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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
49.6°N      8.2°E 
                        Bockenheim, Germany

Subject:          Tracing our roots back to the Big Bang


I’m at a family reunion near Worms, in the German wine country.  And there is a winery in the family.  I have to give an after-dinner speech, and so must abstain from sipping the excellent wine.  I hope the Liebrich audience likes the following, because I mostly had this e-seminar audience in mind when writing it.  It’s a quick sketch of what happened when.

     [Clearing throat.]  The Liebrich that emigrated from Mannheim to Pennsylvania in the eighteenth century is about six generations back for me, on my mother’s side of the family.  Just as you have two parents, four grandparents, eight great-grandparents, 16 g-g-grandparents, 32 g-g-g-grandparents, so you have 64 g-g-g-g-grandparents.  Thus I have 63 more family reunions like this one, yet to attend.  For the younger people here, it is eight generations back.  That ancestor eight generations back represents only a fraction of one percent of all your genes.  You have 255 more reunions to attend, to give equal time to all your ancestors of 200 years ago.

     This is unlikely to happen, of course, because it is so rare for someone to have the energy and enterprise to organize an event like this [here I thank Dr. Winfred Liebrich of Berlin for organizing the affair].

     So, what was the world like, several hundred years ago in the year 1800?  The Napoleonic Wars were involving all of Europe, and the French had annexed this vineyard-rich left bank of the Rhine.

     We were almost totally ignorant of how the brain worked in 1800, with little advance over what the ancient Greeks and Egyptians guessed.  Medicine in general was primitive in 1800 (bleeding and purging were in fashion).  Not only hadn’t surgical anesthesia been invented yet, but doctors hadn’t learned to wash their hands and were spreading disease from one patient to the next.  However, vaccination for smallpox had just been invented by the English physician Edward Jenner in 1796.

     In the physical sciences in 1800, there was a remarkable scientist here in Germany called Count Rumford.  His is a case of emigration in the other direction.  Benjamin Thompson was born into a Massachusetts farming family, and worked his way up to European nobility.  His politics placed him on the losing side of the American Revolution, and so in 1776 he moved to England and eventually became Sir Benjamin Thompson.  It was later, when the Duke of Bavaria asked him to come to Munich to reorganize the army, that he became Count Rumford of the Holy Roman Empire.  He invented things from stoves to welfare systems.  A very versatile fellow, somewhat like Benjamin Franklin but considerably more abrasive.

     As a scientist, he predicted in 1797 that the cold water in the ocean depths had to be coming from Arctic latitudes, a cold deep counterpart to the warm surface Gulf Stream.  It’s a river under the ocean, flowing southward down near the bottom of the Atlantic; it plays a big role in our modern understanding of abrupt climate changes, as it causes the warm northbound Gulf Stream to fail occasionally.

     Twice as far back, in the year 1600, is sixteen generations away (for humans, a generation averages about a quarter-century).  If you claim Shakespeare as an ancestor, remember that your relationship is only 1 part in 65,000 and that any such genes might well have been lost by chance, so that you are only a relative on paper.  Such is the power of dividing by half every quarter-century.

Our genes may be immortal but the collection of genes which is any one of us is bound to crumble away.  Elizabeth II is a direct descendant of William the Conqueror.  Yet it is quite probable that she bears not a single one of the old king's genes. We should not seek immortality in reproduction.
     But if you contribute to the world's culture, if you have a good idea, compose a tune, invent a sparking plug, write a poem, it may live on, intact, long after your genes have dissolved in the common pool. Socrates may or may not have a gene or two alive in the world today . . . but who cares?  The meme-
complexes of
Socrates, Leonardo, Copernicus, and Marconi are still going strong.

-Richard Dawkins,
  The Selfish Gene, (Oxford UP, 1976

     Dutch opticians invented the telescope in 1600 and soon Galileo was busy reinterpreting the heavens – a risky business.  Giordano Bruno, the wandering monk who influenced Spinoza and Liebniz, was burned in 1600 as a heretic, for (among other things) speculating about life on other planets, much like scientists do today.

