Email Calvin || Glossary || Book's Table of Contents || Calvin Home Page  


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

Return to previous chapter


To:                  Human Evolution E-Seminar
From:             William H. Calvin
48.9°N     2.3°E 
            Musée de l’Homme in Paris                       

Subject:            The Ghost of Habitats Past 


After the meetings on the emergence of language broke up, an anthropologist friend and I headed over to Musée de l’Homme to see their excellent new Homo erectus exhibit, an inspired improvement on what used to be an endless display of stones and bones – the “hard evidence,” if you like.

          The general up-from-the-apes outline, for those who don’t know it already, starts with apes evolving from the Old World Monkeys more than 25 million years ago.  Gibbons split off about 18 million years ago.  Great apes, at least since the common ancestor with the orangutans 12-16 million years ago, have had twice the brain of a similarly-sized monkey.  The vegetarian gorilla, with the enormous gut and jaws to match, split off about 7-8 million years ago.

          Chimpanzees are more omnivorous, with lots of ways of making a living.  Our last common ancestor with the chimps and bonobos was 5-6 million years ago, and that tends to be the point of departure for hominid discussions.  We start with something like a great ape, omnivorous but with a gut still accustomed to mostly fruit and leaves, not to major amounts of meat and fat.  This apelike ancestor was capable of short bouts of walking upright, but not really adapted to sustained upright posture and efficient running.  It likely had a lot of humanlike social behaviors, but not extensive cooperation and gossip.

          There aren’t many ape fossils from back then, despite a lot of “earlier than thou” competition among the paleontologists, but we tend to assume that the 5-6 million year creature looked and acted something like the chimp and bonobo.  Certainly, if you want to see a living, breathing candidate for what our ancestors used to be like, spend a few hours at a zoo observing a dozen bonobos.  The San Diego Zoo has an excellent exhibit and so does Planckendal (between Brussels and Antwerp).  Bonobos have more behavioral overlap with humans in some areas (using nonreproductive sex as a social tool, for example) – though there are other areas (such as ganging up five-on-one to cooperatively murder a neighbor) where, alas, we seem more like the chimps.

          Why the difference between such closely related species?  It’s probably nothing as simple as testerosterone levels but rather something more along the lines of social group size and structure.  Even though young bonobo females tend to emigrate to another band in the familiar incest-avoidance strategy, they develop strong bonds there with other females and generally tend to dominate over males.  Chimpanzee troops have much stronger “band of brothers” aspects.  Despite some hostility between bonobo groups, peaceful mingling often occurs; in chimpanzees, hostility between groups is the rule.

In evolution, new behaviors routinely precede the appearance of concrete adaptations that facilitate those behaviors.

- Alan Walker &
     Pat Shipman
, 1996. p.

          Upright stance seems to have caused the first major anatomical modification from the common ancestor (though some behavioral modification likely preceded that).  Whenever something major like that happens, there is often a whole series of new species soon thereafter, each somewhat different (it’s called an adaptive radiation in evolutionary biology, and it’s not unlike all the diverse web ventures of the late 1990s triggered by internet popularity, each trying to find a new niche to exploit).  So one expects to find a number of different hominid species back at 5-6 million years ago, trying out the new niches that upright posture opened up.  Most surely died out within a few million years or so.

          The initial stimulus for the upright rearrangement is unknown – maybe wading offshore, maybe carrying babies unable to cling to missing body hair, maybe foraging where the gathering had to be hauled home rather than consumed on the spot in the usual ape fashion.  Certainly upright locomotion per se is initially very inefficient but, once the knees and hips rearrange themselves, it’s probably an improvement on the knuckle-walking of the chimps.

          At about the same time, there was a loss of forest as climate cooled.  Unlike the other apes, our ancestors adapted to open woodland and then savanna, with all the attendant problems of competing for food with big savanna predators (and avoiding becoming their dinners).  Likely the transition from savanna (grasslands with scattered trees) to the treeless steppes was far harder, what with not a single tree to serve as a perch or refuge.

          Extensive Serengeti-style savannas didn’t develop in Africa until about one million years ago, although fossils of browsing and grazing species did start to increase by 7 million years ago.  Some lower-body characteristics of upright posture are seen by 5-6 million years ago, and all of the australopithecines seem to have lived near wooded habitats – or, at least, near the waterholes frequented by animals that did live in the woods.  There’s the occasional suggestion that there was a period when our ancestors might have waded among the flora and fauna near shorelines.

