W. H. Calvin's THE ASCENT OF MIND (Notes and Bibliography)
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A book by
William H. Calvin
The Ascent of Mind (Bantam 1990) is my book on the ice ages and how human intelligence evolved; the "throwing theory" is one aspect.
   My Scientific American article, "The emergence of intelligence," (October 1994) also discusses ice-age evolution of intelligence. Also see Wallace S. Broecker, "Massive iceberg discharges as triggers for global climate change," Nature 372:421-424 (1 December 1994) and his "Chaotic Climate" Scientific American article (November 1995 issue).
AVAILABILITY is challenging.
Many libraries have it (try the OCLC on-line listing), but otherwise it’s strictly used bookstores (and German and Dutch translations).
The Ascent of Mind
Ice Age Climates and
the Evolution of Intelligence

Copyright ©1990 by William H. Calvin.

You may download this for personal reading but may not redistribute or archive without permission (exception: teachers should feel free to print out a chapter and photocopy it for students).


Chapter 1. Following the Gulf Stream to Europe:
Tracking Climate Change and Human Evolution

1994 Update: The current dating of the Younger Dryas onset is 13,000 years ago rather than the 11,500 mentioned in this 1990 manuscript. And the abrupt climate changes are even more frequent than then appeared: see Wallace S. Broecker, "Massive iceberg discharges as triggers for global climate change." Nature 372:421-424 (1 December 1994). For updates on El Nino, see El Nino tuitorial from NOAA.

2 Robert Ardrey, The Hunting Hypothesis (Atheneum, 1976).

4 Lionel E. Jackson, Jr. and Alejandra Duk-Rodkin, "Geology of the ice-free corridor." University of Washington lecture (19 January 1988). E. James Dixon, "Eastern Beringian paleoindians and the paleoenvironments of the ice-free corridor." University of Washington lecture (1 March 1988). Michael Wendorf, "Diabetes, the ice free corridor, and the paleoindian settlement of North America." American Journal of Physical Anthropology 79(4):503-520 (1989). Joseph H. Greenberg, Christy G. Turner II, and Stephen L. Zegura, "The settlement of the Americas: A Comparison of the linguistic, dental, and genetic evidence." Current Anthropology 27(5):477-497 (1986).

6 For the general anthropological background concerning ice-age Europe, see John Gowlett, Ascent to Civilization: The Archaeology of Early Man (Knopf, 1984). For the general background on the ice-age theories, see John Imbrie and Katherine P. Imbrie, Ice Ages (Harvard University Press, 1986); John Gribbin and Mary Gribbin, Children of the Ice: Climate and Human Origins (Basil Blackwell, 1990); and Wallace S. Broecker and George H. Denton, "What drives glacial cycles?" Scientific American 262(1):48-56 (January 1990). For the greenhouse, see Warren M. Washington, "Where's the heat?" Natural History (3):66-72 (1990).

7 Initially, several layers of Dryas pollen showed up in Denmark, but only the more recent of them was seen elsewhere, hence the "Younger Dryas" terminology that is conventional for this period. From a lecture by Dorothy M. Peteet, "Younger Dryas oscillation: a late-glacial example of abrupt climatic change," University of Washington (28 February 1989).

The basic data on the cold spikes is in: W. Dansgaard, H. B. Clausen, N. Gundestrup, C. U. Hammer, S. F. Johnsen, P. M. Kristinsdottir, and N. Reeh, "A new Greenland deep ice core." Science 218:1273-1277 (1982). For droughts, see F. Alayne Street-Perrott and R. Ross Perrott, "Abrupt climate fluctuations in the tropics: the influence of Atlantic Ocean circulation." Nature 343:607-612 (15 February 1990). For what droughts did in the U.S. Southwest, see Robert C. Euler, George J. Gumerman, Thor N. V. Karlstrom, Jeffrey S. Dean, and Richard H. Hevly, "The Colorado plateau: Cultural dynamics and paleoenvironment." Science 205:1089-1101 (14 September 1979).

The timing of the termination of the Dryas at about 10,700 years ago is in W. Dansgaard, J. W. C. White, and S. J. Johnsen, "The abrupt termination of the Younger Dryas climate event." Nature 339:532-534 (15 June 1989).

The basics on the carbon budget of the earth can be found in Richard A. Houghton and George M. Woodwell, "Global climatic change." Scientific American 260(4):36-44 (April 1989).

David A. Peel, "Ice-age clues for warmer world." Nature 339:508-509 (15 June 1989).

Wallace S. Broecker, Dorothy M. Peteet, and David Rind, "Does the ocean-atmosphere system have more than one stable mode of operation." Nature 315:21-26 (2 May 1985). Wallace S. Broecker, "Unpleasant surprises in the greenhouse?" Nature 328:123-126 (9 June 1987). And Broecker et al, "The chronology of the deglaciation: Implications to the cause of the Younger Dryas cooling." Paleoceanography 3:1-19 (1988). Richard G. Fairbanks, "A 17,000-year glacio-eustatic sea level record: Influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation." Nature 342:637-642 (7 December 1989). E. Jansen and T. Veum, "Evidence for two-step deglaciation and its impact on North Atlantic deep-water circulation." Nature 343:612-616 (15 February 1990). Hans Oeschger and C. C. Langway, editors, "The Environmental Record in Glaciers and Ice Sheets." Dahlem Workshop 8 (Wiley, 1989). Hans Oeschger and H. U. Dütsch, "Ozone and the Greenhouse Effect." Nature 339:19 (4 May 1989). Robert J. Charlson, James E. Lovelock, Meinrat O. Andreae, and Stephen G. Warren, "Oceanic phytoplankton, atmospheric sulphur, cloud albedo, and climate." Nature 326:655-661 (1987). And the news stories regarding cloud cover and albedo, "Pinning down clouds" in Scientific American 260(5):22-24 (May 1989) and "Cloudy concerns" in Science News 136:106-110 (12 August 1989).

9 Irish elk, from Anthony D. Barnosky, "Paleo- ecology and extinction of Irish elk (Megaloceros giganteus)," lecture at the University of Washington (13 February 1990); see also his "`Big game' extinction caused by climatic change: Irish elk (Megaloceros giganteus) in Ireland," Quaternary Research 25:128-135 (1986).

10 Quotation from Edwin Dobb, "The big picture." The Sciences 29(2):44-50 (1989).

11 Volcano ash potentially rewarming earth by changing albedo: it all depends on how thick it is, whether it warms or insulates. The dark medial stripes of many glaciers, from where lateral debris has collected as two smaller glaciers merge, often causes the underlying ice to melt slower than the surroundings. Glacial "tables" provide another example: If a rock on the glacial surface cannot warm up enough during the day to transmit heat to the underlying ice, then the surrounding ice will melt faster, leaving the rock atop a pedestal. I thank the geologist Neil Fahy for pointing this out to me in the Gulf of Alaska.

11 Stephen E. Zebiak, "Ill Winds: How events in the tropics throw the world's weather out of whack." The Sciences 29(2):26-31 (1989). And for historical data, the news article "La Niña's big chill replaces El Niño," Science 241:1037-1038 (26 August 1988).

18 W. S. Broecker, letter in Science 245:451 (4 August 1989).

Chapter 2. Incrementing Intelligence:
A Principle of Nature?

20 Francis Bacon, The Advancement of Learning (1640).

21 Brain/body ratios, see Harry Jerison, Evolution of the Brain and Intelligence (Academic Press, 1973); for hominid brain/body estimates, see Robert Foley and Robin Dunbar, "Beyond the bones of contention," New Scientist 1686:37-41 (14 October 1989), especially the boxed data from Henry McHenry and Leslie Aiello.

