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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.
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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
1.57816°S   36.44417°E     1,000m ASL
                        Olorgesailie, Kenya
The easiest tool of all

We were driving along a nice, flat stretch of road, and I looked around to see that both sides of the road were flat for a long way back.  Aha, I said, drawing it to the attention of the expatriate cousin.  We are, I announced, in the midst of another former lake bed.

     Lakes shrink and expand as droughts come and go, so shorelines migrate.  There’s another kind of change, too:  most shallow lakes silt up eventually, if something doesn’t pull the plug before then.  That’s why it’s so flat here.  There’s a wonderful example to the west of Wilson Airport in Nairobi, a light-green-surfaced pond” with dark-green woods surrounding it – except that the “pond” now has a road running across it.  And it’s probably not a floating pontoon bridge, either.

     We’re on our way to visit Olorgesailie, which is right on the edge of a basin that held a lake until it lost part of its rim to earth settling.  About a million years ago, it contained Lake Olorgesailie (a quite large freshwater lake, over a hundred km2, now vanished), much like the still-wet ones in the Rift Valley north of Nairobi that we’ll visit starting tomorrow.  When you fly over this area southwest of Nairobi, you see a series of dry basins, each of which was once likely a big lake.  It almost looks like hillside terraces forming a series of modern rice paddies, cascading down to Lake Magadi.


I can’t view Olorgesailie without thinking of all the time that famous anthropologists have spent here.  Back during World War Two, Louis and Mary Leakey were largely confined to Nairobi by war duties and the petrol shortage, but they organized weekend digging expeditions down to Olorgesailie, about 90 km south of Nairobi on the Lake Magadi road in the midst of an acacia savanna.  They’d invite along their war-weary friends and put them to work, moving rocks.  Later in the war, some Italian prisoners-of-war helped out (one later became the warden of the national park created at the site in 1948).  Then in the early 1960s, Glynn and Barbara Isaac spent a lot of time digging here, leading to their classic monograph, Olorgesailie.

     Glynn Isaac had a dramatic way of lecturing about early toolmaking.  On the way to the lecture hall, he would pick up two fist-sized rocks from whatever offered locally.  He would place them atop the lectern and let the audience wonder what they were for, while he showed slides that introduced tools and their variety.  Then he would claim that the simplest sort of toolmaking would yield the most useful implement of all, the equivalent of the single-edged razor blade, handy for incising hides and amputating joints.

     He would put on his glasses, take a rock in each hand, turn his back on the audience, and begin hitting one rock against the other.  Chips would start flying toward the rear of the stage.  Glynn would keep this up until there were several dozen fragments scattered about.  There was nothing delicate about his technique.  It was just sheer brute force, with only enough sense of aim to keep from hitting the hand that held the target rock.

     Then Glynn would stop.  Silence, after the fury.  He would lay down the two remaining half-rocks and sort through the fragments littering the stage floor.  Ah-ha, he would say, here’s a sharp one.  Holding it up, testing its edge, he would proclaim it just the thing for butchering a zebra.  With it, you could take off a leg at the knee, then run away with dinner.  He would look at the remaining half-rocks and proclaim one of them good enough for defleshing – good solid rounded surface to grip, but still enough of an edge to hack away and separate skin from flesh.

     What more could you want?  And all from a minute’s unskilled work.  Well, you needed enough skill to prevent hitting your own hand.  But you could get around that, for a true beginner’s technique, by simply throwing a rock against a hard surface.  It was so simple that even an ape could probably do it.


Indeed, one can.  I once spent two lovely weeks in 1990 on the Portuguese coast discussing tools and language with several dozen diverse scientists.  Sue Savage-Rumbaugh was there, showing videos of what Kanzi the bonobo could do with words, and Nick Toth gave us a nice toolmaking demonstration on the beach.  One of the aftermaths of this Portugal meeting was that both Nick and I visited Kanzi in Atlanta, not long afterwards.  When Sue told me that Nick was going to demonstrate toolmaking to Kanzi, I told her about Glynn Isaac’s demo and joked that Kanzi would discover the beginner’s technique of brute force fracturing and sorting through the fragments.

     And that is indeed what subsequently happened.  Though Kanzi tried to imitate Nick’s more careful technique, he eventually threw the rock against the concrete floor and got a sharp flake that way, using it to saw through the rope that held shut the box with the food reward.  Sue then moved the scene outdoors where there was soft ground, to discourage this simple technique and try to get Kanzi to improve his rock-hammering technique.  He is now rather good at it; though still lacking a good hominid sense of “the right shape,” he can tell from the sound whether he has produced a flake which is sharp enough.  Thus at least one great ape is capable of the entry-level, what hominids were doing starting 2.6 million years ago.

     So the earliest tools weren’t even designed.  They were closer to found objects, though generated by a bit of banging around.  And that simple procedure yielded an enormous improvement in what could be eaten.


