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/Sterk.htm.
ISBN 0-226-09201-1 (cloth) GN21.xxx0
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William H. Calvin
University of Washington
are a series of hominid fossil sites in this beautiful valley outside
Johannesburg, now a World Heritage Site.
The most famous is the Sterkfontein Grotto, where the “Mrs.
Ples” australopithecine skull and endocast was found.
Most of the extracted fossils are now in a walk-in vault at the
Wits medical school in Johannesburg, where my wife and I spent the
It’s hard to say which was more impressive:
Phillip Tobias showing us the original fossil skulls and
comparing them feature for feature with chimpanzee skulls, or Ronald
Clarke and Kathleen Kuman showing us an ancient skeleton still in the
rock at Sterkfontein’s Silberberg Grotto.
In the vault, incredible variety and hard-earned detail. That natural endocast of the Taung child has amazing imprints
of blood vessels and the rounded hills and valleys on the brain’s
At Sterkfontein itself, first navigating a dizzying aerial
skywalk over the surface excavations, ducking under the wire grids
that hang over the area to provide a coordinate system.
And then scrambling into a dark cave, though several grottos,
and eventually coming to a handheld spotlight – showing several
figures huddled over a skeleton emerging from the hard rock.
There is likely a complete australopithecine skeleton embedded
in the rock at Sterkfontein. It’s
been there for about 3.33 million years, judging from the other animal
species found nearby. As
I noted earlier, most surviving skeletons from East Africa were buried
in mud, as a lake expanded and covered them up (or they drowned
offshore, failed swimmers). This
kept some of the bones from being trampled into fragments by herds
coming to drink. But the
Sterkfontein skeletons were instead embedded in very hard stuff, what
makes stalagmites and stalactites.
They are emerging very slowly as Ron Clarke uses the miniature
dental version of a jackhammer to remove the surrounding brecca grain
The foot of Stw 573 has already told a big story. While “Little Foot” is manifestly adapted for upright
stance and stride, with a heel more capable of weight-bearing than a
chimp’s, the big toe is almost as mobile as that of a chimpanzee.
So, despite Little Foot’s upright adaptations, the big toe
might have been of more help in climbing trees than a modern one.
The lack of transitional forms used to be a big objection to
Darwin, but with a lot of hard work, scientists are finding important
The transition to upright posture is still an unsettled issue
in paleoanthropology, as I mentioned when discussing the island
advantage. Upright posture is likely all tied up with the transition to
gathering and hunting (as opposed to the chimp’s eat-it-on-the-spot
and snatch-and-grab). There
are a lot of aspects to gathering (eggs, seeds, nuts, leaves, roots
– and the selection is greatly enhanced by food preparation from
soaking and pounding through to cooking).
Ditto for hunting (grabbing the defenseless young hiding in the
tall grass, surrounding in the chimpanzee manner, maneuver via
stampeding over a cliff, and projectile predation of many sorts).
Hunting is once again part of the overall explanation for our ancestral way of life, what with the evidence for eating a lot of grass by 2 million years ago. Grass, not leaves or fruit. We weren’t baking bread back then (which is the way we now ingest grass directly). No, some other animal probably converted the grass into meat on the hoof, and the hominids got the characteristic carbon stable isotope ratio from eating the grazing animal – they ate grass indirectly, at one remove. Had they eaten monkeys who in turn had eaten fruit, the bones would have the nongrass carbon isotope ratio instead.
It used to be that you couldn’t mention hunting without
someone undertaking to correct you.
(Phillip Tobias isn’t correcting me; he’s just
demonstrating another use of a hominid femur.)
If it wasn’t Lewis Binford’s minimalist approach to the
archaeological evidence back before cut marks were found overlaying
carnivore tooth marks on bones in 1979, it was someone saying that
gathering was far more important, that even in surviving
nonagricultural tribes, meat is only a small percentage of the
calories. Ditto for the
chimpanzees which hunt.
All quite true, so far as I know, though the Inuit are
obviously an exception, since they have very little to gather for so
much of the year. Indeed, gathering as more important had a certain attractive
logic to it. It seemed to
follow from the economistlike view of evolution, which is a common
misconception about the nature of evolutionary change.
So perhaps I should undertake to explain why everyday
importance is not necessarily what you want to focus on.
This will be heresy to some, old hat to others, but here goes.
oversold gradualism to some extent, in his effort to show that
there were ways other than catastrophic change for evolution to occur
(recall that nice algorithmic crank that I mentioned back at Down
House). This is an
Alice-in-Wonderland sort of principle (the Red Queen told Alice that
you have to keep running just to stay in the same place).
Certainly “automatic gradualism” is the lesson that people
most easily remember a week later, rather than Darwin’s nuanced
notions of evolution.