     Now let’s jump twice as far, 800 years back to the year 1200 when building cathedrals was in fashion.  By this time, hay had been invented, and storing grass for the winter made it possible for farmers to maintain large herds of cattle instead of slaughtering most of the herd every autumn.  That improved meat supply is credited with allowing substantial cities to finally develop in northern Europe, whereas they had formerly been restricted to sites nearer the Mediterranean.  It’s also the medieval warm period in Europe, but that’s about to end.  Already climate change is making life miserable in the American southwest with centuries-long droughts, and by 1300 Europe slipped into 550 years of the Little Ice Age.

     Skipping back 1,600 years takes us to the year 400, when the Roman Empire was falling apart.  It’s the time when the Huns destroyed Worms, just east of here.

     At 3,200 years ago, in the year 1200 b.c., we’re talking Old Testament times, complete with pharaohs.  Island cities, such as those on Crete, weren’t fortified then because sea-borne warfare hadn’t yet been invented.  We’ve skipped over those great centuries in Greece between 500 and 200 b.c. when Pythagoras inferred basic geometric regularities and musical chords, Empedocles talked of the survival of the fittest in evolution, when Aristotle, Plato, and Archimedes created the classical foundations of philosophy and science.

     At 6,400 years ago, we are back to the first cities.  Farming settlements had been around for 5,000 years to the east of the Mediterranean, but not real cities with a lot of specialized occupations far removed from agriculture, like tax collectors.  Written history goes back only 5,000 years, which is when writing was invented in Sumer to keep tax records.

     Going back 12,800 years ago lands us at the origins of agriculture and animal domestication. It is when the Mediterranean islands were first inhabited, suggesting sailboats at the least.  Things had been warming up out of the last ice age, starting about 15,000 years ago.  It had melted all the ice sheets in Scotland, and the Scandinavian ice sheet was down by half.  But 12,900 years ago was the time of a big surprise, around most of the world.  Suddenly, just in the matter of a decade or so, the climate flipped from warm-and-wet into the cool-and-dry mode, with temperatures plunging back to what they had been in the ice ages.

     Here in Germany, the forests disappeared and vegetation characteristic of modern Siberia took its place.  This lasted for over a millennium until, even more suddenly, it warmed back up again and the rains returned.  This down-and-up event, called the Younger Dryas, is only the most recent of dozens of similar flips between warm-and-wet to cool-and-dry, usually recurring every several thousand years.

     At 25,600 years ago, we’re back in the coldest part of the last ice age.  Needles made of bone had just been invented.  North of here was mostly ice: a giant mountain of it sat atop Scandinavia – that’s why northern Germany and Poland look so flattened – and another ice sheet sat atop Canada, as tall as a mountain range.  Sea level then was at its lowest, forty stories below where it is now.  But it is also the time of the cave paintings such as Lascaux, a period when our ancestors clearly had acquired a modern suite of mental abilities – they thought, and communicated, much as we do.  Earlier than about 50,000 years ago, we’re not so sure of that, even though people then had modern bodies and brain size.

     By 50,000 years ago, we’re back before cave art.  Behaviorally modern Homo sapiens (people like us) were in East Africa (this is when you start to see the first evidence of fishing) and by 40,000 years ago, they were spreading westward into Europe from somewhere in Asia, encountering the Neandertal peoples already living there on the ice age frontiers.  Shortly afterward, the Neandertals were mostly gone and people like us were the only hominid species left on earth, even spreading into cold, arid places where the Neandertals never lived.  Homo erectus was still in China but modern humans had recently arrived in Australia, showing that they had mastered water travel, to make it across from southeast Asia.

     Going back to 100,000 years ago, at least three hominid species were around.  People like us were, however, only in Africa or nearby (and all of the Liebrich ancestors had black skins, too).  Modern Homo sapiens had probably been in Africa during the last warm period in the ice ages, which started 130,000 years ago (this is when you see the first use of fireplaces as a centrally-located feature of encampments, suggesting some change in social organization).  The warm period lasted until 117,000 years ago, when things abruptly cooled, much as in the Younger Dryas – but it stayed down in the cool-and-dry mode.  Major ice sheets didn’t develop until about 70,000 years ago, perhaps helped along by a major volcanic eruption in Indonesia that reflected a great deal of sunlight back out into space.