This probably wasn’t the beginning of meat-eating, of course.  Judging from baboons and chimps, there is a lot of opportunistic snatching of various small mammals (usually the defenseless young) who are hiding in the tall grasses.  And chimps are rather good at group maneuvers which trap small monkeys.  Chimps clearly love fresh meat and fat (the monkey’s brain is the most-sought-after prize).

     Though chimps will usually pass up a dead monkey left on a path for them to find, scavenging on the savanna has some not-so-obvious rewards that our ancestors might have utilized.  The bigger predators, such as the big cats, will eat their fill of soft parts, without chewing too much limb muscle (they too go after the fat first, both abdominal and periorbital).  The jackals and hyenas may take much of what’s left.  You’d think that there wasn’t much left for a hominid unable to drive off such fierce competitors.  But there is a lot of bone marrow, well hidden, if you just wait for the others to leave.  Hyenas have jaws strong enough to crush many bones, so they are your main competition for the marrow.  Throwing stones to drive them away is one possibility.

     Breaking open the long bones can be done by pounding hard enough to create a torsional fracture.  This opens up a length of bone shaft.  The marrow comes out looking much like a long pink sausage.  So this scavenging technique can make good use of the leftovers.  Just bring along a rock that is heavy enough – or, even easier, cut off the leg at a joint with one of Glynn’s sharp fragments and swing the leg like a club against a tree or a rock outcrop.  Amputating a leg also allows you to quickly carry the remaining meat and marrow to a safer place, away from the sharp-toothed competition.  The clublike fracturing technique can even be practiced high up in a tree, where heavy pounding is more difficult.  There are some archaeological sites that have an excessive number of long bones, complete with appropriate fractures.

     But once such basic discoveries are made, scavenging isn’t much of a growth industry.  You are still dependent on big cats and the hyenas to make your kills.  So in the familiar logic of food pyramids, your population numbers will always be limited to only a fraction of theirs.  Just as top predators are rare, so are top scavengers.  Is there a way of expanding prehuman meat-acquisition abilities, beyond that seen in chimps and beyond this “myeloscavenging” for marrow?

     Yes.  Surely several.  I’ll describe one after I do a little scene setting.  But note that tool use per se need not leave an archaeological record.


Olorgesailie shows the Acheulian toolkit that appeared about 1.8 million years ago.  It didn’t change very much for a million years thereafter.  In toolmaking, there didn’t seem to be any steady progress, contrary to our “Man the Toolmaker” expectations of what drove things.  The initial toolkit seen about 2.6 million years ago in Ethiopia had no more than a half-dozen tool types, and the Acheulian toolkit has no more than a dozen.  But in contrast to what came earlier, the Acheulian toolkit has at least one tool that looks “designed” (though for what isn’t clear).

     This biface is a rock that has been symmetrically shaped into a horizontal plane (some are so thin as to look like a frisbee).  But it isn’t round.  It looks somewhat like an arrowhead, bilaterally symmetric around a point.  Except the point isn’t sharp, and the back end isn’t hafted for a handle or arrow shaft.  Indeed the back end is often (though not always) sharp, just like the front and sides, sharpened by carefully chipping away at both faces.  When the back edge isn’t sharp, the name “biface” is usually applied and that’s perhaps the best name for all of them, given the current misleading nomenclature.

     As I mentioned back in Paris, the classic sharpened-all-around version tends to be called a handaxe.  The classic “Acheulian handaxe” is what you see at Olorgesailie by the thousands.  It’s like being on a cobble beach with lots of fist-sized round stones – except that most of the stones here were obviously reshaped by hominids who were obsessed with something.  Old lake beds in the Sahara, uncovered by sand dunes that shift sideways, can be similarly littered with handaxes.  There’s a dig at Olorgesailie which Louis Leakey called the “factory site” that testifies to the huge quantities left behind over the years.  But why?


Remains of zebras, monkeys, antelopes, giraffes, hippopotamuses, rhinoceroses, and elephants are all in the ground at Olorgesailie, which may suggest that past and present savanna habitats are very much the same. However, about half of the fossil mammals at Olorgesailie no longer roam the savanna; they are extinct. Their council included a frighteningly huge species of monkey, a large form of zebra, at least two inordinately bulky pigs, a disturbingly massive species of elephant, a few kinds of grass-eating antelope, and a heavier-than-usual hippopotamus.

     Everything we know about them indicates they were products of the Cenozoic decline, dedicated to eating grass. Their cheek teeth were large and specialized for chewing abrasive blades of grass and herbs.  Their bodies were larger than their ancestors’ and more massive than equivalent forms on the present savanna.  These anatomical facts mean that they took on the quintessential approach to the Pleistocene plains:  Eat grass, and eat it abundantly.  I tend to think of them as huge lawnmowers.

- Rick Potts, Humanity’s Descent, 1996



Notes and References
(this chapter
corresponds to 
pages 124 to 131 of the printed book)

Copyright ©2002 by
William H. Calvin

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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