Home Page || The Calvin Bookshelf || Science Surf magazine || Table of Contents
A book by
William H. Calvin
The Throwing Madonna
Essays on the Brain
Copyright 1983, 1991 by William H. Calvin.

You may download this for personal reading but may not redistribute or archive without permission (exception: teachers should feel free to print out a chapter and photocopy it for students).

Scanned, OCR'ed, and webbed -- but NOT proofread (14 Jan 97)


Woman the Toolmaker?

To the first maker of flints who forgot his dinner.

[Apes] are capable of perceiving the solution of a visible problem, and occasionally of improvising a tool to meet a given situation; but to conceive the idea of shaping a stone or stick for use in an imagined future eventuality is beyond the mental capacity of any known apes.
KENNETH P. OAKLEY, Man the Tool-maker (1964)

Because modern big-game hunters are male, it has long been assumed that the earliest hunters were also male--an assumption examined in an earlier chapter. A similar assumption has the creativity of early hominid males resulting in toolmaking, such as the sharpening of stones for their spears. But, as more time has been spent in studying primates in their natural habitats, many examples of invention and tool use have been observed. And the females usually play the starring roles.
      It all started in 1953 when scientists began studying a troop of Japanese macaque monkeys on the island of Koshima. Sweet potatoes were left out on the beach to attract the monkeys to a location where the scientists could observe them. An 18-month old female, named Imo by the observers, adopted a novel method for cleaning off the sand adhering to the surface: she would dip the potato into the ocean and wash the sand off. Soon Imo's playmates, and then their mothers, adopted the technique. Within several years 90 percent of the monkeys in the troop had adopted this cultural practice, with only the old males refusing to have anything to do with it. The scientists tried introducing caramels wrapped in paper. The candies were first sampled by the young, then by the more permissive mothers, and finally (after about three years) most of the adult males had also adopted the new food.
      In 1955, Imo again made a major invention. The scientists had scattered wheat on the beach. Picking it out of the sand, grain by grain, is rather tiresome. Some species of monkeys (such as the gelada baboons) are good at such tasks because they make their living by seed foraging in the plains; they also have evolved short forefingers to make it easier to pinch a grain between thumb and forefinger. Imo found a better way: She threw a handful of beach into the ocean (perhaps in a fit of frustration?). The sand sank, but the wheat grains floated. Imo scooped up the wet wheat and ate it--and thereafter repeated her performance whenever there was wheat available. Again the practice was observed and imitated by others, the juveniles being the most likely to adopt this new sifting method, the older animals being most likely never to learn the technique (they didn't mind the wet wheat, however, as they would plunder the juveniles', though never throwing it into the ocean themselves).
      This study not only illustrates innovative cultural practices in another primate, but it also shows who is most likely to imitate a new invention: the young. In general, the young are likely to be more inventive as well, being more playful (Imo was also perhaps young enough not to share the usual primate fear of water). Why might one sex be better at invention and tools than the other? Because mothers are around the young more than the males, they may be exposed more to new inventions. But other factors seem likely to be involved in female inventiveness. Perhaps they have more patience with a difficult technique (as we laboratory-bound scientists are only too aware, nothing works the first time--or if it does, it fails the next dozen times). Or perhaps the females just have inherited more relevant skills. None of these possibilities have been sorted out yet, but the natural behavior is telling some pointed stories.
      In the late fifties, when Jane Goodall began studying the wild chimpanzees on the Gombe Stream preserve in Tanzania, she noted that chimps would spend hours fishing for termites, especially the female chimps. This quiet, patient behavior was quite in contrast to the usual noisy, rambunctious assemblage of chimpanzees. A chimp would select a stick or twig of the correct thickness and length, strip the leaves off, and poke it down a hole in the termite nest. By withdrawing it slowly, a few termites might come along for the ride and promptly be licked off. Chimpanzees have been observed to strip such a twig, without a termite hill in sight, and then carry the prepared tool around for some time while searching for a suitable termite hill in which to use it, contrary to the axiom that only humans prepare tools in advance of need. Subsequent studies by William McGrew at Gombe Stream have shown that female chimps are much more persistent at termite fishing than males, though males start fishing about as often.
      The rest of the chimp story concerns nut cracking. Breaking open shells is practiced by many species. Birds, such as the Pacific gull, pick up shellfish and fly to a suitable height, dropping the shell over a rocky area (gravity as a tool, yet), and then descend to consume the innards. An interesting reversal occurs when the shell is too big to be carried aloft. In 1850, long before aerial warfare began, natives in South-West Africa told of how Egyptian vultures cracked open giant ostrich eggs by bombing them with rocks carried aloft in their talons. More recently, Jane Goodall and Hugo van Lawick have photographed this vulture actually throwing rocks at ostrich eggs: standing at short range, the vulture holds a rock in its beak and throws it with a strong downward movement of head and neck. But chimps take the prize: their technique for nut cracking is strikingly human.
      In 1843, J. S. Savage and J. Wyman noted that chimpanzees may use rocks to hammer upon shells, in an effort to crack them open. But subsequent observations of such hammering have been rare. In 1979, Christophe and Hedwige Boesch of the University of Zurich embarked on a study of the chimpanzees in the Tai National Park of the Ivory Coast (the neighboring tribes fortunately consider the chimpanzee sacred, an attitude which helps the chimps survive; if the American bald eagle were protected by religion or a taboo rather than legislation, it would be better off too).
