Pliocene climates and the slow aspects of the Pleistocene:


Steven M. Stanley, Children of the Ice Age  (Harmony 1996).  Much more on the non-abrupt aspects of anthropology and paleobiology in the ice ages.


Rick Potts, Humanity’s Descent (William Morrow 1996).  And for an excellent review of paleoclimate indicators, see his “Environmental hypotheses of hominin evolution,” Yearbook of Physical Anthropology 41:93-136 (1998).

There is now a new paleoclimate book, by one of the experts on the abruptness seen in the ice cores, that more directly addresses the present abruptness issues:

Richard B. Alley, The Two-Mile Time Machine:  Ice Cores, Abrupt Climate Change, and Our Future (Princeton University Press 2000).  It is written for nonspecialists (Alley has gotten a lot of practice as a frequent commentator for Science news articles).  The book contains far more detail on abrupt climate change than the others.  So if you find yourself asking, “But how could they possibly know that?” you’ll find most of the answers in Alley’s excellent book.  Its final chapter about the future is conventional economic extrapolation, not the more relevant perspective of high-risk management seen in medicine, re-insurance, and disaster planning.

If anyone needs a quick reference about the importance with which the scientific community views the revelations about abrupt climate change, see the Perspectives in the 15 February 2000 issue of the Proceedings of the National Academy of Sciences. In particular, see

Richard B. Alley, "Ice-core evidence of abrupt climate changes," Proceedings of the National Academy of Sciences 97(4):1331-1334 (15 February 2000) at

For a good textbook on the earth sciences, covering atmospheric sciences, geology, and oceanography, let me suggest:

Brian J. Skinner, Stephen C. Porter, Daniel B. Botkin, The Blue Planet: An Introduction to Earth Systems Science, second edition (Wiley 1999).




For the paleoanthropological side of things, there are many choices.  In general, climate makes an appearance only in its usual uplift-encouraging-the-savannas role or in the gradualist simplification of the Ice Ages.  Except within the range of tree-ring dating, events that last for only a few centuries often cannot be seen in the archaeological record because of bioturbulence smoothing the record out, and the abruptness implications of the ice cores have generally not been digested yet.  Besides Potts and Stanley, there are many other excellent books for general readers about anthropology:


Jared Diamond, Guns, Germs, and Steel: The Fates of Human Societies  (W. W. Norton 1997).  The focus is on the last 13,000 years and biogeography’s influence on domestication.

Donald Johanson, Blake Edgar, From Lucy to Language (Simon & Schuster 1996).

Richard E. Leakey, Roger Lewin,  Origins Reconsidered: In Search of What Makes Us Human  (Doubleday 1992).

 Richard E. Leakey, The Origin of Humankind (Basic Books Science Masters Series 1995).

Christopher Stringer, Robin McKie, African Exodus: The Origins of Modern Humanity (Holt 1996).

Ian Tattersall, The Fossil Trail  (Oxford University Press 1995), a history of fossil finding which has excellent fossil hominid illustrations.

Ian Tattersall, Becoming Human  (Harcourt Brace 1998). 

Ian Tattersall & Jeffrey Schwartz, Extinct Humans (Westview Press 2000).

Alan Walker and Pat Shipman, The Wisdom of the Bones (Knopf 1996).


The relevant textbooks, both of which cover hominids well, are:


John G. Fleagle, Primate Adaptation and Evolution, second edition (Academic Press 1999).  Has more of the comparative anatomy perspective of physical anthropology.

Richard G. Klein, The Human Career:  Human Biological and Cultural Origins, second edition (University of Chicago Press 1999).  Has more of the cultural perspective of archaeology.


For aspects of the great apes, start with:


Dean Falk, Primate Diversity (W. W. Norton 2000). Her book is aimed at anthropology undergraduates, with an excellent glossary.

Frans de Waal, Good Natured:  The Origins of Right and Wrong (Harvard University Press 1996).  Together with his other books for general readers, such as The Ape and the Sushi Master, Bonobo, Peacemaking Among Primates, and Chimpanzee Politics, you get a good view of what the ape-human transition might have been from.

Frans de Waal, editor, Tree of Origin:  What Primate Behavior Can Tell Us about Human Social Evolution (Harvard University Press 2001).  An excellent, readable collection of chapters by nine primatologists.




For the brain side of things, you will find many of the references in my earlier books,  The Cerebral Code, How Brains Think, Lingua ex Machina (with the linguist Derek Bickerton), and Conversations with Neil’s Brain (with the neurosurgeon George Ojemann), all at  For the connection with behavior, see:

Melvin Konner, The Tangled Wing: Biological Constraints on the Human Spirit (W. H. Freeman 2001).



Especially for evolutionary biology, some fine writers have also been at work, adding to the books written by the biologists.  It is, after all, one of the grand stories of all time – and nothing else makes much sense unless you understand the evolutionary process.



Helena Cronin, The Ant and the Peacock (Cambridge University Press 1992).

Richard Dawkins, Climbing Mount Improbable (Norton, 1996).

Daniel C. Dennett, Darwin’s Dangerous Idea (Simon & Schuster 1995).

Jonathan Miller, Darwin for Beginners (Pantheon 1982 but much reprinted) is a fine place to get up to speed, helped by the illustrations by Borin van Loon.  Called Introducing Darwin in some editions.

John Maynard Smith and Eors Szathmary, The Major Transitions in Evolution (W. H. Freeman 1995).

Ernst Mayr, This is Biology: The Science of the Living World  (Harvard University Press 1997).

Jonathan Weiner, The Beak of the Finch: A Story of Evolution in Our Time (Knopf 1994).

Christopher Wills, Understanding Evolution (W. H. Freeman 2002).

Edward O. Wilson, Consilience (Knopf, 1998).



The gradual climate change story, about the only aspect of climate change that has reached a large audience, is not covered adequately by the present book.  Few realize how strong the case is for global warming, so let me repeat here some of the items from the IPCC summary of where gradual climate change seems to be going, “Climate Change 2001:  The Scientific Basis.”

·  The global-average surface temperature has increased over the 20th century by about 0.6°C.

·  Globally, it is very likely that the 1990s was the warmest decade and 1998 the warmest year in the instrumental record, since 1861 . . . the increase in temperature in the twentieth century is likely to have been the largest of any century during the past 1000 years.

·  On average, between 1950 and 1993, night-time daily minimum air temperatures over land increased by about 0.2°C per decade.  This is about twice the rate of increase in day-time daily maximum air temperatures (0.1°C per decade).  This has lengthened the freeze-free season in many mid- and high-latitude regions.

·  Satellite data show that there are very likely to have been decreases of about 10 percent in the extent of snow cover since the late 1960s, and ground-based observations show that there is very likely to have been a reduction of about two weeks in the annual duration of lake- and river-ice cover in the mid- and high-latitudes of the Northern Hemisphere, over the twentieth century.

·  There has been a widespread retreat of mountain glaciers in non-polar regions during the twentieth century.

·  Northern Hemisphere spring and summer sea-ice extent has decreased by about 10 to 15 percent since the 1950s.  It is likely that there has been about a 40 percent decline in Arctic sea-ice thickness during late summer to early autumn in recent decades and a considerably slower decline in winter sea-ice thickness.

·  Tide-gauge data show that global-average sea level rose between 0.1 and 0.2 meters during the twentieth century.

·  It is very likely that precipitation has increased by 0.5 to 1 percent per decade in the twentieth century over most mid- and high-latitudes of the Northern Hemisphere continents, and it is likely that rainfall has increased by 0.2 to 0.3 percent per decade over the tropical (10°N to 10°S) land areas.

·  In the mid- and high-latitudes of the Northern Hemisphere over the latter half of the twentieth century, it is likely that there has been a 2 to 4 percent increase in the frequency of heavy precipitation events [thunderstorms and large-scale storm activity].

·  Warm episodes of the El Niño-Southern Oscillation (ENSO) phenomenon… have been more frequent, persistent and intense since the mid 1970s, compared with the previous 100 years.

·  In some regions, such as parts of Asia and Africa, the frequency and intensity of droughts have been observed to increase in recent decades.

·  A few areas of the globe have not warmed in recent decades, mainly over some parts of the Southern Hemisphere oceans and parts of Antarctica.

·  The atmospheric concentration of carbon dioxide has increased by 31 percent since 1750. The present CO2 concentration has not been exceeded during the past 420,000 years and likely not during the past 20 million years. The current rate of increase is unprecedent­ed during at least the past 20,000 years.

·  About three-quarters of the anthropogenic emissions of CO2 to the atmosphere during the past 20 years is due to fossil fuel burning.  The rest is predominantly due to land-use change, especially deforestation . . . .

The entire document is at


Chapter Notes

When a reference is briefly given as Author (year), it means that the full reference will be found nearby or in the Recommended Reading section.


Alley  (2000).  The several-year figure is apropos of the suddenness with which the last ice age ended about 15,000 years ago in the Northern Hemisphere, e.g., “the last ice age came to an abrupt end over a period of only three years.”  But “big changes in less than a decade” is how paleo­climatologists typically characterize all of the abrupt warmings and coolings in the best ice cores, though the full time course from one stable state to another may take a few decades.

3 Even in ordinary dry spells such as the summer of 2000, “We have the hottest driest weather in perhaps 50 years, we have thousands of lightning strikes an hour, we have 300 new fires  every day in the West, largely because of lightning strikes,’’ a senior forest service official said.  Reuters news story, 27 August 2000, datelined Boise, Idaho, USA.

3 Episodes this brief are seldom detected later by scientists studying the layers, as the worms churn the evidence, mixing up the layers from an entire millennium.  Such smoothings make it impossible to tell whether a cooling developed abruptly or more slowly, and it totally hides many of the century-long abrupt coolings and droughts, which become little bumps in the record.

4 Phoenix Generation:  Ovid didn’t describe ashes in the Assyrian version but Hans Christian Andersen added fire  in The Phoenix Bird (1872) version.

7 Jared Diamond, The Third Chimpanzee (HarperCollins 1992).

7 Besides the brain enlargement two million years ago, there was a further shift away from ape-like specializations; marathon-like endurance likely developed and childhood became even longer.  See Leakey (1995).

11            Loren Eiseley, The Night Country (Scribners 1971), p.159.  Alley (2000), p.83.


Darwin’s home 

13            Solene Morris, Louise Wilson, Down House: The Home of Charles Darwin (English Heritage 1998).  Directions to Down House can be found at­/­bookshelf/down_hse.htm

   An excellent biography in two volumes is Janet Browne’s Charles Darwin (Jonathan Cape 1995, 2002).  For Darwin’s correspondence, see

14            Dennett (1995), p.21.

16            “Swinging gait,” see Francis Darwin, “A character sketch by Darwin’s son,” pp. 88-107 in his The Life and Letters of Charles Darwin (1887).

16            There is a nice summary of the modern synthesis and punctuated equilibria in Tattersall (1998), ch. 3.

18            Repeating catastrophes:  the impact catastrophe at 65 million years ago was also a series of events and, while the extinction of the dinosaurs is one result, the adaptive radiation of mammals was another.