22 Ants are a particularly good example of how "intelligent" behavior seems to be the collective property of a minimum number of contributors. See Thomas D. Seeley and Royce A. Levien, "A colony of mind: the beehive as thinking machine." The Sciences 27(4):38-43 (1987). Nigel R. Franks, "Army ants: a collective intelligence." American Scientist 77:139-145 (March-April, 1989).

Dictionary definitions of intelligence, cleverness, etc., are of little help. Some of the more thoughtful distinctions regarding intelligence are to be found in Horace B. Barlow's "Intelligence, guesswork, language," Nature 304:207-209 (1983), and his entry "Intelligence: The Art of Good Guesswork" in The Oxford Companion to the Mind, edited by Richard L. Gregory, pp. 381-383 (Oxford, 1987). But pigeons are pretty good at guessing new perceptual categories, one of the reasons why I emphasize inventing and judging "novel courses of action" as a basic aspect of human intelligent behavior.

24 W. H. Calvin, The Cerebral Symphony: Seashore Reflections on the Structure of Consciousness (Bantam, 1989), chapter 1. In that book and the present one, I have started the evolution story with the animals of the last 100 million years; for a more complete time scale of evolutionary processes, see my third book, The River that Flows Uphill: A Journey from the Big Bang to the Big Brain (Macmillan 1986, Sierra Club Books softcover edition 1987).

26 For a view that says language is the big step to becoming intelligent, see E. MacPhail, "Vertebrate intelligence: the null hypothesis." Philosophical Transactions of the Royal Society of London B308:37-51 (1985). Tool use isn't necessarily "intelligent": Benjamin B. Beck, "Tools and intelligence." In: Animal Intelligence, edited by R. J. Hoage and Larry Goldman, pp. 135-147 (Washington, D.C., Smithsonian Institution Press, 1986).

27 Oliver Sacks, Seeing Voices: A Journey Into the World of the Deaf (University of California Press, 1989), p. 40. Many prelingually-deaf children raised without Sign will, however, develop their own "home sign" system of much greater sophistication than that of their caregivers: see Susan Goldin-Meadow and H. Feldman, "The development of language-like communication without a language model," Science 197:401-403 (1977). While this indicates that the developing brain can "invent" language without hearing speech, the prospects of such children are still bleak.

30 W. H. Calvin, "The brain as a Darwin Machine." Nature 330:33-34 (5 November 1987). An interesting predecessor from the computer science community to the Darwin Machine concept can be seen in John H. Holland, K. J. Holyoak, R. E. Nisbett, and P. R. Thagard, Induction: Processes of Inference, Learning, and Discovery (MIT Press, 1986). Though neither draws explicitly on the serial-ordered aspect of DNA bases and of antibody amino acids that characterize darwinism in our best-understood systems, Holland's genetic algorithms is the closer analogy to Darwin Machines creating strings of movement commands than is the "neural darwinism" seen in Gerald M. Edelman, The Remembered Present: A Biological Theory of Consciousness (Basic Books, 1989). My review of Edelman's earlier book draws some distinctions: W. H. Calvin, "A global brain theory," Science 240:1802-1803 (24 June 1988).

32 Nicholas Keynes Humphrey's book The Inner Eye (Faber and Faber, 1986) is a good exposition on the role of social life in shaping up intelligence, and Frans de Waal's Peacemaking Among Primates (Harvard University Press, 1989) has many examples of "look-ahead" in a social setting. If you want more, there is Machiavellian Intelligence, edited by Richard Byrne and Andrew Whiten (Oxford University Press, 1988). More conventional analyses of animal mentality can be found in Hoage and Goldman (1986); and Donald R. Griffin, Animal Thinking (Harvard University Press, 1984).

37 Charles Darwin, On the Origin of Species (John Murray, 1859), p. 194.

38 Herbert A. Simon, Models of Thought (Yale University Press, 1979; first appeared in a 1956 paper), p. 20. Closely related to satisficing is good-enough engineering, whose physiological implications are discussed by Lloyd D. Partridge, "The good enough calculi of evolving control systems: Evolution is not engineering," American Journal of Physiology 242:R173-R177 (1982).

39 Copernicus's sun-centered model actually wasn't simpler than Ptolemy's earth-centered one, because Copernicus used circular orbits. It wasn't until Kepler used ellipses that things simplified. See James Trefil, Reading the Mind of God (Scribner's, 1989).

41 Increasing body size is another drive toward behavioral complexity, in the analysis of James Tyler Bonner, The Evolution of Complexity (Princeton University Press, 1988). But body size is surprisingly labile: A. M. Lister, "Rapid dwarfing of red deer on Jersey in the last interglacial," Nature 342:539-542 (30 November 1989). And, 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).

Some of the Hungary-specific material in this chapter first appeared in somewhat different form in my article, "Fast tracks to intelligence (considerations from neurobiology and evolutionary biology)," in Bioastronomy -- The Next Steps, edited by G. Marx (Kluwer, 1988), pp. 237-245.

43 Darwin (1859), p. 191.

46 Flickers, cited in David P. Barash, The Hare and the Tortoise (Viking, 1986), p. 84.

48 Chewing ends of sticks: Y. Sugiyama et al., "Ant-catching wands of wild chimpanzees at Bossou, Guinea." Folia Primatologica 51(1):56-60 (1988).

48 Much has been made of the tendency for behavior to lead the way in evolution ("Free will can guide the evolutionary process" and other such upbeat pronouncements). It was first formulated (in somewhat more obscure terms) in 1894 when three different scientists discovered it: Henry F. Osborn, James Mark Baldwin, and Lloyd Morgan. Today it tends to go under the name "the Baldwin Effect" or the motto "form follows function." It marks the last big discovery of the nineteenth-century followers of Charles Darwin, who clearly laid the foundation for how we now think about thought processes (I describe animal decision-making and human Darwin Machines more fully in The Cerebral Symphony). But their work was largely forgotten when the early mutations-are-everything geneticists turned their backs on Darwin and the psychologists became so enamored of the behaviorist and Freudian extremes that they could tolerate no other way of looking at things. Population thinking, that concern with the changing statistical profile of whole groups which is the key feature of darwinism, does not come naturally to most humans, who more readily identify with an "essence," that "typical type." For the Baldwin Effect, see Robert J. Richards, Darwin and the Emergence of Evolutionary Theories of Mind and Behavior (University of Chicago Press, 1987), p. 452.

51 Darwin (1859), p.182. Loren Eiseley, The Man Who Saw Through Time, (Scribner's, 1973), p. 95.

Chapter 3. Finding a Fast Track to the Big Brain:
How Climate Pumps Up Complexity.

53 Paul Gauguin, as quoted by Humphrey (1986), pp. 172-173.

55 Reconstructing hominid evolution using cues from the great apes: see the various contributions in The Evolution of Human Behavior: Primate Models, edited by Warren G. Kinzey (State University of New York Press, 1987).

56 Kenneth Boulding, quoted in The Environmental Crisis, edited by Harold W. Helfrich (Yale University Press, 1970), p. 160.

56 Russell H. Tuttle, "The pitted pattern of Laetoli feet." Natural History (3):60-65 (1990). R. H. Tuttle, D. M. Webb, and M. Baksh, "The pattern of little feet." American Journal of Physical Anthropology 78(2):316 (1989). "The Laetoli G prints are indistinguishable from those of habitually barefoot Homo sapiens."

58 Sue Taylor Parker and Kathleen Rita Gibson, "A developmental model for the evolution of language and intelligence in early hominids," in Behavioral and Brain Sciences 2:367-408 (1979), identify "extractive foraging of embedded foods" as creating selection for tool use, and so on to intelligence.

58 Chimpanzee sign language references, see Teaching Sign Language to Chimpanzees, edited by R. Allen Gardner, Beatrix T. Gardner, and Thomas E. Van Cantfort (State University of New York Press, Albany, 1989).