      The Boesches concentrated on how chimps hammered open nuts--a frustrating task, because the chimps would run when ever they caught sight of the scientists. Out of 4200 hours in the field, the Boesches observed nut cracking for only 62 hours total. Often they would only be able to hear the nut cracking take place, staying at a distance and counting the hammer blows, learning to identify the sounds with the actual performance on those occasions when they could get close enough to see through the dense rain forest. When the animal left the site, satiated with nuts or scared off, they would be able to observe the chimp's sex and age.
      Chimps gather up nuts and then find a hard surface on which to place them, such as a rock or the root of a tree. They then proceed to hammer them open, using whatever rock or natural wooden club is handy. The nuts on the ground are quickly consumed, so the chimps climb the tree to collect more. The tree, however, is at least 15 meters high--the height of a 4-to 5-story building--and it is hard work just to bring back down a few nuts. The chimps reappear hauling all the nuts they can carry in a free hand and inside their mouths. Then they crack the Coula nuts open on the ground in the usual manner, again using whatever natural hammer is convenient. And then the long climb back up the tree for more.
      The hammering technique requires positioning the nut on the hard surface at the correct angle and then hitting it repeated times: first hard, and then softer and more precisely. Somewhat more females were observed using this simple gathering and hammering technique than males, but it was widely practiced by both sexes, by adults and adolescents, even by juveniles (and by one female infant!).
      The Panda nut is much bigger and tougher, about 5 or 6 cm long, formidable like a giant walnut. It has three or four almonds, but each is surrounded by a hard shell and sticky husk, plus the -thick outer shell. They are gathered and carried by hand to the nut-cracking workplace. Chimps place them on hard rock outcrops or in depressions in a tree root (probably created over the years by generations of chimps visiting the same tree and needing a good anvil). Sticks are too soft to be good hammers; only rocks are used. If no rock is lying nearby, the chimps will search for a suitable one, sometimes carrying it hundreds of meters back to the workplace. Powerful hits are required to initially crack the thick outer shell of the Panda nut; then a series of hits are precisely graded to crack the inner shells without shattering the almonds. The nut must be repositioned at least three times during this process.
      Over 95 percent of the chimpanzees observed to engage in this elaborate cracking process of the Panda nuts were females. And females were also virtually the only chimps to engage in the most skillful nut-cracking process of all: with the workplace high up in the tree, balancing precariously on a tree branch while hammering away at Coula nuts.
      Saving the round trip up and down the tall tree is all very well, but it does require some advance planning: a suitable wooden club or rock hammer must be selected and carried up the tree using one hand or foot. The chimp first gathers some nuts, storing them inside the mouth and carrying by hand as many as possible to a suitable workplace high in the tree on a broad branch. To crack the nut, one hand must be free for the hammer, and if the nut is to be kept from falling to the ground after the hammer blow, the other hand often must hold it. This means that the chimp has to rearrange the stockpile of nuts, holding them with one foot (this leaves one foot free for hanging on!) and inside the mouth. After the target Coula nut is cracked by repeated blows and repositionings, it is eaten--which of course requires that the stored nuts inside the mouth must first be transferred to another holding place. And then there is the hammer to worry about: it is often balanced on the tree branch temporarily. Finally, the chimp gets to eat its hard-earned almond.
      To hammer another nut, hammer and nuts are rearranged and the virtuoso performance repeated. When the working supply of nuts is exhausted, the hammer is sometimes left balanced at the branch workplace; other times, the chimp carries it along on the next round of gathering.
      About 92 percent of the chimps using the treetop workplace technique were females. And the only two adult males observed to use the technique are perhaps special cases: they were in the same tree as an estrus female and probably followed her there (when a female chimpanzee is sexually receptive, she is often followed around for days by several adult males). So the two most difficult nut-cracking techniques are practiced almost entirely by female chimpanzees. And the less difficult termite-fishing technique is practiced largely by females.
      Humans might deal with such nut gathering somewhat differently. If there were sufficient cooperation developed among the group, one member could climb the tree, shake loose some nuts, and then return to share the supply gathered off the ground by the other members. Or, lacking such trust, the human might use a carrying bag slung over one shoulder, picking a large supply in the tree and then returning to earth to find a less precarious anvil. The lack of either cooperation or carrying bag meant that these chimps developed treetop hammering skills that had the precision not to knock the nut off the limb or smash the fingers holding the target nut.
      Most speculation about the development of toolmaking has centered upon its relationship to hunting, though some tools (such as pry bars and hand axes) seem more likely to have arisen from gathering activities (digging up edible roots and grubs). In particular, precision hammering is usually associated with flaking rocks in order to make scrapers or hand axes, or to obtain flakes for sickles or arrowheads (flaked pebbles, probably for use as knives, have been found in deposits several million years old). But the chimp hammering techniques suggest that rock flaking itself could be an accidental by-product of nut cracking: the Boesches observed that chimps sometimes flaked stones while pounding the hard Panda nut. In three instances this happened to a granite rock and once to a quartzite one. And in each case, it was a female chimp who flaked the rocks.
      The data on the evolutionary origins of toolmaking are still thin, but the shoe is now on the other foot as regards which sex was the more innovative. The Boesches conclude their discussion of the flaked stones: "these chimpanzee-made artifacts suggest that such tools could have been produced by early hominids when they used stones as hammers during a gathering activity.... The skill of female chimpanzees at Tai suggests the possibility that the first human tool-makers were women."