18            I don’t know who used the phrase first, but George Orwell wrote “Catastrophic gradualism” in the Common Wealth Review (November 1945); see Collected Essays, Journalism and Letters, vol. 4 (Harmondsworth 1978), p.35.

19            Cronin (1992), p.7.

20            Mayr (1997), p.189.


Evolution House, Kew Gardens

21            John Burnet, “Empedocles of Acragas” at

23            Darwin’s 1838 insight upon reading Thomas Robert Malthus, Essay on the Principle of Population (1798), is covered in Browne (1995) at pp.385-388.

24            A biography of Alfred Russel Wallace is at

24            Memes are discussed in Richard Dawkins, The Selfish Gene (Oxford University Press, revised edition 1989); Susan Blackmore, The Meme Machine (Oxford University Press 1999); and William H. Calvin, “The Six Essentials: Minimal Requirements for the Darwinian Bootstrapping of Quality,” Journal of Memetics 1 (1997) at

               My six essentials build on the three which Alfred Russel Wallace listed in 1875 (“. . . the known laws of variation, multiplication, and heredity . . . have probably sufficed. . . . ”); I make explicit the pattern, the work space competition, and the environmental biases.  See Wallace’s “The limits of natural selection as applied to man,” chapter 10 of Contributions to the Theory of Natural Selection (Macmillan 1875).

25            Between a third and a half of an infant’s cortical connections present at eight months of age seem to disappear by adulthood, although few neurons are lost; essentially, some axon branches are retracted.  The best data is in monkey:  P. Rakic, J.-P. Bourgeous, M. F. Eckenhoff, N. Zecevic, and P. Goldman-Rakic, “Concurrent overproduction of synapses in diverse regions of the primate cerebral cortex,” Science 232:232-234 (1986).  But the figure reflects the balance between creation of new synapses and breaking of old ones – and we don’t yet know the rate of either creation or destruction, just some estimates of the cumulative differences.  For all we know, there could be a turnover of five percent every month, with the rate of destruction only slightly greater than the rate of creation leading to the observed differences.

26            Mutations are also needed to restore variation to an inbreed population like the cheetahs who, while they might have gene-shuffling and recombination, don’t have very many alternative alleles to shuffle.



Down among the fossils

27            Why ocean bottoms remain cold, see Philander (1998), p.128.  A dramatic example of trapped CO2 bubbling out in the manner of an uncapped bottle of seltzer occurs in volcanic lakes such as Lake Nyos in the mountainous region of northwestern Cameroon, where 1,700 people were killed in 1986.  A strong wind causes the stratified lake to turn over; the gas-rich bottom waters, upon reaching the surface, release their gas in huge quantities.  In the case of Lake Nyos in 1986, the jet of gas and water shot up about 260 feet.  Moving at about 45 miles an hour, the gas reached villages 12 miles away.  The lake released about a cubic kilometer of carbon dioxide.

   It is also a sterling example of a recurring natural disaster that, now that scientists understand its mechanism, can be prevented via appropriate technology.  Michel Halbwachs, Jean-Christophe Sabroux, “Removing CO2 from Lake Nyos in Cameroon,” Science 292(5516): 438 (20 April 2001;; see the 27 February 2001 New York Times news story, “Trying to tame the roar of deadly lakes,” at

28            Flow through clouds, see Philander (1998), p.84.  For “latent heat,” see the glossary.

28            Tom Lehrer, see

31            Concealed ovulation, see Jared Diamond, Why is Sex Fun? (Basic Books 1997).

31            The C word:  William H. Calvin, “Competing for Consciousness: A Darwinian Mechanism at an Appropriate Level of Explanation,” Journal of Consciousness Studies 5(4)389-404 (1998).


   Frans de Waal, Frans Lanting,  Bonobo: The Forgotten Ape (University of California Press 1997) .  For more bonobo information, see­/bonobo.htm.


Musée de l’Homme in Paris
An excellent web starting point for paleoanthropology and its terminology is at  You can find various dates for common ancestors, depending on the method and particular genes being used.  Two recent references, with citations of other dating attempts, are:

   F. C. Chen and W. H. Li, “Genomic divergences between humans and other hominoids and the effective population size of the common ancestor of humans and chimpanzees,” American Journal of Human Genetics 68(2):444-456 (February 2001).

   S. L. Page and Morris Goodman, “Catarrhine phylogeny: Noncoding DNA evidence for a diphyletic origin of the mangabeys and for a human-chimpanzee clade,” Molecular Phylogenetics and Evolution 18(1):14-25 (January 2001).

35            Sonia Ragir, “Diet and food preparation:  Rethinking early hominid behavior,” Evolutionary Anthropology 9:153-155 (2000).

   Sonia Ragir, Martin Rosenberg, Philip Tierno, “Gut morphology and the avoidance of carrion among chimpanzees, baboons, and early hominids,” Journal of Anthropological Research 56:477-512 (2000) at

   Mark F. Teaford and Peter S. Ungar, “Diet and the evolution of the earliest human ancestors,” Proceedings of the National Academy of Sciences (U.S.) 97: 13506-13511 (5 December 2000).

   Richard W. Wrangham, James Holland Jones, Greg Laden, David Pilbeam, and NancyLou Conklin-Brittain, “The raw and the stolen: Cooking and the ecology of human origins,” Current Anthropology 40(5):567-594 (December 1999).

36            Frans B. M. de Waal, “Apes from Venus:  Bonobos and human social evolution,” in Tree of Origin, edited by Frans B. M. de Waal (Harvard University Press 2001), pp. 39-68.

36            Richard Wrangham, Dale Peterson, Demonic Males: Apes and the Origins of Human Violence (Houghton Mifflin 1996).

37            Kaye E. Reed, “Early hominid evolution and ecological change throughout the African Plio-Pleistocene.”  Journal of Human Evolution 32:289-322 (1997).  Says australopithecines are found associated with faunas suggesting wooded habitats.

37            Yves Coppens, “The East Side story,” Scientific American, pp. 88-95 (May 1994).

38            Monkeys out-competing chimps is just the latest version; there used to be lots more ape species, many more than Old World Monkeys.  But the monkeys have been gaining with the Pleistocene climate changes, showing that being smarter is not always better.  The Uganda story is from Michael P. Ghiglieri, East of the Mountains of the Moon: Chimpanzee Society in the African Rain Forest (Free Press 1988).

39            Leo Gabunia, Abesalom Vekua, David Lordkipanidze, Carl C. Swisher III, Reid Ferring, Antje Justus, Medea Nioradze, Merab Tvalchrelidze, Susan C. Antón, Gerhard Bosinski, Olaf Jöris, Marie Lumley, Givi Majsuradze, Aleksander Mouskhelishvili, “Earliest Pleistocene hominid cranial remains from Dmanisi, Republic of Georgia:  Taxonomy, geological setting, and age,” Science 288:1019-1025 (12 May 2000).

39            C. C. Swisher, W. J. Rink, S. C. Anton, H. P. Schwarcz, G. H. Curtis, A. Suprijo and Widiasmoro, “Latest Homo erectus of Java:  Potential contemporaneity with Homo sapiens in southeast Asia.” Science 274: 1870-1874 (1996).

40            The scaled-down version of the multiregional hypothesis is Milford H. Wolpoff, John Hawks, David W. Frayer, Keith Hunley, “Modern human ancestry at the peripheries: A test of the replacement theory,” Science 291:293-297 (12 January 2001).

   Yuehai Ke, Bing Su, Xiufeng Song, Daru Lu, Lifeng Chen, Hongyu Li, Chunjian Qi, Sangkot Marzuki, Ranjan Deka, Peter Underhill, Chunjie Xiao, Mark Shriver, Jeff Lell, Douglas Wallace, R Spencer Wells, Mark Seielstad, Peter Oefner, Dingliang Zhu, Jianzhong Jin, Wei Huang, Ranajit Chakraborty, Zhu Chen, and Li Jin, “African origin of modern humans in east Asia:  A tale of 12,000 Y chromosomes,” Science 292:1151-1153 (10 May 2001).  “We came to a simple conclusion,” says Li Jin. “There are no old lineages left [from archaic Asians].”

   One self-described “dedicated multiregionalist,” Vince Sarich of the University of California, Berkeley, said:  “I have undergone a conversion – a sort of epiphany.  There are no old Y chromosome lineages [in living humans].  There are no old mtDNA lineages.  Period.  It was a total replacement.”

41            Wisteria and Out of Africa, see Kenneth Kidd.

42            H. Thieme, “Lower Paleolithic hunting spears from Germany,” Nature 385:807-810 (1997).

43            Gordon H. Orians, “Human behavioral ecology:  140 years without Darwin is too long,” Bulletin of the Ecological Society of America 79(1):15-28 (1998).

43            The English landscape architects were good at keeping the large animals in the distance.  They hid a fence in a “ha-ha,” a ditch through the landscape.  From the customary viewpoint, the viewer didn’t see the ditch, looking right over the top of it at the distant pastoral landscape.

46            Category carryover from altruism to syntax:  William H. Calvin, Derek Bickerton, Lingua ex Machina:  Reconciling Darwin and Chomsky with the Human Brain (MIT Press, 2000), chapter 10.



48            Sanborn C. Brown, Benjamin Thompson, Count Rumford (MIT Press 1979).

48            Quarter-century per generation:  One sometimes sees 20 years given for the human generation time.  But a reasonable definition is not the shortest possible interval but the age of the mother at the birth of a child, averaged over her children that survive.  With menarche at 17 in Sweden only a century ago, and with the first baby having a lower chance of survival, I’d guess that the average surviving children were mostly born when the mother was between 20 and 30.

49            Richard Dawkins, The Selfish Gene (Oxford University Press 1976), p.214.

52            Jeremy R. Marlow, Carina B. Lange, Gerold Wefer, Antoni Rosell-Melé, “Upwelling intensification as part of the Pliocene-Pleistocene climate transition,” Science  290:2288-2291 (22 December 2000).

55            Leslie C. Aiello, Peter Wheeler, “The expensive tissue hypothesis:  The brain and the digestive system in human and primate evolution,” Current Anthropology 36:199-221 (1995).  And see Ann Gibbon’s news story, “Solving the brain’s energy crisis,” Science  380: 1345-1347 (29 May 1998).


Layover Limbo

59            Enlarge one neocortical area, enlarge them all” paraphrased from:  Barbara L. Finlay and R. B. Darlington, “Linked regularities in the development and evolution of mammalian brains,” Science 268:1578-1584 (1995).