59 Hay plays an interesting role midway in civilization, as Freeman Dyson notes in Infinite in All Directions (Harper and Row, 1988). The Roman Empire didn't need to cut grass in the autumn and store it for winter "grazing" because in the Mediterranean basin grass grows well enough in winter for animals to graze; the idea of hay was unknown to the Roman Empire but was known to every village of medieval Europe. Keeping large numbers of horses and cows alive through the winter aided in the development of the northern population centers such as Paris and Berlin, whose economies came to dominate the Mediterranean ones.

62 Ronald M. Nowak and John L. Paradiso, Walker's Mammals of the World, 4th edition (Johns Hopkins University Press, 1983). Black bears have litters of one to four, usually two or three.

67 Mutation rate, see J. S. Jones, "A tale of three cities." Nature 339:176-177 (18 May 1989).

69 Loren Eiseley, The Immense Journey (Doubleday, 1957), p. 51 and p. 54.

72 Herbert A. Simon, Reason in Human Affairs (Stanford University Press, 1983), p. 44.

72 Woodpeckers' empty niche, see Ernst Mayr, Animal Species and Evolution (Harvard University Press, 1963), p. 87.

73 Epidemic originally meant to spread beyond the local deme; endemic means only within a local population, as in "this deme is the only one that exists anywhere," a species unique to the locality.

77 Matt Cartmill, "Misdeeds in anthropology: a review of Bones, Bodies, Behavior, edited by George W. Stocking, Jr." Science 244:858-9 (1989).

78 Erik Erikson, Identity: Youth and Crisis (Norton, 1968).

80 Mayr (1963) p. 371.

81 Most such refuges have been logged off, their ecosystems greatly disrupted, but a few remain. A conflict between different branches of science occurred in the late 1980s, when astronomers wanted to build yet another telescope atop the mountains of southern Arizona in the midst of one of the last Pleistocene refugia, misrepresenting the biologists' ancient ecosystem concerns as a fight over "just one more kind of squirrel." The U.S. Congress, familiar with squirrels but not with ecosystems, overrode the environmental protection laws in 1988 at the request of Arizona politicians concerned that the construction and operations money might go to some other deserving state without a Pleistocene refuge to destroy. A partial account can be found in The Scientist (22 January 1990), pp. 4-5.

The illustration of the last five major ice ages has been adapted from figures 40 and 48 in Imbrie and Imbrie (1986); based on cores from the floor of the Indian Ocean, these records have less regional bias than the Greenland ice cores (which tend to reflect the surface temperature of the North Atlantic Ocean) used for similar illustrations in chapters five and ten.

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

Chapter 4. Neandertal Country:
Some Consequences of a Fickle Climate

87 Heinz Pagels, The Dreams of Reason (Simon and Schuster, 1988), p. 161.

88 John Imbrie and Katherine P. Imbrie, Ice Ages (Harvard University Press, 1986); the Milankovitch quote is from pp. 102-103.

89 R. E. Edwards, J. H. Chen, T.-L. Ku, and G. J. Wasserburg, "Precise timing of the last interglacial period from mass spectroscopic determination of Thorium-230 in corals." Science 236:1547-1553 (19 June 1987).

The illustration of encephalization quotient is taken from the work of Henry McHenry and of Leslie Aiello featured in the New Scientist of 14 October 1989, p. 39.

90 Erik Trinkaus, "The fate of the Neandertals." Lecture at University of Washington (6 February 1990); see his "The Neandertals and modern human origins," Annual Review of Anthropology 15:193-218 (1986).

90 Stature in aboriginal groups, see K. L. Beals, C. L. Smith, and S. M. Dodd, "Brain size, cranial morphology, climate, and time machines." Current Anthropology 25:301-330 (1984).

93 Gracile chimpanzees, see Adrienne L. Zihlman, John E. Cronin, D.L. Cramer, and Vincent M. Sarich, "Pygmy chimpanzee as a possible prototype for common ancestor of humans, chimpanzees and gorillas." Nature 275(5682):744-0746 (1978). Randall L. Susman, "Pygmy chimpanzees and common chimpanzees: models for the behavioral ecology of the earliest hominids," in The Evolution of Human Behavior: Primate Models, edited by Warren G. Kinzey (State University of New York Press, 1987), pp. 72-86.

95 "Juvenile playing-around tendencies" may be useful for discovering a new niche, but aren't as likely to be important for the maintenance of it, if culturally enlightened robusts can equally well exploit it. My guess is that shortened generation time was typically the major factor, with some other aspect of juvenilized brains maintaining the gracile form in the face of harder times.

96 Charles Darwin, as quoted by Ernst Mayr in Scientific American (March 1990), p. 37.

97 The quote is from Stephen Jay Gould's column in Natural History (November 1986), p. 28. The basic reference on brain/body ratio is Jerison (1973).

97 "Features by which humans differ from apes...." For starters, see the list in Richard D. Alexander's Darwinism and Human Affairs, (University of Washington Press, 1979), pp. 209 ff.

98 Alister Hardy's hypothesis can be best read in Elaine Morgan's The Aquatic Ape (Stein and Day, 1982); see her regular updates in New Scientist. For some aspects of aquatic ape proposals and their chronology, see Mile 136-137 of my 1986 book, The River that Flows Uphill. For bonobos (the gracile chimpanzees) as evidencing some aquatic adaptations, see Frans de Waal's Peacemaking Among Primates (Harvard University Press, 1989), pp. 183-186.

98 Savannah theory restatement: C. Owen Lovejoy, "The origin of man." Science 211:341-350 (23 January 1981).

100 "20 percent of land covered..." About 10 million square miles of land are covered at the peak of an ice age (see Imbrie and Imbrie, 1986). My calculation goes as follows: Subtracting 5 million for uninhabited Greenland, Canada, and the northern U.S. leaves 5 million for covering northern Europe and Asia. Europe-Asia-Africa total 32 million square miles, though perhaps a third of Africa and of Central Asia is only marginally habitable. Thus 5 million reduces the inhabitable 25 million by 20 percent; a meltback would expand the remaining core by 25 percent.

102 Latitude effect on stature summarized by Beals et al. (1984).

102 Calories from gathering vs. hunting, see Richard B. Lee, in Man the Hunter, edited by R. B. Lee and I. DeVore. (Aldine, 1968) pp. 30-48.

103 No, I'm not slighting the southern mid-latitudes in temperate zone roles: neither New Zealand nor Chile-Argentina had hominids until 1,200 and 31,000 years ago, respectively, after modern Homo sapiens arrived.

107 "This pump is even simpler than Darwin's": Note, however, that this expand-the-periphery but compress-the-center principle won't work in every case of population fluctuation. The dramatic frontier-type advantage is dependent on the relative rates of frontier movement (the no-land-rush qualification); it may not apply to the end of a drought where the remaining population can quickly space itself out to occupy the newly productive land. And it depends on shaping up a somewhat different frontier genome by special selection pressures (the annual round of selection associated with winter); the margins of a drought-devastated region are unlikely to present opportunities comparable to the herds of megafauna attracted by the good grazing on the glacial margins.

Still, though dramatic accelerations of gradual evolution depend on such qualifications about the rates at which frontiers move and specialize, pumping the periphery of the habitat may be a more general principle relevant to the slower evolution of many species: selection pressures are always the most severe where the species is precariously adapted to its niche, such as at the margins of a habitat. Because climates are always fluctuating to cause substantial alterations in the habitat size and thus population levels (e.g., El Niño causes population crashes among Pacific birds and fish), the frontier-type representation in the total genome may be pumped up repeatedly even in the general case.