But there is really nothing automatic about evolutionary change, where everyday usefulness is automatically rewarded (and so you can remember a single principle rather than all those messy details). Biological adaptations can backslide, if not backstopped by speciation, just as cultural improvements are notoriously easy to lose (recall how the Tasmanians lost fire-starting and fishing techniques, once isolated from Australia).
More important, to my mind, is that many adaptations and
inventions don’t have growth curves.
If you invent a digging stick to expand the range of gathering
possibilities, there isn’t too much you can do to improve it into a
shovel until a lot of ancillary improvements occur in the creation of
sharp tools of the sort needed to make other tools.
To re-double your payoff in terms of calories gathered via the
digging stick takes a lot of further invention.
If you invent soaking to help remove the bitter taste from
plant toxins, it is again hard to double and redouble your payoff
until you invent boiling. Efficiency
improvements are often difficult.
The long stasis in rock toolmaking doesn’t surprise me a bit.
The same is true of most aspects of hunting. But one aspect of hunting, projectile predation, has an extraordinarily long growth curve because the distance achieved with accuracy can be redoubled so many times. No matter how many times you’ve improved your throwing distance, doubling again has additional payoffs in terms of how many days each week that your family gets high-calorie, low-toxicity meat. Furthermore, there may not be much to gather in certain commonplace climate transitions, and getting through the crunch and its aftermath may turn out to be far more important than everyday efficiencies.
Hominid hunting (beyond the chimp and baboon opportunistic
style) is now thought to go back several million years.
You can tell a lot from how much chewing had to be done. Gorillas have to chew fifty pounds of plant foods every day,
and their skulls have a lot of extra space to attach the muscles, all
those ridgelines down the middle and around the back. But in the Homo skulls, all that anchoring space
starts to disappear, as if chewing was no longer such a problem.
The cross-section of the jaw muscle can be gauged from the
space inside the zygomatic arch that goes from face to ear – I can
fit six fingers into the muscle’s space on my erectus skull
cast, but barely two into the same space on a modern sapiens skull.
Notice too the decreasing size of the teeth.
So, as was obvious even back in the
gathering-is-politically-correct days, there has been a big change in
diet since the time of the common ancestor with the chimpanzees and
bonobos. While cooking
– which has made life safe for vegetarians, because of a major
expansion in what plants can become food – is part of that story, it
may arrive late in the story, long after the major bony changes are
seen (although there is one important proposal that would place it
back at 1.88 million years when Homo erectus arrives on the
scene). Gorillas are
vegetarians and it has trapped them in a limited ecological niche that
requires fifty pounds of rough food every day, with gut length and jaw
muscles to match.
One food source, occasionally exploited by chimpanzees in the
more arid areas, is underground:
the underground storage organs such as tubers and other roots.
They occur only infrequently in rain forests but are found more
often in woodland on the fringes of forests, where herbs benefit from
storing water and nutrients during dry periods.
Most animals can’t eat them, as they are rich in toxins and
hard to dig up. Mole-rats
and pigs specialize in them, and their bones are found in association
even with 4 million-year-old hominid fossils.
Pigs are particularly interesting because their molar teeth
(whose size and enamel thickness tell you about diet) have a lot of
similarities to those of the australopiths.
At some point (the problem is when, early or late), our
ancestors learned how to exploit such roots as a fallback food when
their preferred foods were in short supply.
To extract them often requires digging and chopping.
They are improved by pounding and soaking, which involves a
degree of food preparation not usually seen in the other apes.
Cooking is even better. One
formulation has it that eating grazing animals goes back to 2.5
million years (there are butchery marks on the bones of large mammals,
back about then), and that cooking (or some other equivalently major
improvement in food quality) starts about 1.9 million years ago.
curves are where there is a payoff to repeated improvements.
If some brain enlargement is good (we usually assume), perhaps
a little more is even better. Curves
sometimes turn over, of course, why self-medication based on
more-is-better can be dangerous.
Physicians since Hippocrates have been warning about the
trouble that the more-is-better metaphor gets us into.
But upward growth curves are especially relevant when you have
something like abrupt climate change that can pump you up the curve.
When there isn’t much to gather, hunting temporarily becomes
rather important, even if providing less than 10 percent of calories
in other times – and one aspect of hunting, accurate throwing, has a
nice long growth curve.
civilized man ever reach these distant lands, and bring moral,
intellectual, and physical light into the recesses of these virgin
forests, we may be sure that he will so disturb the nicely-balanced
relations of organic and inorganic nature as to cause the
disappearance, and finally the extinction, of these very beings whose
wonderful structure and beauty he alone is fitted to appreciate and
enjoy. This consideration
must surely tell us that all living things were not made for man.
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