59            Variation within and between species:  As my colleague Joe Felsenstein is fond of pointing out (the “coalesce fallacy”), suppose you have two species A and B.  You plot brain size vs body size for a hundred As, and perhaps you get a symmetrical scatter with no trend.  Ditto for B, except that Bs are usually bigger than As.  If you mix up As and Bs into one big scatter plot (and don’t plot the points in different colors), you get an impressive upwards trend:  “bigger bodies have bigger brains,” someone shouts - all without being able to see the trend within either species by itself.  Maybe the trend doesn’t exist at all, and is just an artifact of lumping when you should be splitting.  Actually bigger bodies within a species usually do have bigger brains, but there are many situations where lumping groups can mislead you.  Correlation is not causation, and sometimes correlation itself is – as with lumping the hypothetical As with the Bs – meaningless.  The same caution applies, say, to plotting brain size vs. IQ scores for different geographic subpopulations, e.g., races.  You need to establish the trend within the subpopulation and you constantly have to look out for a correlation which isn’t cause and effect but merely a mutual consequence of some third thing such as growth rates or hormone levels at critical periods during development.

61            I earlier discussed the r-K spectrum in chapter 6 of my The Ascent of Mind (Bantam 1990), at

   Life history analysis:  Barry Bogin, Patterns of Human Growth, 2nd ed. (Cambridge University Press 1999).

63            The data in the figure is adapted from figure 8.3 of Klein (1999), which is based on the 1990 collection of Aiello and Dean.


The Sahara

65            J. Kutzbach, G. Bonan, J. Foley, S. P. Harrison, “Vegetation and soil feedbacks on the response of the African monsoon to orbital forcing in the early to middle Holocene,” Nature 384:623-626 (19 December 1996).

   J. E. Kutzbach, Z. Liu, “Response of the African Monsoon to Orbital Forcing and Ocean Feedbacks in the Middle Holocene,” Science 278(5337) 440-443 (17 October 1997).

   Martin Claussen, Claudia Kubatzki, Victor Brovkin, Andrey Ganopolski, Philipp Hoelzmann, Hans-Joachim Pachur, “Simulation of an abrupt change in Saharan vegetation in the mid-Holocene,” Geophysical Research Letters 26(14):2037-2040 (15 July 1999).

   Philipp Hoelzmann, Birgit Keding, Hubert Berke, Stefan Kröpelin and Hans-Joachim Kruse, “Environmental change and archaeology:  Lake evolution and human occupation in the Eastern Sahara during the Holocene,” Palaeogeography, Palaeoclimatology, Palaeoecology 169:193-217 (2001).

   Ana Moreno, Jordi Targarona, Jorijntje Henderiks, Miquel Canals, Tim Freudenthal and Helge Meggers,  “Orbital forcing of dust supply to the North Canary Basin over the last 250 kyr,” Quaternary Science Reviews 20(12):1327-1339 (June 2001).

66            George Hadley, “Concerning the cause of the general trade winds,” Philosophical Transactions, vol. 39 (1735).

67            For a good explanation of the Coriolis effect, see Philander (1998), pp.95-98, 234-239.  This is why all ocean currents curve; the only one that seems to travel in a straight line for a long way is the Equatorial Undercurrent, 100 meters deep beneath the Pacific.  Being at the equator, there is no Coriolis “force” to deflect it.

68            Wallace S. Broecker, Dorothy Peteet, Irena Hajdas, Jo Lin, Elizabeth Clark, “Antiphasing between Rainfall in Africa’s Rift Valley and North America’s Great Basin,” Quaternary Research 50:12-20 (1998).

69            Stabilizing the Polar-Ferrel Cells via Gulf Stream  warming at 60°N:  This idea is surely not original to me, but I cannot  find any serious studies of its stabilizing influence, compared to other (perhaps more important) factors.

69            Philander (1998), p.153.

71               Raymond Dart, “Australopithecus africanus: the man-ape of South Africa,” Nature 115:195-199 (1925).

71               William M. Gray, John D. Sheaffer, Christopher W. Landsea, “Climate trends associated with multi-decadal variability of Atlantic hurricane activity,” pp.15-53 in Hurricanes: Climate and Socioeconomic Impacts. (H.F. Diaz and R.S. Pulwarty, eds., Springer Verlag, New York 1997).  See, p.94.

72            Chimpanzees in drier areas:  W. C. McGrew, P. J. Baldwin, C. E. G. Tutin, “Chimpanzees in a hot, dry and open habitat:  Mt. Assirik, Senegal, West Africa,” Journal of Human Evolution 10: 227-244 (1981); A. Kortlandt, “Marginal habitats of chimpanzees,” Journal of Human Evolution 12: 231-278 (1983).

   Hominids in arid environments, see Kaye E. Reed, “Early hominid evolution and ecological change through the African Plio-Pleistocene,” Journal of Human Evolution 32:289-322 (1997).


72            J. M. Diamond, Guns, Germs, and Steel: The Fates of Human Societies (Norton (1997), p.94.

72            I first discussed the “pump the periphery” principle in  The Ascent of Mind (Bantam 1990), at http:/

73            Fagan (1999), pp.168-169.

74            Stanley (1996), p.109.  The chimp subpopulation map is adapted from de Waal and Lanting (1997).


Latitude Zero

75            During glacial time (and perhaps during the cold flips as well), the tropics were less wet than now – but some desert regions such as Nevada were less dry.

77            Elisabeth S. Vrba, George H. Denton, Timothy C. Partridge, Lloyd H. Burckle (editors), Paleoclimate and Evolution, with Emphasis on Human Origins (Yale University Press 1995).

               Stephen C. Porter, “Snowline depression in the tropics during the last glaciation,” Quaternary Science Reviews  20(10):1067-1091 (2000).  Assuming a full-glacial temperature lapse rate of -6°C/1000m, depression of mean annual temperature in glaciated alpine areas was ca 5.4±0.8°C; it is similar to values of temperature depression (5-6.4°C) for the last glaciation obtained from various terrestrial sites, but contrasts with tropical sea-surface temperature estimates that are only 1-3°C cooler than present.

77            Intensification of ice sheet formation:  C. H. Haug, R. Tiedemann, “Effect of the formation of the Isthmus of Panama  on Atlantic Ocean thermohaline circulation,” Nature 393 (6686):673-676 (18 June 1998).

               K. Billups,  A. C. Ravelo, J. C. Zachos, “Early Pliocene deep water circulation in the western equatorial Atlantic: Implications for high-latitude climate change,” Paleooceanography 13: (1) 84-95 (February 1998).

80            T. C. Johnson, C. A. Sholtz, M. R. Talbot, K. Kelts, R. D. Ricketts, G. Ngobi, K. Beuning, I. Ssemmanda, J. W. McGill, “Last Plesitocene desiccation of Lake Victoria and rapid evolution of Cichlid fishes,” Science 273:1091-1093 (1996).

80            Tattersall (1995), pp. 219-220.  Richard Potts, quoted in Nature Science Update (10 May 2001).


Okavango Delta

85            Frank Almeda, “Baobabs: gnarled upside-down giants,” Pacific Discovery (Spring 1997), at

85            Mark Twain (Samuel Langhorne Clemens), Life on the Mississippi (1883), at­/twainlife/menu.html

87            Loren Eiseley, The Night Country (Scribners 1971), p.162.

87            Robert C. Walter, Richard T. Buffler, J. Henrich Bruggemann, Mireille M. M. Guillaume, Seife M. Berhe, Berhane Negassi, Yoseph Libsekal, Hai Cheng, R. Lawrence Edwards, Rudo Von Cosel, Didier Néraudeau & Mario Gagnon, “Early human occupation of the Red Sea coast of Eritrea during the last interglacial,” Nature 405(6782)65-69 (4 May 2000).  And see Chris Stringer’s comments in the same issue for shorelines more generally, together with Klein (1999), p.454.

89            The aquatic ape hypothesis (I now prefer to talk of the “shoreline foraging hypothesis” to avoid the connotation of fully aquatic) and the associated physiological agenda were reviewed at Mile 136 of my The River That Flows Uphill (Macmillan 1986), available at Physical anthropologists are unbelievably vehement in their rejection of any aquatic aspect; they talk of only “fringe groups” believing it with about the tone they otherwise reserve for those audience questions about humans evolving from space travelers, so it is not surprising that their research students stay away from the subject.

   Phillip V. Tobias, “Water and human evolution,” Out There 35: 38-44 (1998) at analyzes the savannah hypothesis and why it proved flawed, emphasizing the unanswered questions about water.

   For a neurobiological agenda that is also usually missing, see the brain developmental trajectories in Terry Deacon’s The Symbolic Species  (W. W. Norton 1997).

90            For an excellent example of how predation changes the rates of somatic growth and reproductive maturity (and makes bodies much larger and longer-lasting), see Todd A. Crowl and Alan P. Covich, “Predator-induced life-history shifts in a freshwater snail,” Science 247:949-951 (23 February 1990).  For a survey of dwarf species on the Mediterranean islands, see Paul Sondaar, “The island sweepstakes,” Natural History 95(9):50-57 (September 1986).

   During the last interglacial about 128,000 years ago, a range of hills in western Normandy was isolated by rising sea level, becoming the island of Jersey.  And within a time span of only 6,000 years (during which mainland deer didn’t change – and hadn’t for the previous 400,000 years, either), the body size of the deer inhabiting the island dropped to about one-sixth of their original size:  A. M. Lister, “Rapid dwarfing of red deer on Jersey in the last interglacial,” Nature 342:539-542 (30 November 1989).

93            Desmond Tutu, quoted in “A Tutu tribute,” South African Airways magazine (November 2000), p.30.

93            William D. Hamilton, “The genetical evolution of social behavior,” Journal of Theoretical Biology 7:1-52 (1964).

   Robert Trivers, “The evolution of reciprocal altruism,” Quarterly Review of Biology 46:35-57 (1971).

   Elliott Sober, David Sloan Wilson, Unto Others: The Evolution and Psychology of Unselfish Behavior (Harvard University Press 1998).

   Peter J. Richerson & Robert Boyd, “The Pleistocene and the origins of human culture: Built for speed,” In Perspectives in Ethology, Volume 13. Nicholas S. Thompson and Francois Tonneau, eds. (Kluwer Academic/Plenum Publishers, New York. 2000), pp. 1-45.

94            Glynn Isaac, as quoted by Leakey & Lewin (1992), p. 181.



Sossusvlei Dunes

98            The fauna associated with Australopithecine fossils indicate a wooded environment (Reed 1997, p.318); their Paranthropus successors were sometimes found in wetland environments, but it is only the later Homo species (ergaster, erectus) that are found in extremely arid and open landscape.

99            Marlow, et al (2000).  The upwelling is from a depth of about 200 m, forming filaments of cold nutrient-rich waters that extend well offshore and mix with low-productivity oceanic water, forming a zone of year-round high phytoplankton productivity.

   The figure is adapted from N. J. Shackleton, “New data on the evolution of Pliocene climatic variability,” in E. S. Vrba, G. H. Denton, T. C. Partridge, and L. H. Burckle (eds.), Paleoclimate and Evolution, With Emphasis on Human Origins (Yale University Press 1995), pp. 242-248.