This is a simple model, assuming a doughnutlike arrangement: a ring around the outside of the main population with 15 percent of the total area. In real life, it was surely more complicated, if only from the geography having inhabitable areas. As the crows of Europe demonstrate, temperate zone species may be pushed south into refugia that are isolated from one another (eastern and western Mediterranean peninsulas), rather than continuously spread around a single ring. While there is some tendency for temperate zone and central populations to constantly mix, this stirring of the gene pool will be minimized during the expansion phase, the crucial period for this analysis. The invention of boats during the most recent glaciation may have promoted greater mixing of peripheral and central populations.

Fragmentation of the frontier has two consequences, both of which speed up evolution even more. Speciation becomes more likely, as in the crows. And secondly, the contracted population has more of its population living on a margin of the habitat than they would joined into one continuous ring -- and if one lives on the margins of the range, living conditions are marginal. The perimeter-to-population ratio (just a special case of surface-to-volume ratio reasoning) would be even higher, with a higher percentage of the population living in marginal circumstances that speed up natural selection's modifications to the population.

Francis Bacon and Charles Darwin speculated on reasons for the frequent dominance of northern faunas over southern: see Loren Eiseley, Darwin's Century (Doubleday, 1958), pp. 10-11. For flora, however, Europe is something of a special case, with many fewer species of plants than North America or east Asia. As the British botanist Charles Turner explained ("Plant extinctions of the European Quaternary," lecture at University of Washington, 9 January 1990), this is probably because the Mediterranean limits the southern retreat of species during an ice advance, so that species go extinct more readily there rather than surviving in refugia. For a review of how gene flow and regional specialization interact, see N. H. Barton and G. M. Hewitt, "Adaptation, speciation, and hybrid zones," Nature 341:497-503 (12 October 1989).

108 Speciation is, in a sense, more common in the relatively static tropics -- the way that every valley in Hawaii seems to have its own endemic species of fruit fly. But my argument on reproductive quasi-isolation in islandlike refugia seems particularly appropriate to temperate-zone hominid evolution, given that the various isolated groups are always coming back to potentially intermix with each other at each major meltback: whatever reproductive isolation is achieved during geographic isolation will serve to limit backsliding during boom times.

107 Because there is no land for interglacial expansion in Africa, southern Africa might house the most conservative type in spite of its borderline-temperate climate; because of the bottleneck at Suez, Africa might also be invaded more slowly from Eurasia than in a simple model. Southern Africa does have one of the oldest types of mtDNA: Rebecca L. Cann, Mark Stoneking, and Allan C. Wilson, "Mitochondrial DNA and human evolution," Nature 325:31-36 (1 January 1987). "All these mtDNAs stem from one woman who is postulated to have lived about [150,000] years ago, probably in Africa." But just as an English surname may disappear from the church records following generations of all female offspring, so a woman with a rare mtDNA allele may fail to pass it on if only her sons grow up to reproduce. Such loss of alleles in clonal lineages reduces variability; one would expect such loss to be exaggerated in small temperate zone populations, compared to the tropical demes. Such effects could give rise to a substantially different interpretation of where ancestors lived.

The "Eve" interpretation of the mtDNA analyses is quite misleading; to say that all modern peoples have one common ancestor that lived about 150,000 years ago is only to restate the initial assumption of genetic drift. There were many women then living, and their nuclear DNA is to be found in all of us. It's just that the mtDNA inheritance is odd in two ways: the genes aren't regularly shuffled, and they are inherited only from one's mother. Because of this, some variants die out. In a population of n mothers, each of whom produces on average one daughter, it will take about 2n generations for the mtDNA from n-1 of the original mothers to die out via having only sons at some generation along the way. Though the tree-making model itself is most helpful in suggesting when migrations might have occurred, focussing on its singular root is nonsensical; all it tells you is that the genetic drift method is useless for dates older than 150,000 years (just as the carbon-14 dating methods are no good for dates older than about 70,000 years).

108 Punctuated equilibrium: Stephen Jay Gould, in Perspectives on Evolution, edited by R. Milkman (Sinauer, 1982), pp. 83-104.

108 Note that the selection pressures seasonally present at the margins of the habitat could be far more influential than the everyday selection pressures of the average habitat, e.g., infrequently used hunting skills might evolve more rapidly than frequently needed gathering skills in the total population, simply because of ice-age cycling. For hominid evolution, this disassociation promises to create severe difficulties for interpreting fossils: the living conditions when bones were deposited in the African savannah might be unrepresentative of those at the distant margins of the habitat where features were most effectively shaped. Similarly, where less-modified genes can still be found need not mean that this locale was where the ancient genome was shaped up, or where speciation occurred.

109 Dating of the earliest spread of hominids out of Africa is reviewed by Richard G. Klein in his text The Human Career (University of Chicago Press, 1989).

111 Loren Eiseley, The Immense Journey (Doubleday, 1957), p. 55.

Chapter 5. Over the Pole: Surveying the
Ice Ages from a Seat in Heaven . . . . . .

113 Robert Ardrey, introduction to Eugène N. Marais, The Soul of the Ape (1969), p. 21 of the 1973 Penguin edition.

Peter Wadhams, "Evidence for thinning of the Arctic ice cover north of Greenland," Nature 345:795-797 (28 June 1990).

114 A brief introduction to the glaciations is John Gribbin, "The end of the ice ages?" New Scientist 1669:48-52 (17 June 1989). The extensive popular treatment is John Imbrie and Katherine P. Imbrie, Ice Ages (Harvard University Press, 1986), pp. 102-103. D. R. Lindstrom and D. R. MacAyeal, "Scandinavian, Siberian, and Arctic Ocean glaciation: Effect of Holocene atmospheric CO2 variations." Science 245:628-631 (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).

115 Fridtjof Nansen: See my notes in The Cerebral Symphony, pp. 352-353.

117 M. Milankovitch, Canon of Insolation and the Ice Age Problem (Königlich Serbische Akademie, 1941; English translation by the Israel Program for Scientific Translations, 1969). 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.

COHMAP members, "Climatic changes of the last 18,000 years: Observations and model simulations." Science 241:1043-1052 (1988).

118 Iceland's volcanos, see John McPhee's The Control of Nature (Farrar Straus Giroux, 1989).

121 For the fourfold rate differences, see John Imbrie and John Z. Imbrie, "Modeling the climatic response to orbital variations," Science 207:943-953 (1980). There are, however, some significant nonlinearities associated with melting. The coastal glaciers provide an important example of modes of operation. Even when rainfall and temperature are shared by neighboring glacial systems, as at Glacier Bay National Park near Juneau, Alaska, some will be in "retreat mode" and others in "advance mode." If a glacier has retreated far enough back up its valley, the next advance will plow a terminal moraine -- that serves as a coffer dam when reaching the sea, allowing the glacial snout to push far offshore. This makes it difficult for seawater to erode beneath the glacier. When water finally comes in over the top of the coffer dam, one gets a "tidewater glacier." They are an anomaly, cliffs ten stories high above the waterline dropping blocks of ice into the sea. They may have twice as many stories below sea level, with the submerged snout extending far out from the "shoreline". Once sea water does penetrate beneath the submerged section of glacier (and great icebergs begin popping to the surface!), the glacier will rapidly retreat until only a tip is touching the shoreline -- and be unable to advance again to form an ice cliff, at least until retreating far enough to build up another terminal moraine. There may be similar state-dependent situations in the ocean-ice-atmosphere system more generally.

122 W. R. Peltier, "Slow changes in the earth's shape and gravitational field: constraints on the glaciation history and internal viscoelastic stratification." Space Geodesy and Geodynamics (Academic Press, London, 1986), pp. 75-109.

122 When northern glaciers melt back in response to changes in summer sunshine, so do the southern hemisphere glaciers of South American and New Zealand, as Stephen G. Porter points out. That suggests that the northern meltoff is affecting global climate in a big way, overriding the effects of the minimal summer sunshine of the Southern Hemisphere.