          By three million years ago, when more savannas developed in the Rift Valley, the story must have involved following river valleys deep into Africa and adapting to the grasslands that border the waterways and lakes, with major behavioral adaptations for making a living in a way unlike forest-dwelling chimps.  The widening and deepening Rift Valley likely helped to separate the chimp-bonobo species to the west from the bipedal apes of East Africa, in what Yves Coppens likes to call the “East Side Story.”  It perhaps gave them some room to develop separately, without competing constantly.  Indeed, some monkeys also adapted to the East African savanna about the same time, and competition from such “baboons” would have been a factor – just as competition from the local monkeys, who can clear out fruit trees far faster than chimps, is a major factor for the surviving chimpanzees of Uganda.  While the number of monkey species has been growing for millions of years, the number of ape species has been declining, proving that bigger brains aren’t everything.

          Our ancestors weren’t leaving around much evidence of stone toolmaking, though they were likely as clever with found-object tools as their modern chimp cousins, all those termite-fishing wands and nut-cracking hammers.  Their brains surely were functionally diverging from the chimp model, but their brain size was still in the great ape ballpark.  The australopithecine teeth suggest they were eating a lot more rough stuff than chimpanzees, and the males were twice the size of females (in chimps and humans, males are only 10-20 percent larger).  Both of these away-from-the-chimps trends reverse with the appearance of Homo about 2.4 million years ago.  The alternative to them reversing is that Australopithecines aren’t really our ancestors – that some other species with small teeth and less oversized males is yet to be found in the ancient layers between 6 and 2.5 million years ago.


Sometime this side of three million years ago, the climate drifted into the ice age jitters.  Both chimp and australopith populations were surely downsized and forced into refugia  (small isolated regions able to sustain the traditional way of life for a fortunate few).  The ancestor of chimps and bonobos likely had refugia on each side of the Congo River.  Within each refugia, they inbred and drifted and adapted to yield what we now see as the two surviving species, Pan troglodytes and Pan paniscus.  Something similar likely happened in East Africa to the australopithecines, yielding a new variant which, starting about 2.4 million years ago, had a significantly larger brain.  This was when we start talking of a Homo lineage with bigger brains (and with the cortical folds in somewhat different places, suggesting reorganization), unapelike inner ears, smaller teeth, and likely carrying around infants that were even more helpless at birth than are ape infants.  The males likely weren’t competing with one another for access to females quite as much as earlier.

          I won’t try to explain all of the species names that have been proposed for the first half-million years after the split.  For one thing, they change unreasonably often – poor old Zinj has been renamed more often than the telephone dialing prefix for London has changed.  But by 1.88 million years ago, Homo erectus is up and running – and running all over eastern and southern Africa.  And, indeed, into Europe by 1.7 million years ago and all the way to southeast Asia by 1.6.  It’s the first “out of Africa” for the hominid lineage, though we still know little of its details.

          By about 750,000 years ago, some new experiments were underway that led to Neandertals and modern humans, but Homo erectus persisted until about 50,000 years ago in China.  Erectus was the longest-running species in hominid history.

          Again, I won’t try to disentangle the spread of transitional species that led from erectus to sapiens over a half-million years (the period from 0.75 to 0.25 million years ago may be another adaptive radiation, like the earlier one from 2.4 to 1.9 million years), but by somewhere between 175,000 and 125,000 years ago, there were anatomically modern Homo sapiens around Africa.  They were in the Levant by 100,000 years ago (not surprising as the flora and fauna were often African).  Somewhere before 50,000 years ago, they spread out into the rest of Asia (and soon thereafter into Europe and Australia) in the most recent Out of Africa expansion.

          Did they interbreed with the indigenous populations they encountered (say, Neandertals or Asian Homo erectus)?  They surely tried when populations downsized and there wasn’t much choice in mates.  It has been difficult to find regional genetic markers in modern populations suggestive of “Neandertal genes,” though some regional anatomical oddities during the last ice age certainly suggest mixed ancestry.  This isn’t an argument about different groups of modern humans.  Everyone is related to everyone via common ancestors in Africa at that period; the issue is mostly one of how gradually the modernity transition occurred back in the last ice age.

          Since this last Out of Africa, some major regional attributes have developed from the immigrating Africans.  Roughly, they are now African, Asian (those that turned right after leaving the Middle East), and European (those that later turned left) – though mixed types abound from later population movements, blurring differences.