     Doubling again, back to 200,000 years ago, and we’re into the prior ice age (they last about 100,000 years between major meltoffs, and there have been dozens of them).  People like us were probably not around then, just various large-brained but ruggedly built people with brow ridges.

     Back at 400,000 years ago, there were a variety of confusing hominid species called Neandertals and “archaic Homo sapiens,” not only in Africa but in Europe and Asia.  Homo heidelbergensis might be the variety which was our ancestor.

     At 800,000 years ago, the ice age rhythms change somewhat, the major meltoffs shifting for some reason from a 40,000 year interval to our present 100,000 year interval.  Among our probable ancestors, there is Homo antecessor in the Iberian peninsula and Homo erectus in Asia and Africa – but a variety of variants are starting to appear, some of which later led to archaic Homo sapiens and Neandertals.

     At 1.6 million years ago, Homo erectus is in both Africa and southeast Asia, and the smaller-brained australopithecines are also running around Africa (they die out by 1.0 million years ago, leaving Homo erectus the only hominid around).

     Back at 3.2 million years ago, there were only australopithecines (“southern apes”), and only in Africa.  While upright in posture, they only had a brain the size of an ape’s, about a third the size of our brains.  While upright, they were still living pretty close to trees.  But momentous things are happening, as the earth is about to enter the ice ages after millions of years of a cooling and drying trend that has started to create savannas in Africa’s Rift Valley.

     North America and South America were not connected back then, and tropical ocean currents could still flow between the Atlantic and the Pacific Oceans in what I like to call the Old Panama Canal.  But Panama rose out of the seas, slowly damming up the passage.  By about 3.2 million years ago, the ocean currents were forced to rearrange themselves in a big way.  That seems to be the best candidate for the final event that tripped the ice ages, which began in earnest between 3 and 2 million years ago.  That’s when the Homo lineage split off from australopithecines, brains got bigger, and toolmaking started in earnest.

     Now we’re back to 6.4 million years ago, and that’s about when we shared a common ancestor with the modern chimpanzees and bonobos.  The hominid lineage split off then, and was already upright in posture at about 6 million years ago.  Bipedal apes, no less. We’re really the third chimpanzee, as Jared Diamond likes to say.

     Going back to 12.8 million years ago, we’re near the common ancestor with orangutans (gorillas split off in the meantime, about 8 million years ago).

     Back to 25 million years ago, apes evolved from the Old World Monkeys.

     And at 50 million years ago, we’re all still monkeys getting larger after the big extinction at 65 million years ago which killed off the dinosaurs.

     At 100 million years ago, we’re some lower form of primate, no larger than a squirrel but smarter.  Dinosaurs rule the earth, not our ancestors.

     Around 200 million years ago, we’re early mammals, even smaller and less significant, trying to survive the Permian extinction.

     Back at 400 million years ago, our ancestors are just venturing out of the sea onto land as some sort of lungfish or amphibian.

     At 800 million years ago, we’re in the Precambrian, and all the evolutionary action is still in the seas and very small.  It’s multicellular by now and looking quite weird when hard enough to fossilize.  A truly shocking event happened to the earth’s surface several times about then: it froze solid, from north pole to south pole, white all over.  Volcanos peeked through, however, and their carbon dioxide provided the greenhouse gases that eventually rewarmed the earth and melted back the ice.  Life in the sea wasn’t entirely frozen, as there were surely hundreds of pockets near the volcanoes which remained above freezing.  This isolation was one of the setups for the great Cambrian explosion of life that occurred 530 million years ago.

     Around 1.6 billion years ago, sex was being invented as a way of improving on bacteria-swapping genes occasionally, the primitive gene-mixing mechanism.  A new committee of cell parts had evolved, called the eukaryote, with the genes kept in a bag in the middle of the cell, called the nucleus.  This advance beyond the bacteria was momentous, allowing cells to be much more complex and capable.

     But back at 3.2 billion years ago, there were only bacteria-like cells around, no committee-like cells at all.  Life evolved 3.8 billion years ago in the oceans and around hot vents.