49 Greenhouse warming and the chance of triggering another Dryaslike shutdown of the North Atlantic Current: Uwe Mikolajewicz, Benjamin D. Santer, and Ernst Maier-Reimer, "Ocean response to greenhouse warming," Nature 345:589-593 (14 June 1990), do not discuss the Dryaslike episodes, but their simulations of ocean currents do show the decreased North Atlantic deep water production and decreased salinity of surface waters there that Broecker and Denton (1989) identify as precursors of a shutdown.

123 Intermediate meltoffs best correlated with June-July perihelion: from a lecture by the French glacial expert, Robert J. Delmas, "Climatic and environmental information from ice cores." Lecture at University of Washington (14 February 1989).

123 Paul Hoffman's piecing-together of the mosaic geology of Archean North America, Greenland, and Scandinavia is covered in a news story in Discover, (February 1990), pp. 26-27.

126 John Gribbin and Mary Gribbin, "Climate and history: the Westviking's saga." New Scientist 1700:52-55 (20 January 1990). Settlement of Greenland and windows of opportunity from climate change in the North Atlantic. The illustration of medieval-to-modern temperatures of the North Atlantic Ocean is modified from their sidebar.

127 Aurora, see Syun-Ichi Akasofu, "The dynamic aurora." Scientific American 260(5):90-97 (May 1989). Solar output also varies, with implications for climate: Richard R. Radick, G. W. Lockwood, and Sallie L. Baliunas, "Stellar activity and brightness variations: a glimpse at the sun's history." Science 247:39-44 (5 January 1990)

130 Ice-free corridor opening dates: Lionel E. Jackson, Jr., and Alejandra Duk-Rodkin, "Geology of the ice-free corridor," talk at University of Washington (19 January 1988), and John Ives, Alwynne B. Beaudoin, and Martin P. R. Magne, "Evaluating the role of a western corridor in the peopling of the Americas," Circum-Pacific Prehistory Conference, (Lecture in Seattle, 3 August 1989; to be published by Washington State University Press). The illustration of the ice-free corridor and Clovis-Folsom sites was adapted from the more detailed figure of Wendorf (1989).

132 Earliest human habitation dates in the Americas: Roger Lewin's news article "Skepticism fades over pre-Clovis man." Science 244:1140 (9 June 1989).

133 Richard E. Leakey on widespread disappearance of predecessor hominid populations: lecture in Seattle, Washington (25 February 1989).

137 Benjamin Thompson (Count Rumford), quoted by Warren M. Washington in Natural History (March 1990), p. 68.

139 Wallace S. Broecker and George H. Denton, "What drives glacial cycles?" Scientific American 262(1):48-56 (January 1990), pp. 55-56. For a paleosalinity story, see David A. Anati, "Red Sea Salinity." Nature 339:20-21 (4 May 1989).

The illustration of winter ice extent was adapted from Fig. 6 in the review of Broecker et al. (1985).

143 Rebounding bluffs, from a lecture by Stephen C. Porter, director of the Quaternary Research Center, University of Washington (May 1989).

145 Seattle tombstone-cum-park-bench: Robert Fulghum, in It Was On Fire When I Lay Down On It (Villard, 1989), pp. 209-210, may have remembered the quotation incorrectly -- but not the sentiments! The tombstone is not entirely anonymous: the surname Whitebrook can be inferred from the family plot.

146 Puget lobe of Cordilleran glacier, see Robert Burns, The Shape and Form of Puget Sound (University of Washington Press, 1985); Thomas A. Terich, Living with the Shore of Puget Sound and the Georgia Strait (Duke University Press, 1987). Ocean circulation theory, see Broecker and Denton; their figure on p. 52 shows the advance and retreat of Washington State glaciers.

Chapter 6. Mount Rainier:
Growing Up in a Boom Time

149 Charles Darwin, On the Origin of Species (John Murray, 1859), pp. 481-482.

155 James Hanken, "Development of evolution in amphibians." American Scientist 77:336-343 (July 1989). R. D. Semlitsch and H. M. Wilbur, "Artificial selection for paedomorphosis in the salamander Ambystoma talpoideum." Evolution 43(1):105-112 (1989).

156 Stephen Jay Gould, Ontogeny and Phylogeny (Harvard University Press, 1977), pp. 177 ff.

157 Walter Garstang, Larval Forms With Other Zoological Verses (Basil Blackwell, 1951), p. 62.

157 Adult development finally implementing typically truncated features, see Aldous Huxley's cautionary novel After Many a Summer Dies the Swan (Harper, 1939).

158 Juvenile advantages in adulthood: I discuss this in The Throwing Madonna: Essays on the Brain (Bantam, 1991), chapter 3.

158 The first species to fill a "new niche" may, of course, not be able to hold it, e.g., the grasslands-to-forest succession.

159 Clifford J. Jolly and Jane E. Phillips-Conroy, "Bulls, bears and baboons: the evolutionary significance of developmental plasticity." American Journal of Physical Anthropology 75(2):227 (1988). Robert M. Sapolsky, "Lessons of the Serengeti." The Sciences (May/June 1988). See also his "Junk food monkeys," Discover 10(9):48-51 (September 1989). Jeanne Altmann has shown that garbage-fed baboons mature faster and have more babies, and Sapolsky has found that they have cholestrol levels one-third higher than savanna baboons (see Natural History, May 1990, p. 107 for a picture).

160 Animals that adjust their reproductive policy, see Paul Colinvaux, Why Big Fierce Animals Are Rare (Princeton University Press, 1978), p. 16.

165 Supernormal releasers and attractors, see David P. Barash, The Hare and the Tortoise (Viking, 1986), pp. 84-86, and Annie Dillard, The Writing Life (Harper and Row, 1989), p. 18. These behavioral attractors are quite different from the "strange attractors" of chaotic systems, more like the attractions of quicksand than the "gravitational centers" of chaos.

30 David Brin, "Neoteny and two-way human sexual selection" (unpublished manuscript, 1990). Brin's suggestion that juvenilized appearance in females might preferentially attract nurturing males has several interesting consequences, as he points out: it helps to explain the unusual (compared to other mammals) amount of attention-attracting female adornment (which currently supports an enormous cosmetics and fashion industry), and it helps to explain pedophilia. If male preference for juvenile-appearing females coevolved with paedomorphosis, then one might expect more than the usual (for other primates) amount of misplaced sexual attraction toward juveniles. Brin suggests that the unusual-for-mammals breasts of the human female (which are 85 percent fat pad) might serve as a sexual releaser, helping the sexually-interested male to distinguish between appropriate and inappropriate juvenile-appearing females.

168 Adolescent growth spurt, see J. M. Tanner, Foetus into Man: Physical Growth from Conception to Maturity. (Harvard University Press, 1978), p. 14. Growth in general (and models for the adolescent growth spurt associated with sexual maturity, in particular): Barry Bogin, Patterns of Human Growth (Cambridge University Press, 1988). For juvenile periods of various species, see P. H. Harvey and T. H. Clutton-Brock, "Life history variation in primates." Evolution 39:559-581 (1985).

Juvenilization, neoteny, and paedomorphism are not really synonymous. See Bogin (1988, p. 71), Gould (1977, p. 179), Ashley Montagu, Growing Young (McGraw-Hill, 1981), and F. Harvey Pough, John B. Heiser, and William N. McFarland, Vertebrate Life, 3rd edition (Macmillan, 1989, p. 68).

My own summary of the confusing terminology: what is here called paedomorphosis ("child-shaped") or juvenilization is simply descriptive of the appearance of the end-product, without implication of mechanism. Lately neoteny has been used by some, but not all, authors to refer to the slowing ("retardation") of somatic development. Progenesis, on the other hand, refers to paedomorphosis associated with accelerated somatic development plus the truncation of ontogeny. Thus, compared to the apes, we are both neotenized (somatic development retarded to half the pongid rate) and paedomorphic. But compared to modern-type Homo sapiens earlier in the last ice age, we exhibit progenesis in the same sense as, compared to wild-types, the domestic animals exhibit progenesis.

