William H. Calvin, A Brain for All Seasons: Human Evolution and Abrupt Climate Change (University of Chicago Press, 2002). See also http://WilliamCalvin.com/BrainForAllSeasons/Paris.htm.
ISBN 0-226-09201-1 (cloth) GN21.xxx0
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William H. Calvin
University of Washington
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.
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 dot.com
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.
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
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.
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
(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
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,
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).
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
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
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
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.
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
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
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.
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
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
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
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.
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