100          Alan Walker and Pat Shipman, The Wisdom of the Bones (Knopf 1996), pp.89-93.



Sterkfontein Caves

103          K. Kuman and R. J. Clarke, Sterkfontein Caves: A summary of scientific research, a pamphlet available at  Sterkfontein is also nicely described by Walker and Shipman (1996), p.95.  For the World Heritage Site, see

103          The Taung endocast showing the brain surface is a natural one, made by concretelike sediments collecting on the inside of the skull long after death and settling into whatever grooves the brain surface and blood vessels had imprinted on the inside of the skull.  Latex endocasts can also be made of skulls.  For a photo gallery of skulls and endocasts, see Dean Falk’s collection at  A comparative collection of brains is at  The photograph of Tobias and Calvin is thanks to Dr. Qian Wang.

104          Ronald J. Clarke, Phillip V. Tobias, “Sterkfontein Member 2 foot bones of the oldest South African hominid,” Science 269:521-524 (28 July 1995).  And see

   Ronald J. Clarke, “First ever discovery of a well-preserved skull and associated skeleton of Australopithecus,” South African Journal of Science 94:460-464 (October 1998) at

   Ronald J. Clarke, “Discovery of the complete arm and hand of the 3.3 million-year-old Australopithecus skeleton from Sterkfontein,” South African Journal of Science 95:477-480 (November/December 1999) at

106             Growth curves in culture, see Christophe Boesch, Michael Tomasello, “Chimpanzee and human cultures,” Current Anthropology 39:591-614 (December 1998).  They introduce an unfortunate terminology for growth curve, calling it the “ratchet effect” when what they mean has no necessary aspect of backsliding prevention, only of accretion and elaboration.

   William C. McGrew, “The nature of culture:  Prospects and pitfalls of cultural primatology,” Tree of Origin:  What Primate Behavior Can Tell Us about Human Social Evolution, edited by Frans B. M. de Waal (Harvard University Press 2001), pp.231-254.

106             Henrique Teotónio, Michael R. Rose, “Variation in the reversibility of evolution,” Nature 408:463-466 (23 November 2000).

106          Tasmanian cultural losses:  see Diamond (1997), pp.312-313.

107          Richard W. Wrangham, “Out of the Pan, into the fire:  How our ancestors’ evolution depended on what they ate,” in  Tree of Origin:  What Primate Behavior Can Tell Us about Human Social Evolution, edited by Frans B. M. de Waal (Harvard University Press 2001), pp.121-143.

   Craig B. Stanford, “The ape’s gift:  Meat-eating, meat-sharing, and human evolution,” in  Tree of Origin:  What Primate Behavior Can Tell Us about Human Social Evolution, edited by Frans B. M. de Waal (Harvard University Press 2001), pp.97-117.

110             Alfred Russel Wallace, The Malay Archipelago: The Land of the Orang-utan and the Bird of Paradise; A Narrative of Travel With Studies of Man and Nature  (Macmillan 1869).


Cape of Good Hope

111          South African Museum web page (  “Tidal Fish Traps: fish traps are artificial tidal pools constructed of boulders across gullies in the intertidal zone of rocky shores.  In the recent past some were rebuilt and used by local landowners.  A number were destroyed during the construction of tidal swimming pools.  They may date back some 1600 to 2000 years when the first pastoralists reached the western Cape.”

112          Coastal caves, see Klein (1999), p. 456.

113          Louise Levathes,  When China Ruled the Seas: The Treasure Fleet of the Dragon Throne, 1405-1433  (Oxford University Press 1994).  For more, see

114          Jared Diamond, Guns, Germs, and Steel: The Fates of Human Societies  (W. W. Norton 1997).



117          See Tattersall (1995), p. 231, for a rationale for even more hominid species and genera.

   An excellent starting-point for savanna reading is Peter Matthiessen, The Tree Where Man Was Born (E. P. Dutton 1972).

119          Humans lost their “breeding season” some time ago with the advent of “concealed” ovulation (the loss of estrus behaviors which advertise optimal fertility), but similar “analog” changes are likely in many other areas capable of yielding reproductive isolation.

119          Tattersall (1998), p.103.

120          For a discussion of imprinting and its role in speciation, see P.B. Vrana, J.A. Fossella, P. Matteson, T. del Rio, M.J.O. O’Neill, S.M. Tilgham, “Genetic and epigenetic incompatibilities underlie hybrid dysgenesis in Peromyscus,” Nature Genetics 25:120-125 (2000).

120          Various studies estimate the number of unsuspected pregnancies which abort early at 13-31 percent, though in some groups (such as women who have had pelvic inflammatory disease), “early pregnancy loss” can rise to 70 percent.  So far, it seems to be the conceptions with normal karyotype whose abortion rate is increased; this isn’t just the obviously abnormal ones (trisomies, etc.).

   Five cups of coffee per day doubles the spontaneous abortion rate; see Sven Cnattingius et al., “Caffeine intake and the risk of first-trimester spontaneous abortion,” New England Journal of Medicine 343(25):1839-1845 (December 21, 2000).  Five-fold increases in spontaneous abortion are seen in some California counties if women drink the tap water rather than bottled water; see S. H. Swan et al., “A prospective study of spontaneous abortion: relation to amount and source of drinking water consumed in early pregnancy,” Epidemiology 9(2):126-133 (March 1998).  There are now a number of studies about tobacco and alcohol increasing spontaneous abortions but one must be careful to distinguish studies whose patient population has a confirmed pregnancy (seven weeks after last menses) from those “early pregnancy loss” studies using daily urine samples tested for human chorionic gonadotropin (hCG) to detect pregnancy via hCG rise in the second week after ovulation.  It is the abortion rate in the first six weeks which is so high and unexpected, a rate comparable to the induced abortion rate in many societies.

121          For the hyrax cooperation story, see Walker and Shipman (1996), pp.151-152.

122          The D2 dopamine allele story is Kenneth Blum, John G. Cull, Eric R. Braverman and David E. Comings, “Reward deficiency syndrome,” American Scientist 84(2): 132ff (March-April 1996) at

123          Richard Dawkins, Climbing Mount Improbable  (W. W. Norton, 1996), p.326.



125          A readable introduction to hominid tool use is Stanley H. Ambrose, “Paleolithic Technology and Human Evolution,” Science 291(5509)1748-1753 (2 March 2001).

126          Glynn Ll. Isaac, assisted by Barbara Isaac, Olorgesailie: Archaeological Studies of a Middle Pleistocene Lake Basin in Kenya (University of Chicago Press 1977).  And see The Archaeology of Human Origins: Papers by Glynn Isaac, Barbara Isaac (editor), pp. 289-311 (Cambridge University Press 1989).

   Richard Potts, Anna K. Behrensmeyer, Peter Ditchfield, “Paleolandscape variation and Early Pleistocene hominid activities: Members 1 and 7, Olorgesailie Formation, Kenya,” Journal of Human Evolution 37:747-788 (1999).

128          When I first saw a video of this torsional fracture technique for extracting the whitish-pink bone marrow from a fresh kill, I finally understood why the Latin prefix myelo- was used for both bone marrow and for the spinal cord.  They look alike: long, pink tubes.  Well, the fresh spinal cord has a lot of little cut nerves, once you’ve extracted it, but the resemblance to fresh bone marrow is quite striking.

129          Scavenging of contaminated meat (rather than the bone marrow and amputated legs of my examples) is perhaps best left to animals with specialized guts; see Ragir et al (2000).

130          The handaxe  drawings by C. O. Waterhouse are adapted from p.70 of Kenneth P. Oakley’s Man the Tool-maker (University of Chicago Press 1949).  The somewhat rounder Acheulian handaxe is from St. Acheul, near Amiens in the Somme.  The more elongate Acheulian handaxe is from Olorgesailie.

130          Apropos “factory site” interpretations:  The density of handaxes is not what they would have looked like in any one year, long ago.  The hard surface on which they rest was what didn’t erode, when rains washed away the mud from layers above.  So handaxes from many now-missing layers dropped their handaxes down onto the surfaces which survived the erosion (losing, of course, any vertical orientation they might have had from landing on edge).  Still, that’s a lot of lost handaxes – and this deflational surface is likely what was seen by visiting Homo erectus at various times:  an impressive display of objets trouvé.

131          Potts (1996), p.144.



133          The Rift Valley diagram is modeled after one in the National Museums of Kenya.

136          Science cover photo by R. Potts and W. Huang, showing opposing sides of a bifacially flaked large cutting tool (~803,000 years old) from the Bose Basin, South China:  Hou Yamei, Richard Potts, Yuan Baoyin, Guo Zhengtang, Alan Deino, Wang Wei, Jennifer Clark, Xie Guangmao, Huang Weiwen, “Mid-Pleistocene Acheulean-like stone technology of the Bose Basin, South China,” Science 287(5458):1622-1626 (3 March 2000).

136          Barbara Isaac, “Throwing and human evolution,” The African Archaeological Review 5:3-17 (1987).

136          Potts (1996), p.139.

137          Thomas G. Wynn, “Handaxe enigmas,” World Archaeology 27:10-23 (1995).

   Kathy D. Schick, Nicholas Toth, Making Silent Stones Speak:  Human Evolution and the Dawn of Technology (Simon & Schuster 1993).

138          Eileen M. O'Brien, “The projectile capabilities of an Acheulian handaxe  from Olorgesailie,” Current Anthropology 22:76-79 (1981).  And “What was the Acheulean hand ax?” Natural History 93:20-23 (1984).  The original idea about the handaxe being thrown may be M. D. W. Jeffreys, “The hand bolt,” Man 65:154 (1965).

   Handaxes in dried-up ponds and watercourses:  Isaac (1977); F. Clark Howell, “Isimila: A Paleolithic site in Africa,” Scientific American 205:118-129 (1961); M. R. Kleindienst and C. M. Keller, “Towards a functional analysis of handaxes and cleavers: The evidence from East Africa,” Man 11:176-187 (1976).

   Hunting per se:  Matt Cartmill, A View to a Death in the Morning (Harvard University Press 1993).

138          William H. Calvin, “The unitary hypothesis:  A common neural circuitry for novel manipulations, language, plan-ahead, and throwing?” pp. 230-250 in Tools, Language, and Cognition in Human Evolution, edited by Kathleen R. Gibson and Tim Ingold (Cambridge University Press 1993) at

140          There is one report of chimps throwing with a predatory result, see Frans X. Plooij, “Tool-use during chimpanzee's bushpig hunt,” Carnivore 1:103-106 (1978).

143          William H. Calvin, “Rediscovery and the cognitive aspects of toolmaking:  Lessons from the handaxe ,” short commentary at­/wcalvin­/2001/handaxe.htm


Lake Nakuru........................................................

149          Good introductions to climate and human evolution include Potts (1996); Stanley (1996); Reed (1997); and Stanley H. Ambrose, “Late Pleistocene human population bottlenecks, volcanic winter, and differentiation of modern humans,” Journal of Human Evolution 34(6):623-651 (1998).  For Africa more generally, see John Reader, Africa:  A biography of a continent (Knopf 1998).

149          Perhaps that’s why I like acacias so much, having studied cortical neurons for so long.  Besides the branching pattern similarities, they both have thorns (“dendritic spines”).  Indeed, “pyramidal neuron” is another misnomer (they only look triangular if their branching dendrites are invisible, as they usually were a century ago with the early microscopic techniques). 


Lake Baringo........................................................

