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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).
  • Powell's Books in Portland lists used copies in their web database.
  • All chapters are webbed.
The Ascent of Mind
Ice Age Climates and
the Evolution of Intelligence

Copyright ©1990 by William H. Calvin.


Table of Contents

     Preface xv

Discarded titles such as The Little Brain That Could and Our Gain in Brain Remains to Be Explained.

Tracking Climate Change and Human Evolution
Abrupt climate change, not a gradual rise in sea level, is the most threatening aspect of the greenhouse warming: the North Atlantic Current seems to have suddenly turned off its warming and watering of Europe on more than 20 occasions during the last 120,000 years. Though happening as quickly as a drought, these changes last for centuries, even a thousand years in one case. Were that to happen again, 500 million Europeans might want to move elsewhere, quickly. Yet we humans thrive on such challenges: the fickle climate seems to have pumped up our brain fourfold larger than the ape-sized brain -- and that was all walking-upright hominids had, back before the ice ages started 2.5 million years ago. A key aspect of the pump: massive ice sheets create unusual population booms when they melt.

Smart, clever, intelligent: some gradations of learning, insight, and plan-ahead. The Search for Extraterrestrial Intelligence meeting at Lake Balaton, Hungary -- and the search for intelligent life back home on Earth. Why are there so few branches of the tree of animal species that have the cleverness of apes and humans? Dead ends? If being intelligent is such a good idea, why haven't more animals achieved it? Getting-better-and-better adaptations vs. evolution's sudden sidesteps. Rapid things sometimes occur in evolution, despite the gradual pace of changes in animal bodies: Compounding mechanisms for novel combinations. The "Baldwin Effect" and how behavioral innovations tend to precede anatomical change by natural selection, as in the case of flying squirrels. And behavioral change benefits from Darwin's "conversion of function in anatomical continuity." These jumps in function are pure invention, not just shaping up for more efficiency. Is more-than-the-apes intelligence another conversion?

How Climate Pumps Up Complexity.
Three things all started 2.5 million years ago: the ice ages, prolific toolmaking, and the unprecedented rate of growth in brain size. Which is cause, which effect? The role of "fast tracks" in sorting out multiple routes to big brains. Mama Bear and the two baby bears that don't live happily ever after: the massive overproduction on which natural selection acts. Sexual selection. Mutations versus permutations. Life coming ashore, thanks to major climate changes twice a day shaping up intertidal species. Decade-long cycles producing droughts: El Niño and La Niña. The "rules are off" periods of rapid diversification after a new niche is discovered and there is food even for individuals with rare anatomical variations. The tendency of rapid evolution to take place in small populations isolated from the main population of the species, and the tendency of climatic changes to create islands and then reconnect them.

Some Consequences of a Fickle Climate
Surveying the homes of Neandertals and early modern Homo sapiens while flying from Budapest to Copenhagen. Glacier-scoured mountains of Central Europe where archaic Homo sapiens have been found. The plains of Poland where, unlike Hitler's eastward blitzkrieg, early modern types slowly swept westward and displaced the Neandertals 40,000 years ago. Archaic Homo sapiens and its ancestor, Homo erectus. Robust and gracile australopithecines vs. Neandertals and early-modern Homo sapiens: why both heavyweights and lightweights? Juvenilization as a response to boom times; the hard life of Neandertals. Population booms on the frontier when ice melts back cause the frontier-type prehumans to become dominant. But the ice again advances, pushing the new population south, into competition and interbreeding with tropical hominids. In this way, a minority becomes a majority. This demographic pump spreads essential-in-winter genes, such as those facilitating hunting and fire-making, around the tropics.

OVER THE POLE: Surveying the Ice Ages from a Seat in Heaven
Flying from Copenhagen to Seattle, one sees the land of the two dozen ice ages. Changes in the Earth's orbit and tilt: Milankovitch's prisoner-of-war project. Cold spikes during warming periods: lessons from the Younger Dryas and similar cold snaps during the last ice age. Why Greenland wasn't named Iceland, and vice versa; the century-long changes in Atlantic climates. Whole continents may suddenly open up to habitation, as when big game hunters discovered the Americas, via the ice-free corridor just east of the Rockies. The salt economy of bays and the conveyor belt for salt linking the Pacific Ocean to the Atlantic's warming of Europe.

Growing Up in a Boom Time
Eunice Lake's alpine newts that never grow up; backing up in evolution via juvenilization. Climates that switch back and forth, causing genes to switch. Tooth size reduction in the most recent ice age, associated with more cooking and more pottery; relaxed selection for robust bodies or just juvenilization with "domestication"? The junk-food baboons; earlier maturity in humans when move from farm to city. Proximate versus ultimate causes, r-to-K spectrum of parental investment in offspring. New behaviors emerging from the "racial memories" of boom-times in the past: the r-shifting seen in improving conditions changes population averages in many ways. Concealed ovulation and sexual selection in hominid evolution.

WHIDBEY ISLAND: Ratcheting Up Brain Size

Parts, Process, Product: the legislative process illustrates a transformational process at work, and illustrates what a detailed understanding of human evolutionary processes might involve. Beach walk to an old Indian fishing village buried by a mud slide on Whidbey Island. And a mother-and-unborn-child burial. Relatively big heads occur with early puberty. Then stature re-enlarges in other ways. When the resulting big heads kill their mothers, there is selection for slower-than-average body growth rates, so the survivors are born premature-looking. Given selection pressure resulting in juvenilization, one gets a cycle that can be repeated many times to enlarge the brain fourfold.

HAND-AX HEAVEN: The Ambitious Ape's Guide to a Bigger Brain
A possible advantage of juvenilized bodies for throwing ability and thus hunting. How an ape could have invented the predatory throw, using side-of-the-barn accuracy. And how it ought to lead to something like the Acheulean hand ax. A heaven for used hand axes, in the Pluvial ponds of the Sahara. The growth curve for throwing, and the brain reorganization it demands.

SAN JUAN FERRY: Does Consciousness Emerge from Cortical Consensus?
Taking a rumbling ark through the San Juan Archipelago. Brain reorganization; we are more than a juvenile ape. The characteristics of consciousness, the uses of Darwin Machines, and how a consensus of cortical association areas might be what gives us our unitary sense of self.

FRIDAY HARBOR: Is There Intelligent Life on Earth Yet?
The eruption of Mount St. Helens. The Hoyle Memorial Symposium and the "supermind" of small scientific meetings. Raccoons prowling the tide pools. Midnight at Friday Harbor and the aurora borealis. Need for physiological understanding of population pressures, and the use of big computers to model the modes of regional climate, as the next steps in human intelligence that extend our abilities to think before we act. The ice-age "qualifying rounds" for the main event. Is Captain MacWhirr in command?

End Notes

If there is no translation for your language, complain at a relevant publisher and point them toward my literary agent:
Brockman, Inc., 5 East 59th Street, New York NY 10022 USA.
fax +1(212)935-5535 ....... e-mail john@brockman.com

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My twins are out:
How Brains Think
(Science Masters), a Book of the Month Club Selection,
The Cerebral Code
(MIT Press)
are now in US bookstores.
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