The Throwing Madonna:
Essays on the Brain
(McGraw-Hill 1983, Bantam 1991) is a group of 17 essays: The Throwing Madonna; The Lovable Cat: Mimicry Strikes Again; Woman the Toolmaker? Did Throwing Stones Lead to Bigger Brains? The Ratchets of Social Evolution; The Computer as Metaphor in Neurobiology; Last Year in Jerusalem; Computing Without Nerve Impulses; Aplysia, the Hare of the Ocean; Left Brain, Right Brain: Science or the New Phrenology? What to Do About Tic Douloureux; The Woodrow Wilson Story; Thinking Clearly About Schizophrenia; Of Cancer Pain, Magic Bullets, and Humor; Linguistics and the Brain's Buffer; Probing Language Cortex: The Second Wave; and The Creation Myth, Updated: A Scenario for Humankind. Note that my throwing theory for language origins (last 3 essays) has nothing to do with the title essay: THE THROWING MADONNA is a parody (involving maternal heartbeat sounds!) on the typically-male theories of handedness.
Many libraries have it (try the OCLC on-line listing, which cryptically shows the libraries that own a copy), and used bookstores may have either the 1983 or the 1991 edition.

Email || Home Page || The Calvin Bookshelf || Table of Contents || End notes for this chapter || Continue to read next chapter