152          Brigitte Senut, Martin Pickford, D. Gommery, P. Mein, C. Cheboi, and Yves Coppens,  “First hominid from the Miocene (Lukeino formation, Kenya),” C. R. Acad. Sci., Paris 332, 137-144 (2001), at


Lake Naivasha

159          Dirk Verschuren, Kathleen R. Laird, Brian F. Cumming, “Rainfall and drought  in equatorial East Africa during the past 1,100 years,” Nature 403:410-414 (27 January 2000).

159          “Bad times,” see J. B. Webster, in Chronology, Migration and Drought in Interlacustrine Africa (J. B. Webster, editor), pp. 1-37 (Longman & Dalhousie University Press 1979).

159          Gerard Bond, W. Showers, M. Cheseby, R. Lotti, P. Almasi, P. deMenocal, P. Priore, H. Cullen, I. Hajdas, G. Bonani, “A pervasive millennial-scale cycle in North Atlantic Holocene and glacial cycles,” Science 278:1257-1266 (1997).

160          Droughts:  Peter B. deMenocal, “Cultural responses to climate change during the late Holocene,” Science 292:667-673 (27 April 2001).  U. S. map at

   The story of the Dust Bowl drought  is at

   John Steinbeck, The Grapes of Wrath (Viking 1939), p.2.

158          Stanley H. Ambrose, “Chronology of the Later Stone Age and Food Production in East Africa ,” Journal of Archaeological Research 25(4):377-392 (1 April 1998).  “Enkapune Ya Muto rockshelter… contains the oldest known archaeological horizons spanning this transition [to the Later Stone Age]. Radiocarbon and obsidian hydration dates from this 5-6 m deep cultural sequence show that the Later Stone Age began substantially earlier than 46,000 years ago.”

160          Fidel A. Roig, Carlos Le-Quesne, José A. Boninsegna, Keith R. Briffa, Antonio Lara, Håkan Grudd, Philip D. Jones & Carolina Villagrán, “Climate variability 50,000 years ago in mid-latitude Chile as reconstructed from tree rings,” Nature 410(6828): 567-570 (29 March 2001), at

161          The self-perpetuating drought  treatment is adapted from a manuscript by my colleague John Michael Wallace, “Role of the atmosphere in abrupt climate change,” at

161          Jeffrey P. Severinghaus and Edward J. Brook, “An overview of the precise timing of atmospheric methane change relative to abrupt Greenland climate events in the past 60 ky,” American Geophysical Union fall meeting (2000).

162          Climate pumping along Silk Road route to China:  Adam Chou, “Migration of early hominids during the Pleistocene,” Journal of Human Evolution 40(3):A5 (March 2001).

163          Greenland colony:  John Gribbin, Mary Gribbin, Children of the Ice (Basil Blackwell 1980).

163          For group selection, see Sober & Wilson (1998), the special issue of American Naturalist edited by David Sloan Wilson, or his short piece, “Human groups as units of selection,” Science 276:1816-1817 (20 June 1997) at

165          Finlay & Darlington (1995).

165          William H. Calvin, “The emergence of intelligence,” Scientific American 271(4):100-107 (October 1994; also appears in Life in the Universe, 1995), at

   William H. Calvin, “A stone's throw and its launch window: Timing precision and its
implications for language and hominid brains,” Journal of Theoretical Biology 104:121-135 (1983) at  The modern version of my throwing theory is in Calvin (1993).

               William H. Calvin and Derek Bickerton, Lingua ex Machina: Reconciling Darwin and Chomsky with the Human Brain (MIT Press 2000), at

167          Nicholas Humphrey's book The Inner Eye (Faber and Faber 1986) is a good exposition on the role of social life in shaping up intelligence.

170          Frans de Waal, Good Natured:  The Origins of Right and Wrong  (Harvard University Press 1996), p.146.


Olduvai Gorge

172          James C. Woodburn, “An introduction to Hadza ecology,” in Man the Hunter, edited by Richard B. Lee and Irven DeVore (Aldine 1968) , pp. 19-55.

174          Peter Matthiessen, The Tree Where Man Was Born (E. P. Dutton 1972), pp. 285-287.

175          Science literacy, see the National Science Foundation’s report, "Science & Engineering Indicators 1998" , chapter 7, at 

          Theodosius Dobzhansky outlined the importance of evolution in the teaching of biology in an issue of The American Biology Teacher: “Seen in the light of evolution, biology is, perhaps, intellectually the most satisfying and inspiring science.  Without that light it becomes a pile of sundry facts, some of them interesting or curious but making no meaningful picture as a whole.”


Maasai Mara

180          Phillip V. Tobias, “Water and human evolution,” Out There 35: 38-44 (1998) at

180          Thure E. Cerling, “Development of grasslands and savannahs in East Africa during the Neogene,” Paleogeography, Paleoclimatology, Paleoecology 97:241-247 (1992).

181          M.J. Wooller, F.A. Street-Perrott, A.D.Q. Agnew, “Late Quaternary fires  and grassland palaeoecology of Mount Kenya, East Africa: evidence from charred grass cuticles in lake sediments,” Palaeogeography, Palaeoclimatology, Palaeoecology 164:223-246 (December 2000).

   Documenting ancient fires  is, like finding evidence for human use of fire , more difficult than it first appears.  Winds blow, worms churn, habitation sites erode from foot traffic – all serve to mix annual layers in any core except an ice or tree core.  When the diffusion process is regular, in the manner of heat within an ice sheet, deconvolution techniques can sometimes recover the original depth profile, as has been done for borehole temperatures in ice.  But even if protected pockets of sediment could be found with the potential for high temporal resolution, the issue is really such evidence on a continental scale.  Habitats are always being asynchronously disrupted by fire.  The issue for present purposes is how extensive and simultaneous a fire episode is, for which we must presently rely on the widespread and quasi-synchronous warm-and-wet and cool-and-dry associations.

182          Packrats, from Donald F. Hoffmeister, Mammals of the Grand Canyon (University of Illinois Press 1971).

185          Patricia K. Kuhl, S. Kirtani, T. Deguchi, A. Hayashi, E. B. Stevens, C. D. Dugger, and P. Iverson, “Effects of language experience on speech perception: American and Japanese infants’ perception of /ra/ and /la/,” Journal of the Acoustical Society of America 102:3135 (1997).

186             Tattersall (1998), p.102.

188          Jordi Sabater-Pi, J. J. Véa, J. Serrallonga, “Did the first hominids build nests?” Current Anthropology 38(5):914-916 (1997).

190          Amazon flow in Younger Dryas:  Mark A. Maslin and Stephen J. Burns, “Reconstruction of the Amazon Basin effective moisture availability over the past 14,000 years,” Science 290: 2285-2287 (22 December 2000).


Libya by moonlight

197          Sally McBrearty and Alison S. Brooks, “The revolution that wasn't:  A new interpretation of the origin of modern human behavior,”  Journal of Human Evolution 39 (5):453-563 (November 2000), at p.492.

197          Leakey & Lewin (1992), p.212.,p212

198          Derek Bickerton, Language and Species (University of Chicago Press 1990).

198             Leakey (1995), p.93, and Michael Balter, “New light on the oldest art,”  Science news article, 283(5404): 920-922 (12 February 1999).

199          Ian Tattersall, “The origin of the human capacity,” 68th James Arthur Lecture on the Evolution of the Human Brain, American Museum of Natural History (1998), at

200          Automaticity, see John Bargh’s work at

200          McBrearty & Brooks (2000).

201          Ganglike attacks by male chimpanzees on isolated neighbors, see Wrangham & Peterson (1996).

202          “These results indicate that male movement out of Africa first occurred around 47,000 years ago.  The age of mutation 2, at around 40,000 years ago, represents an estimate of the time of the beginning of global expansion.“  Russell Thomson, Jonathan K. Pritchard, Peidong Shen, Peter J. Oefner, and Marcus W. Feldman, “Recent common ancestry of human Y chromosomes: Evidence from DNA sequence data,” Proc. Natl. Acad. Sci. USA, Vol. 97, Issue 13, 7360-7365 (20 June 2000).

   Max Ingman, Henrik Kaessmann, Svante Pääbo, Ulf Gyllensten, “Mitochondrial genome variation and the origin of modern humans.” Nature 408:708-713 (7 December 2000).

   Ornella Semino, Giuseppe Passarino, Peter J. Oefner, Alice A. Lin, Svetlana Arbuzova, Lars E. Beckman, Giovanna De Benedictis, Paolo Francalacci, Anastasia Kouvatsi, Svetlana Limborska, Mladen Marcikia, Anna Mika, Barbara Mika, Dragan Primorac, A. Silvana Santachiara-Benerecetti, L. Luca Cavalli-Sforza, and Peter A. Underhill, “The genetic legacy of paleolithic Homo sapiens sapiens in extant Europeans:  a Y chromosome perspective,” Science 290:1155-1159 (10 November 2000).

   David Pilbeam, “Hominoid systematics: The soft evidence,” Proceedings of the National Academy of Sciences 97(20):10684-10686 (26 September 2000).

202          Early dates:  remember that recombination can severely skew the binary-branching trees we construct.  Were there some horizontal gene transfer affecting the Y chromosome or the mtDNA, it would make groups that didn’t participate look like they were the root of the tree.

203             Sahara suddenness, see references on page 330 .

206             Larry D. Agenbroad, “New World mammoth distribution,” chapter 3 of Paul S. Martin, Richard G. Klein, editors, Quaternary Extinctions (University of Arizona Press 1984), pp. 90-108.

206             Tom D. Dillehay, “The late Pleistocene cultures of South America,” Evolutionary Anthropology 7:206-216 (1999).

African skull shapes at 10,000 years ago in South America: Walter A. Neves, M. Blum, A. Prous, J. Powell, “Paleoindian skeletal remains from Santana do Riacho I, Minas Gerais, Brazil:  Archaeological background, chronological context and comparative cranial morphology,” American Journal of Physical Anthropology 114(S32):112-113 (2001).


Layover Limbo (again)

209          Fagan (2000), p.214.  Another readable account of the Little Ice Age is Thomas Levenson, Ice Times (Harper & Row 1989), chapter 4.

212          Puritans, see Jacques Barzun, From Dawn to Decadence (HarperCollins 2000), pp.277-283.

213          Little Ice Age  and witches, see Fagan (2000), p.91.

   Johann Wolfgang von Goethe, Maxims and Reflections I.

   Carl Sagan, The Demon-haunted World (Random House 1996), p.26.

214          My sketch of the Gulf Stream  and the underlying return current (the North Atlantic Deep Water) is adapted from that of Stefan Rahmstorf, “Risk of sea-change in the Atlantic,” Nature 388:825-826 (28 August 1997).


Copenhagen’s ice cores

216          There are two fine popular treatments of climate change from the 1980s that contain much useful background for today’s general reader:

   John Imbrie and Katherine P. Imbrie,  Ice Ages  (Harvard University Press 1986).

   Thomas Levenson, Ice Times:  Climate, Science, and Life on Earth (Harper & Row 1989).