168 For the invertebrate-to-chordate transition, see Q. Bone, The Origin of Chordates (Oxford University Press; Carolina Biology Readers #18, 1979), or p. 70 of Pough (1989).

171 C. Loring Brace, Karen R. Rosenberg, and Kevin D. Hunt, "Gradual change in human tooth size in the late Pleistocene and post Pleistocene." Evolution 41:705-720 (1987). And C. Loring Brace, The Stages of Human Evolution, 3d edition (Prentice-Hall, 1988) -- though, as Kathleen Gibson notes (personal communication, Cascais, Portugal, 22 March 1990), simple truncation of tooth growth by precocious puberty will not explain tooth size reduction, as tooth size is seemingly determined much earlier in childhood. James M. Calcagno, Mechanisms of Human Dental Reduction (University of Kansas Publications in Anthropology No. 18, 1989). One of the hazards of the simplified treatment of early puberty which I and others utilize is that it leads us to think of early puberty occurring as if the living conditions suddenly improved at the time of truncation -- when, of course, they are usually spread out over the previous decade and influence somatic growth as well as menarche.

173 Rose E. Frisch, "Fatness and fertility." Scientific American 258(3):88-95 (March 1988). See also Science 185:949-951 (13 September 1974), and 199:22-30 (6 January 1978).

174 Deer on the Kaibab Plateau of Arizona, see John P. Russo, "The Kaibab North Deer Herd," a 1964 publication of the Arizona Department of Fish and Game.

174 Humans perhaps too K-selected, see Lovejoy (1981).

177 Jerome Kagan, J. Steven Reznick, and Nancy Snidman, "Biological Bases of Childhood Shyness." Science 240:167-171 (8 April 1988).

178 Victor H. Dennenberg, "Hemispheric laterality in animals and the effects of early experience." Behavioral and Brain Sciences 4(1):1-50 (March 1981).

179 Richard D. Alexander, The Biology of Moral Systems (Aldine de Gruyter, 1987), p. 23.

180 The "28-year-old grandparent" phenomenon has been commented upon by people who work in hospital maternity wards, e.g., Melvin Konner, Becoming a Doctor: A Journey of Initiation in Medical School (Viking, 1987).

181 Susan Oyama, The Ontogeny of Information: Developmental Systems and Evolution (Cambridge University Press, 1985), p. 188.

Chapter 7. Whidbey Island:
Ratcheting Up Brain Size

183 Leonard A. Sagan, "Family ties." The Sciences 28(2):20-29 (March 1988).

189 Ruth Kirk with Richard Daugherty, Exploring Washington Archaeology. (University of Washington Press, 1978). Note that ice age fishing villages would have been covered up by rising sea level, unless the land uplifted at a faster pace. There are some sites along the Alaskan panhandle coastline where uplift could have preserved an early Holocene fishing village: Bruce F. Molnia, "Glacial history of the northeastern Gulf of Alaska: A synthesis." In Glaciation in Alaska: The Geologic Record, edited by T. D. Hamilton, K. M. Reed, and R. M. Thorson (Alaska Geological Society, 1986), pp. 219-236.

190 Death in childbirth, see Sue Armstrong, "Labour of death," New Scientist 1710:50-55 (31 March 1990). "All but 1 per cent of these maternal deaths take place in the Third World, where the average lifetime risk of dying as a result of pregnancy is between one in 25 and one in 50; this compares to a lifetime risk of between one in 4000 and one in 10,000 for a woman in the developed world."

191 Hat size and IQ, see Stephen Jay Gould, The Mismeasure of Man. (Norton, 1981).

191 Kin selection by big heads, see W. H. Calvin, "The great encephalization: throwing, juvenilization, developmental slowing, and maternal mortality roles in prehuman brain enlargement." Human Ethology Newsletter 5(3):4-6 (September 1987). And also W. H. Calvin, "Of fast teeth and big heads." Nature 328:481 (6 August 1987).

193 Despite our perceptual abilities to guess a racial designation from a collection of traits such as skin color, hair color and stiffness, eye color, and facial shape, the serious study of the subject suggests that we are simply inventing pigeonholes ("categorical perception") along a continuous distribution of traits. There is, however, a tendency called assortitive mating where people tend to pick mates for themselves or their children on the basis of physical similarity; this tends to maintain distinctive groupings of physical traits that might arise by chance. Such considerations of "beauty" may be simple sexual selection with no rhyme or reason -- but sexual selection often has some natural selection rationale, however exaggerated and inappropriate the extremes to which it is taken (those long or iridescent bird tails probably started out as simple female preference for mates healthy enough to grow new feathers; women in many parts of the world prefer tall men as mates, stature being an indirect indicator of successful childhood development).

And the birth canal bottleneck could be the rationale for some such human mate selection, given how obstetricians worry about difficult deliveries when the wife is petite and the husband isn't. Any random (but heritable) tendency to select a body type similar to one's parents or siblings would be reinforced by improved survival of offspring and mothers. And so the birth canal bottleneck might have helped maintain local standards of "beauty" (and, alas, reinforced racism).

194 Heritability of early menarche: Tanner (1978), p. 126.

195 Herbert A. Simon, Reason in Human Affairs (Stanford University Press, 1983), p. 50.

195 F. Brown, J. Harris, R. Leakey, and A. Walker, "Early Homo erectus skeleton from west Lake Turkana, Kenya." Nature 316:788-792 (1985).

195 Secular trend in height, see Tanner (1978), p. 150.

196 Peter K. Stevens, Patterns in Nature (Little, Brown 1974), p. 25.

199 Theodosius Dobzhansky, "Discussion." In Insect Polymorphism, edited by J. S. Kennedy (Symposia of the Royal Entomological Society, 1961), p. 49.

201 James Lovelock in The Ages of Gaia (Norton, 1989) gives a nice treatment of those population boom-and-bust equations for general readers.

201 Oscillations in population size, see Paul Colinvaux, Introduction to Ecology (Wiley, 1973), pp. 483-485.

201 How might domestication thoroughly embed a juvenilized form of the species if natural selection operated upon the r-shift itself? This is somewhat like asking why those invariably-aquatic axolotls might have evolved from those conditionally aquatic Ambystoma -- again it is a question of how the conditional feature might have been lost without natural selection for losing it.

It's potentially like that recessive gene which, when two are present, causes sickle-cell anemia -- but when only heterozygous, protects against malaria (and so is selected for, in low-lying tropical areas with the mosquitos that spread malaria). Only in my theory, the homozygous condition causes sure-fire acceleration rather than the conditional-on-climate acceleration of the heterozygous case.

Ordinarily you'd think that the natural selection would operate on the flexibility, so that the body features would spring back to the old average once the climate stabilized at a new mean. But there are some ways in which accelerated maturity might become unconditionally established despite an origin in a series of conditional r-shift events. Suppose we have one version (allele) of a developmental rate gene that, when homozygous (the individual has two copies and so no other choices), leads to accelerated maturity. When neither allele at this position in the chromosome is the special allele, one gets average developmental rates. But if one version is present, and the other is the standard allele, one gets a precarious balance between acceleration and standard. And so the special accelerated version is conditionally used: the occasions being when the environment improves (the better nutrition, increased daylight, higher population density, or whatever). Since the phenotypes will be more successful under such conditions, the allele will become more and more common in the general population. Some individuals will become homozygous for it, and thus always accelerated in maturity, unconditionally juvenile in adult appearance.

