W. H. Calvin's THE ASCENT OF MIND (Preface)
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A book by
William H. Calvin
The Ascent of Mind (Bantam 1990) is my book on the ice ages and how human intelligence evolved; the "throwing theory" is one aspect.
   My Scientific American article, "The emergence of intelligence," (October 1994) also discusses ice-age evolution of intelligence. Also see Wallace S. Broecker, "Massive iceberg discharges as triggers for global climate change," Nature 372:421-424 (1 December 1994) and his "Chaotic Climate" Scientific American article (November 1995 issue).
AVAILABILITY is challenging.
Many libraries have it (try the OCLC on-line listing), but otherwise it’s strictly used bookstores (and German and Dutch translations).
The Ascent of Mind
Ice Age Climates and
the Evolution of Intelligence

Copyright ©1990 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).


Back when I was trying on various book titles for size, I was temporarily attracted by several that, valued advisors assured me, were not properly serious for a book on human origins. The Little Brain That Could rightly emphasized the ape-to-human bootstrapping of brain size. It nicely contrasted with The Cerebral Symphony, wherein I emphasized how human consciousness now works (here I consider how it evolved in the context of ice age climate changes -- generation-to-generation evolution of mind, rather than its minute-to-minute operation). But The Little Brain That Could might have been shelved in the wrong section of the bookstore -- and much as I would like to write for young readers, human evolution is a topic that requires the reader to have considerable experience with the world, a long attention span, and an ability to keep multiple possibilities in mind simultaneously -- all while retaining the child's intense curiousity about origins.
      Then there was Our Gain in Brain Remains to Be Explained. My advisors admitted that not many book titles can be sung in the shower, but wondered if that was really fitting and proper for the "greatest of mysteries." I was particularly attracted by Our Gain in Brain because, in My Fair Lady, Eliza Doolittle sings her famous line from the elocution textbook, the one about where it rains in Spain. And then the professor whispers in an excited aside, "I think she's got it!" Anthropologists and biologists know that, when attempting to explain what "caused" human evolution, such roles are invariably reversed. The professor tentatively starts with an excited whisper, "I think I've got it!" Whereupon a chorus complains, in a mighty refrain, that the matter still remains to be explained.
      That's science for you, though our perfectly normal disagreements are often misunderstood by journalists and exploited by a certain type of religious fundraiser. There is total agreement among the experts that evolution happened over millions of years, and that the apes are the group of animals out of which we evolved. But scientists haven't agreed on the exact course that prehuman evolution took -- the what, where, and when -- though hard-earned archaeological and fossil finds are sketching in the broad outlines. Nor can we yet agree on what drove it -- those pesky how and why questions. Like Darwin, we keep getting into conflict with those who advocate a simplistic view of the world; not noted for their knowledge of elementary anthropology or evolutionary biology, they prefer miraculous "explanations." Of course, back when few antecedents were discernible, the scientists of three centuries ago also relied on the miraculous -- but today, just saying "God did it" resembles peeking at the last page of a mystery novel, without savoring the buildup, climax, and explanation of all those incidents along the way. Even religious scientists tend to agree with the Greek philosopher Polybius who, in the second century B.C., said: "Whenever it is possible to find out the cause of what is happening, one should not recourse to the gods."

WHATEVER THE ULTIMATE CAUSES of ape-to-human evolution, there are surely multiple proximate causes. The bootstrapping potential of technological problem-solving (toolmaking, hunting, etc.) is often mentioned as a way of working up from the apes. Other kinds of cleverness might also work, such as the social problem-solving that affects reproductive success (the most formidable problem typically faced by a chimpanzee is to figure out what fellow chimps are going to do next). And climate change, besides biasing evolution in certain directions, also affects the rate at which other "causes" make progress.
      Each proposed cause -- even if true -- seldom convinces other scientists that it is more important than their own favorite candidate from the multiplicity. Even if you only try to explain the changes in brain, body, and behavior since we last shared a common ancestor with the chimpanzees, many things appear potentially important. And because human evolution only happened once, all of the happenstance of that seven million years can, by some stretch of the imagination, be held to be essential for the making of modern humans ("We wouldn't be human without it" goes that refrain).
      Worse yet, there are some seductively attractive processes that might have sufficed, given enough time, to do the job of enlarging the brain fourfold. Our gain in brain is certainly the most central, compelling "fact" of post-ape evolution (though that's largely because, until recently, it was about all that could be measured from fossil skulls). Size -- even relative size -- may not be the most important aspect (more on that later). But surely the most commonly noted brain-enlarging process since Darwin's day is "Bigger-than-average brains are smarter, smarter individuals survive better, therefore a bigger brain will evolve gradually."
      Good old compound interest reasoning, sheer intelligence bootstrapping itself, little by little. Physicists who make grandiloquent statements regarding life in the universe are particularly prone to such one-sentence summaries. But such "universal truths," rising above the messy details, are what science is supposed to be all about, right?
      Yet even if true (and I would caution that bigger-than-average brains aren't necessarily smarter-than-average), such reliable-sounding causes could well have been superseded, rendered totally irrelevant. Why? A fast-but-chancy track often preempts the slow-but-sure tracks in the evolutionary race for a new ecological niche. Like patent protection, the evolutionary inventor may be rewarded with a winner-take-all protected niche, so that even-better (but late-arriving) candidates are locked out for quite a while. There are also "windows of opportunity," such as the boom times when competitive rules are suspended. They are brief intermissions in the grind of ordinary times when interesting things happen. (I am reminded of them each time that I get bored with a play or concert -- and discover from the program that there are no intermissions, that I cannot escape gracefully.)
      Evolutionary explanations involve a lot of such messy details, threatening the grand generalities. Since the unique history is important, piecemeal answers are inevitable. Unfort- unately, a patchwork quilt of little correct explanations does not readily constitute one grand answer (and so the complaining chorus chants its refrain once more). We keep wishing for a sturdy framework on which to hang the pieces.