   The beginning of the ice age at 2.5 million years is dated by N. J. Shackleton, J. Backman,

H. Zimmerman, D. V. Kent, M. A. Hall, D. G. Roberts, D. Schnitker, J. G. Baldauf, A. Desprairies,

R. Homrighausen, P. Huddlestun, J. B. Keene, A. J. Kaltenback, K. A. O. Krumsiek, A. C. Morton, J. W. Murray, and J. Westberg-Smith, “Oxygen isotope calibration of the onset of ice-rafting and history of glaciation in the North Atlantic region.” Nature 307:620-623 (1984). But, as would be expected from their origins in the earth's orbital cycles, the Milankovitch rhythms were present long before that, and can be seen as cycles of deep-sea anoxia: T. D. Herbert and A. G. Fischer, “Milankovitch climatic origin of mid-Cretaceous black shale rhythms in central Italy.” Nature 321:739-743 (1986). The precession and tilt (though not eccentricity) rhythms were faster, back when the moon's orbit was closer to earth: Andre Berger, M. F. Loutre, and V. Dehant, “Pre-Quaternary Milankovitch frequencies.” Nature 342:133 (1989).

   A number of candidates for a biblical deluge have since appeared, such as the waterfall when the Mediterranean poured into the Black Sea, which 7,500 years ago was a freshwater lake.  Few of the shoreline residents of the Black Sea knew anything more than that the shoreline kept moving inland, at speeds like those of a glacier surging.  See Fagan (1999), pp. 87-88.

216          Charles Darwin, “Notes on the effects produced by the ancient glaciers of Caernarvonshire, and on the boulders transported by floating ice,” Philosophical Magazine, vol. XXI (1842).  For a chronology of discoveries about the ice ages, see Imbrie & Imbrie (1986), pp.195-202.

217          Joseph Adhémar history from Wallace S. Broecker and George H. Denton, “What drives glacial cycles?”, Scientific American 262(1):48-56 (January 1990), at p. 49.  Philander (1998), pp.173-174, has one of the best explanations of the Milankovitch “orbital” factors that I have seen.  Figures adapted from Andre Berger, M. F. Loutre, H. Gallée, “Sensitivity of the LLN climate model to the astronomical and CO2 forcings over the last 200 ky,” Climate Dynamics 14:615-629 (1998).

   Peter U. Clark, Richard B. Alley, and David Pollard, “Northern Hemisphere ice-sheet influences on global climate change,” Science 286: 1104-1111 (5 November 1999).

217          Alley (2000), p.98.  Note that I am sidestepping the 100,000 year problem; the astronomy doesn’t predict a major meltoff at such intervals, and there is much speculation about exotic and terrestrial causes.  See, for example, Richard A. Muller, “Glacial cycles and orbital inclination,” Lawrence Berkeley Laboratory Report LBL-35665 (1994), available at­/www/astro­/nemesis­/LBL-35665.html.   Stochastic resonance is another possibility.

219          Discovery of Younger Dryas:  Dorothy Peteet,Sensitivity and rapidity of vegetational response to abrupt climate change,” Proceedings of the National Academy of Sciences (U.S.) 97(4):1359-1361 (15 February 2000) at

219          The temperature and precipitation records are replotted from the data of K. M. Cuffey and G. D. Clow, “Temperature, accumulation, and ice sheet elevation in Central Greenland through the last deglacial transition,” Journal of Geophysical Research 102(C12):26383-96 (1997).

221          A well-written account of Hans Oeschger ‘s study of fluctuations seen in the ice cores can be found in Thomas Levenson, Ice Times (Harper & Row 1989), chapter 3.  Thomas Stocker’s obit of Oeschger can be found at

222          The Heinrich events demonstrate that the North Atlantic may have a third mode of ocean circulation.  Today, and in the warm part of the D-O cycles, there is both far-north (above 60°N) and near-north sinking.  During the cool-and-dry part of the D-O cycle, the far-north sinking shuts down.  But during the Heinrich events, with so much fresh water being released as icebergs sail toward the Bay of Biscay, even the near-north sinking process shuts down, leaving warm water pooling in the southern oceans with no place to go.  See Alley (2000), pp.153-155.

222          Kurt M. Cuffey and Shawn J. Marshall, “Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet,” Nature 404:591-594 (2000).  The West Antarctic ice sheet contains enough water to raise sea level about 6 meters, as does Greenland; the East Antarctic ice sheet is huge in comparison, containing enough to raise sea level 60 meters.  All other glaciers in the world combined contain about 0.5 meters worth.  Both Greenland and West Antarctica have sunk enough under the weight of their ice that much of the ground beneath them is now below sea level, making them particularly vulnerable.

222          W. S. Broecker, D. Peteet, I. Hajdas, J. Lin, E. Clark, “Antiphasing between rainfall in Africa's Rift Valley and North America's Great Basin,” Quaternary Research 50:12-20 (1998).  “The beginning of the Bølling-Alleröd warm period was marked in Greenland by an abrupt rise in 18O, an abrupt drop in dust rain, and an abrupt increase in atmospheric methane content.  The surface waters in the Norwegian Sea underwent a simultaneous abrupt warming.  At about this time, a major change in the pattern of global rainfall occurred.  Lake Victoria (latitude 0°), which prior to this time was dry, was rejuvenated.  The Red Sea, which prior to this time was hypersaline, freshened.”

223          My sketch of the extent of grounded northern ice sheets is shown atop a satellite photo at modern sea levels with floating sea ice removed.  The sketch is adapted from the one in Clark et al. (1999).



The plane where it’s always noon

229          Time resolution on the scale of a year or two can be obtained from semi-fossil trees, e.g., Roig et al (2001) have a 1229-year-long stretch of tree-ring widths from the middle of the last ice age at 40°S that shows abrupt droughts with abrupt recoveries (tenfold changes in yearly accumulation), but they are floating in absolute time and such local records cannot yet be matched to events in the ice-core records.

               Tropics affected:  Konrad A. Hughen, Jonathan T. Overpeck, Scott J. Lehman, Michaele Kashgarian, John Southon, Larry C. Peterson, Richard Alley, & Daniel M. Sigman, “Deglacial changes in ocean circulation from an extended radiocarbon calibration,” Nature 391:65-68 (1 January 1998).  The figure is adapted from their figure 2 (GISP2 accumulation record and Cariaco gray scale).  And see the Cariaco Project at

   J. P. Kennett and B. L. Ingram, “A 20,000 year record of ocean circulation and climate change from the Santa Barbara Basin,” Nature 377: 510-517 (1995).

   Climate change was synchronous (within a few decades) over a region of at least hemispheric extent when rewarming from the Younger Dryas:  Jeffrey P. Severinghaus, Todd Sowers, Edward J. Brook, Richard B. Alley, & Michael L. Bender, “Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice,”  Nature 391:141-146 (8 January 1998).

229             J. A. Eddy and Hans Oeschger, editors, Global Changes in the Perspective of the Past (Wiley 1993).

   “Broecker, too, heard Oeschger that year”:  see Wallace S. Broecker, “Will our ride into the greenhouse future be a smooth one?”  GSA Today 7(5):1-7 (May 1997).  For more autobiography, see his “Converging paths leading to the role of oceans in climate change,” Annual Reviews of Energy and Environment 25:1-19 (2000).

229          Droughts, see Fagan (1999), p.87.

230          “Relative stability” means avoiding the centuries-duration scale of D-O events of 5-15°C, though that leaves a lot of room for more minor fluctuations such as the 1,500-year cycle and the decade-scale rhythms that are now being studied.  For some contrasts between the Younger Dryas and the most serious droughts since then at 8200, 5200, and 4200 years ago, see Fagan (1999) and Harvey Weiss,  “Beyond the Younger Dryas:  Collapse as adaptation to abrupt climate change in ancient West Asia and the Eastern Mediterranean,” pp. 75-98 in Confronting Natural Disaster: Engaging the Past to Understand the Future, G. Bawden and R. Reycraft, editors (University of New Mexico Press 2000), at

229          M. E. Raymo, K. Ganley, S. Carter, D. W. Oppo, & J. McManus, “Millennial-scale climate instability during the early Pleistocene epoch,”  Nature 392:699-702 (16 April 1998).

230          At is most of the North GRIP project information, and the earlier data is available at 

230          P. E. Biscaye, F. E. Grousset, M. Revel, S. VanderGaast, G. A. Zielinski, A. Vaars, and G. Kukla, “Asian provenance of glacial dust (stage2) in the Greenland Ice Sheet Project 2 Ice Core, Summit, Greenland,” Journal of Geophysical Research 102:765-781 (1997).  Carbon dioxide is best studied in bubbles from Antarctic cores, where the ice is fewer potential contaminants than ice from Greenland; in general, see Alley (2000), p.103.

232             Pieter M. Grootes, M. Stuiver, J. W. C. White, S. Johnsen, and J. Jouzel, “Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores,” Nature 366:552-554 (1993).

   Willi Dansgaard, S. J. Johnsen, H. B. Clausen, D. Dahl-Jensen, N. S. Gundestrup, C. U. Hammer, C. S. Hvidberg, J. P. Steffensen, A. E. Sveinbjörnsdottir, J. Jouzel, G. Bond,  “Evidence for general instability of past climate from a 250 kyr ice core,” Nature 364:218-219 (1993). 

   Figure adapted from J.R. Petit, J. Jouzel, D. Raynaud, N.I. Barkov, J.-M. Barnola, I. Basile, M. Bender, J. Chappellaz, M. Davis, G. Delayque, M. Delmotte, V.M. Kotlyakov, M. Legrand, V.Y. Lipenkov, C. Lorius, L. Pépin, C. Ritz, E. Saltzman, and M. Stievenard, “Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica,” Nature 399:429-436 (1999).

234          Laurie Anderson, “Same time tomorrow” lyrics, Bright Red, track 14 (Time Warner 1994).


High above Oslo.................................................

236          Leonid Polyak, Margo H. Edwards, Bernard J. Coakley, Martin Jakobsson, “Ice shelves in the Pleistocene Arctic Ocean inferred from glaciogenic deep-sea bedforms,” Nature 410:453-457 (22 March 2001).  Bottom scouring at 1000 m depths; icebergs in the Arctic Ocean have at most 50-m draughts, whereas icebergs off Antarctica and Greenland reach depths of 550 m.

238          The reason I say “habitable world appears to be chilled” is that some areas of the South Pacific and Atlantic Oceans, and some (but not all) parts of Antarctica, may be exceptions.  The extent of the Younger Dryas in higher southern latitudes may be somewhat spotty, as it is superimposed on the warming trend after the last glacial maximum which began in the south and spread north.  See K. D. Bennett, S. G. Haberle, and S. H. Lumley,  “The Last Glacial-Holocene transition in southern Chile,” Science 290:325-328 (13 October 2000),  and the perspective at pp.285-286.

