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

copyright ©2002 by William H. Calvin
ISBN 0-226-09201-1 (cloth)    GN21.xxx0     
Available from or University of Chicago Press.
Webbed Reprint Collection
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

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To:                  Human Evolution E-Seminar
From:             William H. Calvin
0.61215°N    36.02245°E    985m ASL
                        Lake Baringo
The earliest hominids

I’m looking northwest from the shores of Lake Baringo toward the Tugen Hills.  They have long been thought to be a good place to look for missing links, as their layers go from about 250,000 years old down to about 14 million years old.  In a deep ravine near Kapsomin, about 50 km from here, a French-Kenyan paleoanthro team is excavating the five earliest-known hominid individuals.  The nearby volcanic layers seem to date them back to the Late Miocene, about 6 million years ago.

     It will be years yet before the paleoanthropology community agrees on how to place them, together with the new finds in the Middle Awash region of Ethiopia at 5.8 million; both early hominids appear to have lived in relatively wet woodlands.  Those dates are right about when the DNA dating suggests we last shared a common ancestor with the chimp-bonobo branch.  “Millennium Man” is upright but it still shows signs (paleoanthropologists love to talk about curved bones) of apelike specializations for life in the trees.

     Ron Clarke’s new Sterkfontein “Stw573” skeleton at 3.3 million years ago still has feet that can grab a tree branch, along with its weight-bearing heel bone.  So real efficiency in bipedal stride may have taken over three million years to develop after upright stance did – maybe even as long as it took brains to finally start enlarging at 2.4 million years ago.

     Doing paleoanthropology is much like doing a jigsaw puzzle without a picture of the pattern – and where you have to dig to discover the pieces!  And then the pieces are worn and broken, making them ambiguous, able to fit into several different places in your imagined pattern.  You guess at the pattern, using information from elsewhere in evolutionary biology and paleontology as a guide, but the general guiding principles such as Darwinism and analogies from development are very broad, leaving lots of room for sheer happenstance.

     Human evolution from an apelike ancestor only happened once, and the general principles merely tell you something about what the average result might be if you ran the experiment a hundred times.  And so paleoanthropologists have to guess a lot.  This makes for lively controversies.  Reading a historical account of paleoanthro (try Ian Tattersall’s The Fossil Trail or Alan Walker and Pat Shipman’s The Wisdom of the Bones) shows you how the current ideas have been built up.  The track record shows you how likely it is that the current ideas are also missing a few important things.

     Walking back from dinner in the dark, fully bipedal, we ran into the hotel’s uniformed askari.  My cousin asked him in Swahili if hippos really came up on the lawn outside our front doors.  Oh yes, the guard said, pulling out his flashlight, and he led us down the path past our cabins – and there in the dim light were two full-sized hippos, mowing the grass.

     They come up all through the night in different groups, sometimes a half-dozen at a time.  So you sleep fitfully under your mosquito netting, listening for exaggerated treble and bass sounds, for malarial buzzing inside the room and for two-ton munching sounds just outside.  At least no troop of baboons bounced on my roof for half the night.


We took a nice hour-long boat ride in the early morning light and saw hippos chasing one another, crocs beginning to sun themselves on shore, herons hopefully inspecting the shallows, some cormorants diving farther offshore.  Besides all the colorful small birds (weavers are very common here), there were hornbills, Marabou storks, and fish eagles.

     People were coming down to the lake edge to haul water, wash clothes, and fish.  We saw the little one-person boat of lashed-together firewood called a coracle, about the size of a floating lawn chair.  Like the tidal fish trap, it doesn’t hold water, but the sticks keep the fisherman afloat.  His catch is kept in the bottom of the boat and benefits from the constant change of water.  The fisherman paddles with split shells, one in each hand.  Close inshore (where it’s shallow enough to wade ashore), and at the flat water of dawn, this technique is just fine.  It provides an interesting view of how boats might have gotten started and become valued.

     Then after breakfast, we looked up to see a camel working over the local trees.  Perhaps, I said speculatively, some camels have been driven south from Lake Turkana by the current dry spell.  Around here it has been raining on and off for the last week, so we are seeing desert-bloom conditions.  We almost stumbled over a medium-large tortoise crossing the grass to browse on the well-watered bushes.  The hotels don’t have to bait the premises to get animals to come visit the tourists.  All they have to do is to water the plants and wait.

So the cousin, who is busy finishing up a book manuscript, and I were sitting in the shade, keeping an eye on the camel and the hippos from our lawn chairs, each nursing the battery life in a laptop computer while trying to get some work done.  We kept hearing this faint bugle-like noise.  It sounded somewhat like one of those miscellaneous computer vocalizations.  But it stopped after several repetitions.

     I’d already been fooled by a bird that sounded like a truck back-up warning horn, and another that sounded like a telephone.  I was perfectly willing to believe in a bird-call that duplicated a computer sound, just like those starlings in Copenhagen that imitate cell-phone rings and perplex the pedestrians.  A half-hour later, we heard that bugle sound again.  And again.  We kept commenting on it, speculating about bird mimicry, and going back to work.

     Then a window popped open on my computer screen.  It contained the name of the cousin’s computer, not mine.  Realization dawned.  The infra-red ports on the two laptops had discovered each other, had exchanged names, and had been repeatedly announcing the fact.  I’m sure no one else at Baringo (and certainly not the camel) understood why we laughed uproariously for minutes, at the absurdity of it all happening in this particular setting.

There is something fascinating about science.  One gets such wholesale returns of conjecture out of such a trifling investment of fact. 
- Mark Twain, Life on the

     After lunch, we saw a fish eagle and two crested cranes near the dock.  That’s when the camel came over to us, looking for a handout.  If a camel could ever be said to have an ingratiating smile – well, no, I suppose this one just looked opportunistic.  So it is likely an experienced local camel, well versed in the ways of tourists, not a recent refugee from the wilds of Turkana.

     Some speculations can be disproved faster than others, which may take a lifetime to show their flaws.  This is what makes paleoanthropology so frustrating.



Notes and References
(this chapter
corresponds to 
pages 150 to 154 of the printed book)

Copyright ©2002 by
William H. Calvin

The nonvirtual book is
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All of my books are on the web.
You can also click on a cover for the link to

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)

The six out-of-print books are again available via Authors Guild reprint editions,
also available through (click on cover):

Inside the Brain

The Throwing Madonna:  Essays on the Brain

The River That Flows Uphill


The Cerebral Symphony

The Ascent of Mind

How the Shaman Stole the Moon