          And there is a lot of regional variation within each modern type, working against Platonistic “ideal” notions.  Variation in a population can make for strength in the long term, just as a mix of particle sizes is important in concrete and steel alloys.  There is far more variation within modern African Homo sapiens than there is within the Out of Africa groups.  Modern Africans really need the variation in reserve, just to work around the challenges from their parasite load and their fickle climate.  The Asians and Europeans, besides being less rich in genetic variations that they can tap, seem to have specialized somewhat toward one end of the parental-care spectrum, concentrating on relatively fewer offspring (their biology results in having fewer fraternal twins) who grow up more slowly (somewhat slower growth rates, later puberty, and so forth).


An important aspect of evolutionary history is the notion that there is a tree of species – and not, say, a web.  Even real trees occasionally have places where branches lean against one another for so long that they stick and fuse (an “anastomosis”).

          Hybrids are not always sterile.  Just imagine what it would do to the usual branching diagram of the higher apes if, for example, the chimpanzee lineage had been formed by a crossing of the gorilla and hominid branches.  Our assumption of binary branching, in effect, says that branches once established do not recross.

          This becomes a real problem when you know that hybrids are often fertile, as with crossings within modern human geographic groups. The history of “races” is full of such crossings and recrossings, a weblike history that makes one cautious of any treelike diagrams (Wisteria vines are more the model).  Europeans are a mix of Asian and African from many times and places.

          So comparing among the African-European-Asian “races” has its hazards.  If you just classified using skin pigmentation, for example, you’d lump peoples together differently than if you paid attention to skull shape and body proportions, the way physical anthropologists tend to do.  For example, the “European” skull shapes are found in both the fair-skinned Scandinavians and the dark-skinned people of the Indian subcontinent.  Evolution teaches us to expect a lot of small regional chance variations and adaptations, and we certainly see that humans are no exception to biodiversity.  But we are all, not very far back, black Africans.

          Already you can see that a lot more contributes to the hominid evolution story than merely stones and bones.  We have a hard time evaluating the evolutionary history of breath control, for example, so important for things like diving and speech.  Lots of soft materials like wooden spears didn’t survive very well (though there are now some from Germany that are about 400,000 years old, balanced much like the modern javelin).  We can now infer a lot about ancient climate and we’re getting better at piecing together what ancient behaviors might have been like.

          Maybe someday soon we’ll even see the step up to higher intellectual functions (syntax, planning, logical chains, games with arbitrary rules, structured music, coherence-finding) more clearly.  Intelligence was greatly augmented by the recent (maybe no longer ago than 50,000 years) evolution of higher intellectual function.  Did the abrupt climate changes give our ancestors some opportunities that great apes didn't get?


We’re now taking an espresso-and-dessert break, though I suspect that wine or beer would be a better therapy for the sore feet that tend to come with viewing the hard evidence via even harder floors.  We spent a lot of time discussing the so-called “bi-faces,” ubiquitous stone tools that are flat and edged, from chipping away on both faces.  Some have teardrop-shaped symmetry.  Indeed, they are not only hand-sized, but they look like a hand held palm-out, with fingers close together.

          A particularly fancy version is called the “handaxe ,” a term that has misled generations of researchers.  They’d fit into the palm of your hand like a discus (some are small enough for a child’s hand, others seem too large for anyone’s hand) but most would be rather awkward as striking and cutting tools because of having sharp edges all around (you’d think that they’d have learned not to sharpen them all around, were pounding their main use).  And no, they weren’t hafted, to fit into a handle of some sort.  As Richard Leakey once said of them, “embarrassingly, no-one can think of a good use.”  I’ll say something more about them when I get to Kenya.

          The restaurant here at the museum was designed to have a nice view of the Eiffel Tower, which is just across the Seine.  The tower doesn’t distract me a bit from thoughts of erectus ancestors.  But we’re looking down on a river.  And around the tower is a flat expanse, studded with grass and trees.  Compared to the surrounding city, it’s almost savanna.


If I ignore the regularity of the walks and plantings across the way, it reminds me of what my colleague Gordon Orians said about views that make people feel good.  As a behavioral ecologist, he speaks figuratively of the Ghost of Dangers Past (we dream of spiders and snakes, not current dangers such as cars and handguns).  He says our human aesthetic sensibilities are similarly influenced by the Ghost of Habitats Past.  Habitat selection by an animal is influenced by where it grew up, by where it sees others of its own species, and – especially when those criteria aren’t working very well – by some innate knowledge of what the species’ former habitats looked like.  There’s no reason that humans should be an exception.