238          Wallace S. Broecker, “Chaotic climate,” Scientific American 273(5):62-69 (November 1995).  A hundred Amazons is Broecker’s figure; if the Amazon flow is instead taken as 0.19 Sv, and the southbound NADW off Newfound­land as 13 Sv, then it is more like 70 Amazons.  But deep water production by convection may be less, depending on how much NADW is Arctic in origin and how much is simply recirculated Antarctic bottom water (extremely dense water, formed as brine under the sea ice around polynas offshore of Antarctica and sliding down the continental shelf into the depths without much mixing, creates a giant pool of dense water extending all the way up the bottom of the Atlantic to about 60°N).  Greenland Sea production is said to be 5.6 Sv, about equally divided between the sills to the east and west of Iceland.  Labrador Sea production is difficult to estimate because of the local gyre and the frequent annual failures.

239          Robert Bindschadler, “Future of the West Antarctic Ice Sheet,” Science 282:428-429 (16 October 1998).

239          G. H. Denton, C. H. Hendy, “Younger Dryas Age Advance of Franz Josef Glacier in the Southern Alps of New Zealand,” Science 264:1434-1437 (3 June 1994; follow up at 271:668-669, 2 February 1996).

   Judith Lean and David Rind, “Earth's Response to a Variable Sun,” Science 292(5515) 234-236 (13 April 2001).

   Peter V. Foukal, “The variable sun,” Scientific American 262(2):34-41 (February 1990). 

   U. Neff, S. J. Burns, A. Mangini, M. Mudelsee, D. Fleitmann & A. Matter, “Strong coherence between solar variability and the monsoon in Oman between 9 and 6 kyr ago,” Nature 411:290-293 (2001).

   J. D. Haigh, “The impact of solar variability on climate,” Science 272:981-984 (1996).

   Reductions in solar output might, of course, be one of the things that set the stage for an abrupt cooling, as might the North Atlantic Oscillation and other atmospheric cycles like El Niño.  Causes usually don’t come one at a time, but combine in various ways.

   For climate variability more generally, start at the CLIVAR web pages at

242          Alley (2000), p.3.


Out over the sinking Gulf Stream

245          Henry M. Stommel, “Thermohaline convection with two stable regimes of flow,” Tellus 13:224-230 (1961) had the concept of freshening of surface waters interfering with the thermohaline sinking.  The conceptual map is from Stommel (1957), see

246          Wallace S. Broecker, “The great ocean conveyor ,” Oceanography 4:79-89 (1991).

   Wallace S. Broecker, "Abrupt climate change: causal constraints provided by the paleoclimate record," Earth-Science Reviews 51:137-154 (August 2000).

   D. J. Webb and N. Suginohara, “Oceanography: Vertical mixing in the ocean,” Nature 409:37 (4 January 2001).

248          Broecker (1997), p.1.


Jan Mayen Island

249          Walter Munk, Laurence Armi, Kenneth Fischer, F. Zachariasen, “Spirals on the sea,” Proceedings of the Royal Society: Mathematical, Physical & Engineering Sciences 456:1217-1280 (1997).  First seen in the Apollo missions of the 1960s, spirals are broadly distributed over the world's oceans, 10-25 km in size and overwhelmingly cyclonic.

   Whirlpools associated with salt play an interesting role in Norse legends.  See chapter 6 of Giorgio de Santillana and Hertha von Dechend, Hamlet’s Mill: An Essay Investigating the Origins of Human Knowledge and its Transmission Through Myth (Godine 1969).

250          Alexander Sy, Monika Rhein, John R. N. Lazier, Klaus Peter Koltermann, Jens Meincke, Alfred Putzka, and Manfred Bersch, “Surprisingly rapid spreading of newly formed intermediate waters across the North Atlantic Ocean,” Nature 386:675-679 (17 April 1997).

250          Michael S. McCartney, Ruth G. Curry, Hugo F. Bezdek, “North Atlantic transformation pipeline chills and redistributes subtropical water,” Oceanus 39(2):19-23 (Fall/winter 1996).  This article elaborates on the multi-year aspects of the formation of salt sinking in the sub-polar gyre.


The Greenland Sea

254          Switching from Greenland to Labrador domination:  R. Dickson, J. Lazier, J. Meincke, P. Rhines, J. Swift, “Long-term coordinated changes in the convective activity of the North Atlantic,” Progress in Oceanography 38:241-295 (1996).

254             G. C. Bond, R. Lotti, “Iceberg discharges into the North Atlantic on millennial time scales during the last glaciation,” Science 267:1005 (17 February 1995).

   Wallace S. Broecker, “Massive iceberg discharges as triggers for global climate change,” Nature 372:421-424 (1994).

255          Date for closure of “Old Panama  Canal”:  Neil D. Opdyke, “Mammalian migration and climate over the last seven million years,” chapter 8 in Paleoclimate and Evolution, with Emphasis on Human Origins, edited by Elisabeth S. Vrba, George H. Denton, Timothy C. Partridge, Lloyd H. Burckle (Yale University Press 1995), pp.109-114 at p.112.

256          C. H. Haug, R. Tiedemann, “Effect of the formation of the Isthmus of Panama  on Atlantic Ocean thermohaline circulation,” Nature 393(6686):673-676 (18 June 1998).

   There is a similar theory for how African climate was affected by New Guinea moving northward to close off the easy circulation between Pacific and Indian Oceans:  Mark A. Cane, Peter Molnar,  “Closing of the Indonesian seaway as a precursor to east African aridification around 3–4 million years ago,” Nature 411:157-162 (10 May 2001).

260          Photograph of Greenland mountain peaks exposed by the thinning continental ice sheet:  Rock protruding through an ice sheet is called a nunatak.  The low light angle is from the midnight sun, as the picture was taken looking south on an eastbound flight in the summer in the early morning hours.


Greenland fjords.................................................

261             Peter Schlosser, Gerhard Bönisch, Monika Rhein, Reinhold Bayer, “Reduction of deepwater formation in the Greenland Sea during the 1980s:  Evidence from tracer data,” Science 251:1054-1056 (1 March 1991).

   Gerhard Bönisch, Johan Blindheim, John L. Bullister, Peter  Schlosser, and Douglas W. R. Wallace, “Long term trends of temperature, salinity,  density, and transient tracers in the Central Greenland Sea,” Journal of Geophysical Research 102:18553-18571 (1997), see

261          Michael S. McCartney, “North Atlantic Oscillation,” Oceanus 39(2):13 (Fall/winter 1996).  The regional atmospheric circulation over the North Atlantic normally features a high over the Azores and a low near Greenland and Iceland – the westerlies are intense but the cold air from Canada is warmed before reaching Europe.  When the low shifts as far south as Newfoundland, a high develops over northern Greenland; this brings cold arctic air west from northern Europe to be warmed by the Norwegian Current and thus warm Greenland and North America rather than Europe.  The Labrador Sea is much less stormy and this likely affects salt sinking.

The NAO is best understood as a ring of pressure anomalies extending around the globe, not just a North Atlantic phenomenon (something similar happens in the Southern Hemisphere at similar latitudes).  See Dennis L. Hartmann, John M. Wallace, Varavut Limpasuvan, David W. J. Thompson, and James R. Holton, “Can ozone depletion and global warming interact to produce rapid climate change?” Proceedings of the National Academy of Sciences (U.S.) 97:1412-1417 (15 February 2000) at

               The relationships between the NAO and deep water production are discussed by R. Dickson, “Observations of DecCen climate variability in convection and water mass formation in the northern hemisphere,” in the CLIVAR Villefranche workshop summary at  More generally, see the Climate Research Committee, National Research Council,  Natural Climate Variability on Decade-to-Century Time Scales (National Academy Press 1995).  Excerpts can be found at 

262          Sinking to the very bottom may be important for the return leg of the trip, south past the coast of Newfoundland where it must stay beneath the Gulf Stream .  There is some speculation that it sometimes doesn’t, and is swept eastward, illustrating a mechanism for creating blobs that recirculate.  It is known that semi-salty, or anomalously warm or cool, blobs even travel from the subtropics, up and around the Greenland Seas and back around to the Labrador Sea, suggesting another failure mode for late winter downwelling; see Raymond W. Schmitt, “If rain falls on the ocean, does it make a sound?”  Oceanus 39(2):4-8 (Fall/winter 1996).

263          Thomas F. Stocker, Olivier Marchal, “Abrupt climate change in the computer: Is it real?” Proceedings of the National Academy of Sciences (U.S.) 97:1362-1365 (15 February 2000) at

   Andrey Ganopolski and Stefan Rahmstorf, “Simulation of rapid glacial climate changes in a coupled climate model,” Nature 409:153-158 (11 January 2001) at

263          Bogi Hansen, William R. Turrell, Svein Østerhus, “Decreasing overflow from the Nordic seas into the Atlantic Ocean through the Faroe Bank channel since 1950,” Nature 411:927-930 (21 June 2001).


Atop Greenland...................................................

266             For the hinge from which icebergs break off, see E. J. Rignot,  S. P. Gogineni, W. B. Krabill, S. Ekholm, “North and northeast Greenland ice discharge from satellite radar interferometry,” Science 276:934-937 (9 May 1997).

   Sometimes glaciers surge a mile a month (the Bering glacier east of Cordova, Alaska – North America’s longest glacier – is currently surging), but that’s because of warming, not cooling.  Another one of the ice paradoxes is that glaciers can advance for either reason.  Glaciers, too, have modes of operation:  once melting starts, a mountain of ice tends to collapse, spreading sideways.  Because meltwater runs off beneath the glacier (and can form there from all the trapped heat from the earth), it smoothes the undersurface and greases the skids.  The glacial snout may advance so quickly that the ocean’s chipping away at it cannot keep up.  And so the snout of the glacier pushes further into the sea over a course of months.  Eventually the tides may break it loose.

266          William S. Reeburgh, D. L. Nebert, “The birth and death of Russell Lake,” Alaska Science Forum 832 (3 August 1987) at See also

267          R. B. Alley, P. A. Mayewski, T. Sowers, K. C. Taylor, and P. U. Clark, "Holocene climatic instability: A prominent, widespread event 8200 yr ago." Geology 25:483-486 (1997).

   D. C. Barber, A. Dyke, C. Hillaire-Marcel, A. E. Jennings, J. T. Andrews, M. W. Kerwin, G. Bilodeau, R. Mcneely, J. Southon, M. D. Morehead & J.-M. Gagnon, “Forcing of the cold event of 8,200 years ago by catastrophic drainage of Laurentide lakes,” Nature 400:344-348 (1999).

268          Richard A. Kerr, “Warming's unpleasant surprise: Shivering in the greenhouse?” Science 281:156-158 (news article, 10 July 1998).



270          An even longer record comes from the high tropics, going back about 500,000 years and showing many abrupt temperature changes.  L. G. Thompson, T. Yao, M. E. Davis, K. A. Henderson, E. Mosley-Thompson, P.-N. Lin, J. Beer, H.-A. Synal, J. Cole-Dai, J. F. Bolzan, “Tropical climate instability: The last glacial cycle from a Qinghai-Tibetan ice core,” Science 276:1821-1825 (20 June 1997) at

270             Mark Maslin, “Sultry last interglacial gets a sudden chill,” Earth in Space 9(7):12-14 (March 1997) at  One of the current uncertainties about the mid-Eemian cooling event at 122,000 years is whether it involved the complete shutdown of the North Atlantic Deep Water production; various ocean-floor cores suggest it didn’t.