     Go back 6.4 billion years ago, and the Earth didn’t even exist  (it coalesced at about 4.6 billion). At 6.4, our ancestors were just dust swirling around in space, fragments of a star that had exploded.  Our “local supernova” about 7 billion years ago produced nearly all of the atoms presently in our bodies, cooking the heavier ones out of the hydrogen and helium that had been around for a long time.

     Double the time again and we’re back to the Big Bang at 13 billion years ago, not even atoms and molecules but just the very hot “quark soup” of the more primordial building blocks.

     And you can’t go back any further than that.  So far as we can tell, that’s when Time Began.  That’s when all the parts were put in place that eventually became Liebrichs (and bacteria and plants, too).  So that’s the beginning of the family tree, and the end of the talk.


After the family reunion broke up the next day, each car departing with a case of wine in the back, we sat in the shade talking about my departure the following day for Africa.  My cousin with the vineyard got to asking me questions about brain size.  Did the Homo erectus brain really increase in a stepwise fashion, he asked via our weary interpreter, or was it gradual?  Maybe a series of small steps, I answered, hedging.

     And was it really true that brain size increased to make us more intelligent?  It would be so easy to nod agreement.  It’s the conventional wisdom, the current default answer.  It’s probably true.  And I cannot confirm the opposite, or say that brain size was really about something else.  He’s not in the field and sensitive to nuance, nor the student of the subject that this e-seminar tends to attract.  But he’s an intelligent man and deserves a better answer than “Ja.”

     There are great costs, I said, to increasing brain size.  Our present brain is only 2 percent of the body by weight, but it accounts for 16 percent of the basal metabolism (the brain share is 3 percent in an average mammal, and some marsupial brains get by on less than 1 percent).  Were our brain only a third its present size, it would take a lot less blood.

     All of that additional blood flow had to come from somewhere in evolution, and some think that it was only after some high-calorie meat was added to the diet that gut length could decrease and free up some capacity.  Another expense is that bigger brains take longer to grow up.  They also decrease the efficiency of upright walking because of the birth canal size spreading the hips and promoting a return to the chimpanzeelike waddle.

     Yet I’m not sure what’s on the positive side of the balance.  Yes, brain size increase could have been for intelligence in general.  But something doesn’t fit yet.  So I’m not at all sure what bigger brains have to do with hominid evolution.  I find myself asking questions like:

·   Was the size increase really required?  (In the sense that a chimp-sized brain couldn’t possibly manage all those augmented functions like syntax, not any more than you could run Windows programs on a 1950 desk calculator.)

·   Or was it simply permissive?  (In the expanding-economy sense, that it’s easier to experiment with chancy new functionality if you don’t, at the same time, have to compact or eliminate some existing function.  These days, that’s what is blamed for “RAM bloat,” the escalating RAM memory requirements for new versions of software.)

·   Or was brain size, per se, not involved at all? (Except as a minus.  Size could just be a byproduct – reorganization of the brain might be the main thing, and the genes for reorganization might have had the side effect of increasing size at the same time, not being versatile enough to hold size constant while rearranging things).  Or size and reorganization might have been late secondary consequences of something like bipedalism’s rearrangements of body and brain.

My guess, for what it’s worth, is that brain reorganization could proceed more easily in the bigger-brained variants of any generation, just because of more room to maneuver – but that size per se wasn’t the name of the game.  There were certainly no new modules tacked on to human neuroanatomy that the great apes lack, not so far as we can tell.  However the brain is doing language, the areas involved seem to have “kept their day job,” as the psychologist Elizabeth Bates likes to quip, while doing language as a second job.  The same thing likely applies to those areas at the bottom of the frontal lobe which seem to have acquired the ability to maintain mental checklists and monitor progress on an agenda.  

The bonobo brain (top) is about the same size as brains of the bipedal apes, such as the australopithecines.  

The modern human brain (below, shown to the same scale) is about three times larger, 
with more than four times the amount of neocortex surface area. 
(Photographs thanks to Terrence W. Deacon)


Notes and References
(this chapter
corresponds to 
pages 46 to 58 of the printed book)

Copyright ©2002 by
William H. Calvin

The nonvirtual book is
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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