          As E. O. Wilson likes to summarize Gordon’s results in his sociobiology lectures, a high-ranked vista for humans generally includes some water (stream, pond, seashore).  A forest view isn’t as good as one with some scattered trees (not too tall, either; trees that spread out in horizontal layers like acacias get higher viewer ratings).  A few large animals in the distance (but not too close for comfort) is an attractive option.  And, for best effect, the scene should be viewed from a slight elevation, preferably framed in a way that suggests viewing from some shelter.  The view from the restaurant qualifies.

          In short, I would conclude, it’s the view from a tree nest in our ancestral savanna home.  Such gut feelings tell us something about our ancestors – indeed about what they liked to put in their guts.  Such innate likings would have guided individuals in selecting a habitat suited to the better ways of making a living for their species, back then – telling them when to settle down, when to move on to “a better view.”

          Oriental landscape architecture adheres to this savanna-tree-house formula, what with that little shelter on the artificial hill from which to survey the ponds and scattered trees.  It’s species specific to us humans – a chimp or bonobo would have a different esthetic, likely featuring more of an inside-the-forest view of fruit trees.  They might find our open spaces threatening.

          But redesigning the Eiffel Tower area, to be even more like New York City’s Central Park (a nicely-designed open woodland with pastures and ponds), gets ahead of the story.  I’ll be in the Rift Valley soon, so let me save tree-house esthetics until then.  Maybe this belongs on the hominid bootstrap list, if we can ever figure out chimp esthetics as a basis for comparison.


So why did so many things change in the same five million years?  Some, of course, probably changed as a group, thanks to sharing some common neural machinery in the brain.  When you improve one bit of anatomy, you sometimes make possible another seemingly unrelated function.

          It’s much like when wheelchair considerations paid for curb cuts but soon 99 percent of their use was for things that would never have paid their way – baby carriages, skateboards, wheeled suitcases, bicycles, and so on.  Maybe one of those secondary uses will eventually pay for further improvements, but the “free lunch” is alive and well in both urban architecture and biology.

          For a local example of how shared-use structures can serve as a stepping stone to another specialized form, just climb the circular stairs inside the north tower of Notre-Dame and look around.  Back in the days before downspout plumbing, rainwater from the roofs stained the sides of buildings, so they invented horizontal rain spouts to carry rainwater a meter or so out from the side of the building.  Then they began to decorate the rainspouts with animal-like features – so they became multifunctional, good for both plumbing and as a prophylactic for warding off evil spirits.  From these shared-use versions, downward-looking gargoyles evolved, ones without rainspout functions remaining.  Then upright gargoyles evolved, perched on ledges and no longer looking like potential rainspouts at all.  The chimeras at Notre-Dame are particularly famous examples, from about 800 years ago.  And maybe our unusually-capable brains are too, from a somewhat earlier era.

          The higher intellectual functions (syntax, multi-stage planning, structured music, chains of logic, games with  arbitrary rules, and likely our fondness for discovering hidden patterns) may all share some neural machinery, as I have often discussed.  Maybe when you improve structured language, you get better at structured music “for free,” without having to have separate natural selection involving four-part harmony.

          Derek Bickerton argued, in our Lingua ex Machina book, that altruism needed some abstract mental categories for things like giver and recipient.  That could have helped set the stage for structured language.  And I argued there that the “get set” planning for ballistic movements like hammering and throwing needed mental machinery that would have found a secondary use in sentence structure, all those embedded phrases and clauses.  Once you can categorize for reciprocal altruism and plan for ballistic movement, maybe you can do the structured planning on different time scales, using the same parts of the brain to plan an agenda or a career.

          I think that this focus on shared neural machinery is far more useful than the usual bigger-must-be-better focus on brain size.  Everyone just assumes that bigger brains were a good thing and, while I think that’s likely true in some sense, I find myself playing the skeptic.

        Again, this is a game where anyone can play (though relevant knowledge always trumps speculation!), so have fun discussing it while I’m traveling and out of touch.  Another stop in Europe, and then on to Africa.


Notes and References
(this chapter
corresponds to 
pages 34 to 45 of the printed book)

Copyright ©2002 by
William H. Calvin

The nonvirtual book is
available from
or direct from
 University of Chicago Press

  Book's Table of Contents  

  Calvin Home Page

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