L. D. Keigwin, W. B. Curry, S. J. Lehman, S. Johnsen, “The role of the deep ocean in North Atlantic climate change between 70 and 130 kyr ago,” Nature 371:323-326 (22 September 1994).

   J. F. McManus, G. C. Bond, W. S. Broecker, S. Johnsen, L. Labeyrie, S. Higgins, “High-resolution climate records from the North Atlantic during the last interglacial,” Nature 371:326-329 (22 September 1994).

   Robert R. Dickson, “The local, regional, and global significance of exchanges through the Denmark Strait and Irminger Sea,” in Natural Climate Variability of Decade-to-Century Time Scales (National Academy Press 1995), pp. 305-317.

   R. R. Dickson, J. Meincke, S-A. Malmberg, and A. J. Lee, “The `great salinity anomaly’ in the northern North Atlantic 1968-1982,” Progress in Oceanography 20:103-151 (1988).  Note that the Great Salinity Anomaly, equivalent to an extra 2,000 km3 of fresh water, is not usually treated as a fjord flood but as a variant on a semi-salty current out of the Arctic Sea.  This volume is about 500 times the freshwater flux from Alaska’s Russell Fjord over a five-month period – but then the reservoir capacity of the east Greenland fjord system at 70-77°N is also extraordinary and ice dams can span multiple years.  The travel time from the Labrador Sea to Bermuda is about six years.

272          Hard to restart:  it’s an example of hysteresis.  This is one of those asymmetric situations where it is easy to get in but hard to get out, something like a one-way street where you can’t turn around but are forced to go all the way around the block instead.  See the diagram in Stocker & Marchal (2000).

273          Albedo argument for 1,500-year cycle:  Here I am paraphrasing from a lecture at the University of Washington by Wally Broecker (12 December 2000), “The big amplifier– bipolar seesaw tie.”

   Note also that desert dust inhibits precipitation by a mechanism that increases albedo:  Daniel Rosenfeld, Yinon Rudich,, and Ronen Lahav, “Desert dust suppressing precipitation: A possible desertification feedback loop,” Proc. Natl. Acad. Sci. USA 98(11):5975-5980 (22 May 2001).

276             Ray T. Pierrehumbert, “Climate change and the tropical Pacific: The sleeping dragon wakes,”  Proceedings of the National Academy of Sciences (U.S.) 97:1355-1358 (10 February 2000) at

263          Thomas Levenson, Ice Times (Harper & Row 1989), p.49. 


Somerset Island

277          For more on why open ocean occurs occasionally in Arctic summers, sometimes even at the pole itself, see  There is an enormous heat flux through them, as the difference between surface and air temperature is 30°C.  They soon refreeze (unless they are maintained open by offshore winds, as in Antarctica) and produce a layer of brine.

   News article by John Noble Wilford, “Ages-old polar icecap is melting, scientists find,” New York Times (August 19, 2000), at  Actually, none of the Arctic sea ice is much over three years old, and that at 90°N is usually only a year old.  The more common confusion is between an ice sheet, which can be 3,000 meters thick, and floating sea ice (in the Arctic, seldom more than 3 meters thick).  The Antarctic is a continent surrounded by ocean; the Arctic is a nearly landlocked sea surrounded by continents which empty fresh water into it via north-flowing rivers; using the same word, “icecap,” for both is misleading, however correct.

278          D. A. Rothrock, Y. Yu, G. A. Maykut, “Thinning of sea-ice cover,” Geophysical Research Letters 26:3469-3472 (1 December 1999).

   Ola M. Johannessen, Elena V. Shalina, Martin W. Miles, “Satellite evidence for an Arctic sea ice cover in transformation,” Science 286:1937-1939 (3 December 1999).

   Konstantin Y. Vinnikov, Alan Robock, Ronald J. Stouffer, John E. Walsh, Claire L. Parkinson, Donald J. Cavalieri, John F. B. Mitchell, Donald Garrett, Victor F. Zakharov, “Global warming and Northern Hemisphere sea ice extent,” Science 286:1934-1937 (3 December 1999).  And see the follow up at  Science 288:927 (2000).

278          The special pleading works much better with real juries, from which knowledgeable jurors have been systematically excluded, than it does with the general public.  Anyone who knows more about the science or technology than the lawyers is usually rejected during jury selection.  And the judges allow it.

278          Instrumental record:  J. Fred Singer, “Global warming: An insignificant trend?” Science 292:1063 (2001).  And see Donald Kennedy’s pointed reply which follows it.

279          Abrupt change from wet to dry in the Sahara  (at least, as measured by offshore dust) as the axial tilt gradually changes:  Peter B. deMenocal, J. Ortiz, T. Guilderson, J. Adkins, M. Sarnthein, L. Baker, and M. Yarusinsky, “Abrupt onset and termination of the African Humid Period:  Rapid climate responses to gradual insolation forcing,” Quaternary Science Review 19: 347-361 (2000).

280          Though I cannot find any literature on equatorial warming triggering reorganization for the D-O events, there are reports, for the glacial-interglacial transition, that Pacific sea surface temperatures warmed 3,000 years before changes in ice volumes.  See David W. Lea, Dorothy K. Pak, and Howard J. Spero, “Climate impact of Late Quaternary equatorial Pacific sea surface,” Science 289:1719 (8 September 2000) at

280          Quote from Broecker (1997), p. 5.  Quote from Alley (2000), p. 83.

282          Philander (1999), p.3.


Crossing the North American coast

286          Apropos the comparison of Canada to Europe, Conway Leovy reminds me that Europe does not have an equivalent of the rain shadow from the Rockies.

289          Edward O. Wilson, Consilience: Unity of Knowledge (Knopf 1998), p.13.

290          Weiner (1994), p.286.



Yellowknife, Northwest Territory

291          Canadian warming: K. E. Taylor, J. E. Penner, “Response of the climate system to atmospheric aerosols and greenhouse gases,” Nature 369:734-737 (1994).

291          The idea of a Precambrian glaciation covering even the tropics goes back to the 1960s but it was dismissed, despite the evidence of glacial till in suspicious places, overlain by tropical sediments.  Essentially, should the sun’s output reaching the earth decline a few percent (Sun itself, dust clouds, whatever), even the tropics freeze and the albedo keeps it that way.  The idea was revived in the 1990s because of a mechanism (volcanic CO2 becoming 10% of air) that would melt it back within a few million years, after which there is a Hothouse Earth for a few million years until the thirty-fold-greater CO2 is removed from the atmosphere.  At least two such episodes are thought to have occurred between 750 and 550 million years ago.

   Paul F. Hoffman, Alan J. Kaufman, Galen P. Halverson, and Daniel P. Schrag, “A neoproterozoic snowball earth,” Science 281(5381):1342-1346 (28 August 1998).

               Paul F. Hoffman, Daniel P. Schrag, “Snowball Earth,” Scientific American, pp. 68-75 (January 2000) at

292          Weathering feedback, see Alley (2000), p.86.

293          Robert J. Charlson, James E. Lovelock, Meinrat O. Andreae, Stephen G. Warren, “Oceanic phytoplankton, atmospheric sulphur, cloud albedo, and climate.”  Nature 326:655-661 (1987).

295          W. H. Calvin, C. F. Stevens, “A Markoff process model for neuron behavior in the interspike interval,” Proceedings of the Annual Conference on Engineering in Medicine and Biology 7:118 (1965).



Bumpy border crossing

296          Lewis Thomas, Late Night Thoughts on Listening to Mahler's Ninth Symphony, (Viking 1983), p. 15.

297          Robert Burns, The Shape and Form of Puget Sound (University of Washington Press 1985), p. 43.

297             Michael Parfit, “Before Noah, there were the Lake Missoula Floods,” Smithsonian (April 1995).

   John Eliot Allen and Marjorie Burns, Cataclysms on the Columbia (Portland: Timber Press 1986).

298          See Antonio Damasio, The Feeling of What Happens  (1999).  “Consciousness and its revelations allow us to create a better life… but the price we pay for that better life is high. It is not just the price of risk and danger and pain. It is the price of knowing risk, danger, and pain.  Worse even: it is the price of knowing what pleasure is and knowing when it is missing or unattainable.” [p.316]



305          William H. Calvin, “The great climate flip-flop,” The Atlantic Monthly  281(1):47-64 (January 1998) at

The underreporting of abrupt climate change persisted from 1985 to 1998, even in the face of substantial recognition of some of the major players.  For example, Wallace S. Broecker – easily the most vigorous of the geoscientists in trying to alert the scientific community, and author of several Scientific American articles – was awarded the U.S. National Medal of Science by President Clinton in 1996 for “contributions to understanding chemical changes in the ocean and atmosphere.”  (  The Danish ice-core expert Willi Dansgaard and the British oceanographer Nicholas Shackleton received the Crafoord Prize from the Swedish Academy in 1995 (see  Dansgaard, the Swiss climatologist Hans Oeschger, and the French climatologist Claude Lorius received the $150,000 Tyler Prize in 1996.

Yet, despite all this recognition and all those news stories in Science and Nature,  the bistable climate story itself (sudden warmings, flipping to sudden coolings) was seldom reported in the popular press.  It was conflated with other rapid climate changes (volcanoes, ice shelves breaking up) lacking bistable states, or it was simply lost in a greenhouse story.  It would be interesting for some student of the media to sort out the underlying reasons why such a major story was ignored.

An exception was Ross Gelbspan, The Heat Is On (Addison-Wesley 1997), who treats the abrupt cooling story at pp. 28-31.

“Anthropogenic warming” is a classic example of how not to frame an issue.  It hurts no matter what caused it; assigning fault doesn’t resolve anything in this case.  And just because something is “natural” doesn’t mean it is out of our control.  (Floods?  Smallpox?)  Many of the people whose pockets might be hurt by expenses for combating warming are quite happy to see the issues dumped solely into the laps of the scientists, perhaps because they know that scientific studies always raise more questions than they answer, and so the issue of whether science has spoken on the issue can be indefinitely postponed.  Public policy has some similarities to medicine; the physician who waits until dead certain of a diagnosis before starting treatment may often wind up with a dead patient.  Often, one cannot wait for scientific certainty.



317          Peter Schuster, “Molecular insights into life and evolution,” the 1998 Schrödinger lecture, at  Trinity College Dublin,

Copyright ©2002 by
William H. Calvin

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A Brain for All Seasons, 2002

Conversations with Neil's Brain:  The Neural Nature of Thought and Language (Calvin & Ojemann, 1994)

The Cerebral Code:  Thinking a Thought in the Mosaics of the Mind (1996)

How Brains Think:  Evolving Intelligence, Then and Now (1996)

Lingua ex Machina:  Reconciling Darwin and Chomsky with the Human Brain (Calvin & Bickerton, 2000)

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Inside the Brain

The Throwing Madonna:  Essays on the Brain

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How the Shaman Stole the Moon