202 The enormous plasticity of adult body size can be seen in the poorly-understood reduction in body size of mammals in isolated demes; pygmy races of elephants and rhinoceros have been found on islands. But it wasn't until someone studied fossils of the European red deer on Jersey that we realized how fast body size could change, absent artificial breeding: 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). Was this due to resource limitations? Lack of predators? No one is sure; were there a boom-time due to omission of predators or pathogens from the new island, juvenilized variants that reach reproductive age sooner might come to eventually dominate the gene pool (because they have more offspring per century than those with standard menarche). Note that lack of certain pathogens (one of the virtues of isolation) might allow small adults to more successfully raise offspring; lack of predators per se is not required. After the glaciers again lowered sea level to reconnect Jersey to the mainland, the dwarf deer disappear from the fossil record.

204 Eiseley (1957), p. 125, pp. 129-131.

Chapter 8. Hand-ax Heaven:
The Ambitious Ape's Guide to a Bigger Brain

206 Ernst Mayr, Toward a New Philosophy of Biology (Harvard University Press, 1988), p. 95.

207 Mastodon: Kirk and Daugherty (1978), p. 28.

208 Ernst Mayr, "Descent of man and sexual selection." In L'Origine dell' Uomo (Academia Nazionale dei Lincei, 1973), pp. 33-61.

209 Tool-use by animals, see pp. 575-578 of The Oxford Companion to Animal Behaviour, edited by David McFarland (Oxford University Press, 1987).

209 Christophe Boesch and Hedwige Boesch, "Sex differences in the use of natural hammers by wild chimpanzees: a preliminary report." Journal of Human Evolution 10:585-593 (1981), and film shown at Tools, Language, and Intelligence: Evolutionary Perspectives workshop in Cascais, Portugal (19 March 1990).

209 Cooperative hunting: Shirley C. Strum, "Baboon cues for eating meat." Journal of Human Evolution 12:327-336 (1983). Geza Teleki, "The omnivorous chimp." Scientific American 228(1):32-42 (1973). Frans X. Plooij, "Tool-use during chimpanzee's bushpig hunt." Carnivore 1:103-106 (1978). C. Boesch and H. Boesch, "Hunting behavior of wild chimpanzees in the Taï National Park." American Journal of Physical Anthropology 78:547-573 (1989).

210 Throwing by chimpanzees, see Plooij (1978); Jane Goodall, In the Shadow of Man (Houghton Mifflin, 1971) and The Chimpanzees of Gombe (Harvard University Press, 1986), p. 550; and Frans de Waal, Chimpanzee Politics: Power and Sex Among Apes (Harper and Row, 1982).

211 Chimpanzees throw in a variety of humanlike styles, see Jane Goodall, "The behaviour of free-living chimpanzees in the Gombe Stream Preserve." Animal Behaviour Monographs 1(3):161-311 (1968) at p. 203. But, as Sue Savage-Rumbaugh pointed out to me, many of those postures are associated with male threat displays and are unlikely to be associated with "get set" styles that might lead to precision throwing.

The illustration of Acheulian "hand axes" is adapted from drawings by C. O. Waterhouse at the British Museum (Natural History). The smaller one is a "twisted ovate" from St. Acheul, France. The larger is the one associated with the Swanscombe skull in England. While the Acheulian tool kit went out with Homo erectus, bifaces shaped like Acheulian hand axes are also seen in Homo sapiens tool kits, e.g., the one from Le Moustier at Musée de l'Homme in Paris).

214 H. G. Wells, Tales of Space and Time (Doubleday and McClure, 1899); for a general introduction to hand axes and the associated toolmaking styles, see John Gowlett, Ascent to Civilization (Knopf, 1984), pp. 60 ff. 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). Spin for throwing into flocks of birds: M. D. W. Jeffreys, "The hand bolt." Man 65:154-154 (1965).

214 Hand axes in dried-up ponds, etc.: Glynn Ll. Isaac, Olorgesailie. (University of Chicago Press, 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).

215 William D. Hamilton III, "Geometry for the selfish herd." Journal of Theoretical Biology 31:295-311 (1971).

216 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). And my subsequent book The River that Flows Uphill: A Journey from the Big Bang to the Big Brain (1986).

219 The big cats sometimes leap onto the back of a much larger herd animal and bring it down; the cat's claws might active the same withdrawal reflex that lowers the hindquarters.

219 Patrick D. Wall, "On the relation of injury to pain." Pain 6:253-264 (1979).

221 "Killer Frisbee": Albert Leo of Pomona College suggested this name (June, 1988), which is sure to be disavowed by anthropologists.

222 "Manuports," see Mary D. Leakey, Olduvai Gorge. Vol. 3. (Cambridge University Press, 1971).

222 Barbara Isaac, "Stone throwing and human evolution." Unpublished MS; see news article in Discover 7(6):6-7 (June 1986).

226 Pruning of connections in cerebral cortex is reviewed in The Cerebral Symphony, p. 165, 362. The loss of neurons is from J. B. Lohr and D. V. Jeste, "Studies of neuron loss with age in three different brain regions in humans," Society for Neuroscience Abstracts 15:22 (1989). For monkey motor cortex, see J. Tigges, J. Herndon, and Alan Peters, "Neuronal changes in Area 4 during the life span of the rhesus monkey," Society for Neuroscience Abstracts 15:259 (1989); they report that this movement control area of the leg loses nearly a third of its neurons between infancy and early adulthood [my wife suggests that the monkeys must have killed off their clumsy neurons!].

The illustration of synaptic density in visual cortex uses the human data of P. R. Huttenlocher, "Synapse elimination and plasticity in developing human cerebral cortex." American Journal of Mental Deficiency 88:488-496 (1984). The monkey data is from 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). I have replotted the data to normalize peaks and used a logarithmic time scale starting at about 120 days after conception and ending about ten years after birth. In addition to breaking synapses and withdrawing axon collaterals, there is also some cell death in cerebral cortex during the same period. The lateral shift in the human curve relative to the monkey curve would be consistent with a two- to three-fold slowing of human somatic development.

227 Paul Cheney and Eberhard E. Fetz, "Comparable patterns of muscle facilitation evoked by individual corticomotoneuronal (CM) cells and by single intracortical microstimuli in primates: evidence for functional groups of CM cells." Journal of Neurophysiology 53:786-804.

229 Not all hunters are male: see A. Estioko-Griffin, "Daughters of the forest." Natural History 95(5):36-43 (1986).

232 Eiseley (1957), p. 140

Chapter 9. San Juan Ferry:
Does Consciousness Emerge from Cortical Consensus?

240 Dean Falk, "Brain evolution in Homo: The `radiator' theory." Behavioral and Brain Sciences (in press, 1990).

242 Jeffrey T. Laitman, "The anatomy of human speech." Natural History 93(8):20-27, 1984. And Phillip Lieberman, The Biology and Evolution of Language (Harvard University Press, 1984)

251 From an entirely different perspective, involving cortical injuries and developmental abnormalities, the neuropsychologist Marcel Kinsbourne also arrives at the suggestion that conscious attention corresponds to the widespread activation of many regions of cerebral cortex (the quote is from "Integrated field theory of consciousness," in Consciousness in Contemporary Science, edited by A. J. Marcel and E. Bisiach (Clarendon Press, Oxford, 1988), pp. 239-256. The philosopher Daniel C. Dennett emphasizes that conscious perception takes time, much more than any of the component processes; again, this can be predicted from Darwin Machine reasoning applied to both sensory and movement schema sequences, as it takes many Darwin Machine generations to achieve a widespread consensus (Bellagio workshop on consciousness, 26-31 March 1990). Hierarchies, such as the acoustics-phonemes-syntax-semantics levels of analysis which seem to help us understand sentences, may be helped by Darwin Machine architectures that can be parasitized for language uses and staged appropriately.