THERE ARE SEVERAL THINGS that I hope to contribute to the debate about human evolution through this book. Individually, each may seem a little mundane, hardly an obvious "antecedent to consciousness." But they do hang together in a way that helps explain how the more elegant human abilities might have emerged.
      The first is that where the rain falls is surprisingly important (and in Spain, it falls mainly in the mountains, not the plains). As droughts demonstrate, climate is fickle; "sudden death playoffs" can happen within a matter of a decade or so. Abrupt climate change makes versatility, often a virtue, a necessity. There were many abrupt shifts during the last 2.5 million years of fluctuating climate known as the Ice Ages, quite in addition to the slow advance and retreat of the continental ice sheets. That 2.5 million year period is exactly when our brains enlarged and reorganized beyond the ape standard, exactly when toolmaking became prolific. Given the greenhouse problems coming up, one might almost call those several dozen ice ages "the qualifying rounds."
      A second involves how hominids might have discovered hunting. I have touched on this in earlier books (and, in The Cerebral Symphony: Seashore Reflections on the Structure of Consciousness, elaborated on the spare-time uses of throwing's mental machinery, which is quite handy for augmenting insight, foresight, and language abilities). But here I emphasize how the projectile predator niche might have been invented and bootstrapped with the aid of toolmaking (I will even touch on something which an early reader nicknamed "the killer Frisbee").
      Third, I suggest that there is a three-part cycle of evolutionary alterations in body proportions. This cycle can be rerun, something like a college course that can be repeated for additional credit; it involves several different sets of genes that regulate fetal and childhood growth. One likely result of the selection cycle I propose is a bigger and bigger adult brain; another predicted result is a considerable fluctuation in adult height during ape-to-human evolution.
      That cyclical subscenario also illustrates that any explanation, to use a baseball metaphor, has to touch a lot of bases along the way. Any adequate explanation must propose a framework whereby we could have evolved from an upright-walking hominid with an ape-sized brain to the fully-human cave painters of the last ice age. My modest attempt at this is in the form of a multimillion-year scenario, paced by the cyclical subscenario and (during the last 2.5 million years) by the ice age rhythms. The bases one should touch are, of course, part of the explanatory problem. My selections overlap with those of modern anthropology while adding some nudges and constraints from climate and brain.
      While I naturally hope that my scenario will turn out to be correct in both outline and details, the more realistic aspiration is that it might demonstrate the breadth of explanatory power that theories need. The anthropologists' favorites of the last few decades are rather narrow. They are known via static images, like tableau in a museum: seed-eating, "Man the Hunter," home-base, "Woman the Gatherer," and scavenging. Not unreasonably, they tend to emphasize either animal behavior or "stones and bones."
      But R.G. Collingwood noted in 1939 that history "is concerned not with events but with processes. Processes are things which do not begin and end but which turn into one another." Each is a continuing development involving many changes; the drying climate that changed forests into savannah in East Africa is probably the anthropologist's favorite process. I hope to demonstrate that the harder-to-depict re-entrant process is particularly important (what goes out the front door is eligible to re-enter the back door, and take another pass through the transformation). Indeed, an adequate explanation of human evolution will need a wide range of processes (both re-entrant and one-shot) from ecology, climatology, developmental biology, evolutionary biology, immunology, and from my own fields, physiology and neurobiology. The people piecing the story together will probably come from ethology, primatology, developmental psychology, the cognitive sciences, philosophy, linguistics, systems modelers -- as well as anthropology. The correct portrayal of the prehuman path (if we ever agree on one) will probably be too multifaceted to state in one sentence, and so we will yearn for the good old days of "Bigger-is-smarter-is-better gradual Darwinian improvements." The story surely won't sound as elegant as "The Rain in Spain."

IT IS WINTERTIME IN SEATTLE as I finish this book. The relentless sound of rain on the roof reminds me of the incorrigible leak that again imperils my collection of Current Anthropology; the downhill path to disorder is threatening my view of the uphill record. But then the typically snowy nature of wintertime elsewhere in these middle latitudes is the fourth important "cause" of our brain boom that I have found so fascinating. "Think Snow" is a bumper sticker (much favored by waterlogged would-be skiers) which I would commend to those paleoanthropologists fixated on the tropics, as a slogan emphasizing a golden opportunity.
      I suppose that we could have quadrupled our brains without the virtues of winter, but I'll bet that it would have taken forever. So much brain enlargement in a mere 2.5 million years is awfully quick by the standards of evolutionary biology. Yet winter once a year, an abrupt climate change every few millennia, and an ice age every hundred thousand years will speed up things ever so nicely -- at least if you've got our kind of brain, rather than a bear's. Or so my story goes.


Seattle, Washington

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