William H. Calvin, A Brain for All Seasons: Human Evolution and Abrupt Climate Change (University of Chicago Press, 2002). See also http://WilliamCalvin.com/BrainForAllSeasons/Bockenheim.htm.
ISBN 0-226-09201-1 (cloth) GN21.xxx0
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William H. Calvin
University of Washington
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
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
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
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.
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
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
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
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
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
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
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
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
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.
modern human brain (below, shown to the same scale) is about three
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