The bar-code analogy also helps one understand why various attempts to measure this consensus might succeed or fail. Were the representation a string in time (as when the optical wand is swiped across the bars), and the strings in various areas synchronized in time, we might see the EEG from various regions move up and down in synchrony (the EEG coherence is a measure of this). But if the strings were out of phase with one another (if I were designing such a system, I'd do that to prevent out-of-control oscillations such as seizures), it might be much harder to detect string consensus in various regions. And if the representation were instead spatial (like the bar code on the package), merely repeating in the manner of wallpaper designs, we might require a very sensitive imaging method to detect the consensus.

256 Oswald Spengler, The Decline of the West (Knopf, 1926), vol. 1, p. 166 of the abridged edition.

Chapter 10. Friday Harbor:
Is There Intelligent Life on Earth Yet?

258 Alison Jolly, "The evolution of purpose." In Machiavellian Intelligence, edited by Richard W. Byrne and Andrew Whiten (Clarendon Press, 1988), pp. 363-378 at p. 378.

259 Chief Seattle, 1854, quoted from a U.S. National Park Service exhibit in Seward, Alaska.

260 Alfred W. Crosby, Ecological Imperialism: The Biological Expansion of Europe, 900-1900 (Cambridge University Press, 1986). Role of disease, firearms in conquering virgin continents.

269 Edwin Dobb, "The big picture." The Sciences 29(2):44-50 (1989), at p. 49.

270 Gaia, alas, is only capable (at most) of keeping things suitable for plants and simple animal life -- not intelligent life. See James Lovelock, The Ages of Gaia (Norton, 1988).

272 Paul R. Ehrlich and Anne H. Ehrlich, The Population Explosion (Simon and Schuster, 1990). "The critical prerequisites to reduced fertility are five: adequate nutrition, proper sanitation, basic health care, education of women, and equal rights for women. The first four factors reduce infant mortality, allowing a reasonable expectation that a given child will survive to adulthood. Female education is an especially interesting and in some ways the most unexpected finding. Women will apply even a few years of schooling to improving life for their families by providing more nutritious, balanced meals and better home health care and sanitation... Improving the home situation reduces infant and child mortality, making men and women more receptive to the idea of smaller families. And the women's education makes them more open to contraception and better able to employ it properly. Finally, when women have sources of status other than children, family size often decreases."

272 Alas, those breakwaters exist no more, thanks to an ill-conceived plan to double the width of the Northwestern University campus by filling in the lake. Inelegant riprap, a jumble of broken concrete slabs representing the throw-away building era, has replaced the sand beaches. Northwestern has created a lagoon in the midst of its landfill, though with the unmistakably uniform contours created only by bulldozers. But the outer strip of walkway between lagoon and lake has some of the sense of the old breakwaters.

274 Jared Diamond, "The worst mistake in the history of the human race", in Discover (May 1987), p. 64 ff. See also Mark N. Cohen and George J. Armalagos, editors, Paleo- pathology at the Origins of Agriculture, (Academic Press, 1984).

275 History of technological civilizations from a lecture by Professor Jon Bridgman, University of Washington (25 May 1989).

277 Paleo-Indians as searching for the source of the aurora: This variant on "looking for the pot of gold at the end of the rainbow" occurred to me when I noticed that the magnetic pole was east and north of the Mackenzie River delta, east of those North Slope oil fields and wildlife refuges. Indians in Siberia following the aurora would have been led to the Bering Strait; once within Alaska, they would have been led up north around the mountains that, during the ice age, blocked other routes east and south. And so they could have discovered the Ice-free Corridor to Montana, just by initially trying to find the most intense "root" of the Northern Lights.

278 "Infiltration of mind into the universe...." Freeman Dyson, Infinite in All Directions (Harper and Row, 1988), p. 118.

278 "Gould's Principle...," see Stephen Jay Gould, The Flamingo's Smile (Norton, 1985), p. 401.

279 Norman Mailer, in accepting the 1969 National Book Award for The Armies of the Night.

280 Stephen H. Schneider, "The greenhouse effect: science and policy." Science 243:771-781 (10 February 1989). And his book Global Warming: Are We Entering the Greenhouse Century? (Sierra Club Books, 1989). See the "Managing Planet Earth" issue of Scientific American (September 1989).

The illustration of the cold spikes in the North Atlantic Ocean since the last interglaciation is adapted from the Camp Century core (east of Thule, northern Greenland) shown in Figure 4 of Dansgaard et al. (1982). It is based on the oxygen isotope ratio; seen in ocean floors, the slow trends in this ratio tend to reflect ice volume (filtered by mixing times) but the rapid changes from ice cores may be due to the surface temperature of the North Atlantic Ocean at the time of evaporation in the mid-latitudes (higher temperatures aid in the "launch" of the heavier water molecules containing the oxygen-18 isotope); this water subsequently fell on northern Greenland as snow and was compacted into ice layers. Rapid fluctuations may also be influenced (e.g., Fairbanks 1989) by surges of fresh water into the Atlantic from ice dams breaking and draining huge lakes of meltwater via the St. Lawrence River.

281 W. S. Broecker, letter in Science 245:451 (4 August 1989).

49 Simulations of North Atlantic Current's deep water production: Uwe Mikolajewicz, Benjamin D. Santer, and Ernst Maier-Reimer, "Ocean response to greenhouse warming." Nature 345:589-593 (14 June 1990). This is only the first round of such simulations of ocean-atmospheric linkage; successor models will hopefully simulate the Current in more detail and analyze its stability.

286 John Maynard Smith, Did Darwin Get It Right? Essays on Games, Sex, and Evolution (Chapman and Hall, 1988), p. 37.

289 Most governments are still treating scientific research in the ocean-atmosphere systems as if it were just another aspect of routine agricultural research. Or of improving weather forecasting. Hardly as serious a matter as, say, the perceived need for yet-another new "defense" system, or bailing out the Chrysler Corporation, or rescuing the savings-and-loan-association gamblers. Those examples from recent U.S. history involve industries that, unlike science, contribute mightily to politicians' campaign funds as a way of gaining a hearing for their industry's problems. They may not be able to buy solutions, but they can keep their problems from getting placed on a back burner via contributions and high-priced lobbyists. And their problems are, relatively speaking, easily comprehended. Getting the politicians' attention is sometimes hard for scientific-based agendas, given that the politicians are mostly lawyers who avoided science courses in college, who think mostly in terms of creating prohibitions rather than plans, using penalties rather than preparedness.

The illustration showing the end of the last glaciation, as seen from northern Greenland (Camp Century) and from Antarctica (Byrd Station) ice cores. Adapted from Fig. 2 of the Broecker et al. (1985) review; data from S. Johnsen, W. Dansgaard, H. Clausen, and C. Langway, Nature 235:429-434 (1972).

The illustration of the Allerød-Dryas chattering, and the speed of the end of the Younger Dryas, was adapted from Fig. 1 of Dansgaard et al. (1989) and utilizes the ice core at "Dye 3" in southern Greenland.

290 "Like an Old Testament god with lots of rules and no mercy" is, I confess, what Joseph Campbell said in his interview with Bill Moyers on Nova (1988) -- but about personal computers, not climate!

290 Another redirected characterization: I have adapted the Conrad bad-weather-ahead tale from that (this time regarding nuclear terrorism) by Luther J. Carter, Nuclear Imperatives and the Public Trust, excerpted in Issues in Science and Technology (Winter 1987), p. 60.

291 A. E. Housman, lines 9-16 of "Smooth between sea and land." In More Poems (Knopf, 1936), p. 64.

The Author

William H. Calvin, Ph.D., is a neurophysiologist on the faculty of the University of Washington in Seattle. During the 1960s and 1970s, his research interests were largely concerned with how individual nerve cells function electrically. During the 1980s, he became interested in the problems that overlap neurobiology, anthropology, evolutionary biology, and developmental biology -- especially the fourfold increase in the brain size of hominids during the past 2.5 million years and the attainment of language and plan-ahead consciousness.

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