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/Down.htm.
ISBN 0-226-09201-1 (cloth) GN21.xxx0
Available from amazon.com or University of Chicago Press.
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William H. Calvin
University of Washington
My specialty is the time when man was changing into man. But, like a river that twists, evades, hesitates through slow miles, and then leaps violently down over a succession of cataracts, man can be called a crisis animal. Crisis is the most powerful element in his definition.
-Loren Eiseley, The Night Country, 1971
You might think of the climate as a drunk: When left alone, it sits; when forced to move, it staggers.
- Richard B. Alley, The Two-Mile Time Machine, 2000
You signed up
for this, I trust, because you read my preamble, all about
seeing human evolution in the context of a bust-then-boom climate
episode, with scattered groups surviving the fiery population crash.
And like a phoenix arising from the ashes, going on to great
things (well, at least, us) after a sufficient number of
repeat performances, just one concentration and expansion
episode after another, pumping us up.
I’m starting this little tour at Darwin’s home, sitting
at a park bench under a magnificent oak tree that dates back to
Darwin’s time here. Five
years after returning from the voyage of the Beagle, Charles
Darwin and his young family moved from central London to a pleasant
country home about 16 miles to the southeast, near the village of
Downe. He lived here
forty years until his death in 1882.
No more voyages around the world, not even trips to the
Continent, but Darwin had correspondents everywhere, and sometimes
they showed up at his door.
And it was here at Down House that he raised pigeons, studied
earthworms, and dissected barnacles.
Here he sat, pen in hand, and wrote out his books that
provided so much of our modern understanding of how nature came to
be the way it is.
But only ten years ago, a scientific pilgrimage to Darwin’s
country home was remarkably difficult, unless you got directions
from someone who had been here before.
Only the most detailed guidebooks had a mention of Down
House, and then only in the fine print.
Get off the train from London at Bromley South or Orpington,
and the taxi driver, upon learning your destination, would knowingly
suggest that there were much finer country homes to visit than Down
House – clearly not understanding that it was Charles Darwin that
made Down House so important, not its gardens.
Arrive, pay off your I-told-you-so taxi driver, and you’d
find a low budget operation financed over the decades by the London
surgeons, with only several rooms restored to what they were like in
Darwin’s day, back before the place had been turned into a girls
boarding school in the early 20th century.
There were a few rooms filled with old-fashioned museum cases
laden with a dozen coats of paint, but most of the house was in sad
need of repairs and unsuitable for visitors.
And this for one of the great scientists of all time, not
just one of England’s greats.
Still, it was enormously inspiring to anyone who understood
the intellectual triumph of Charles Darwin, this chance to see where
he had thought it all through – his study with his microscope, his
chair by the living room fireplace, and his “sand walk” out
back, where he went for three walks a day to digest his thoughts.
Often, one supposes, Darwin sloughed through the fine English
rain, likely blowing in from the west after forming above the warm
Most people who think a little about evolution are wedded to the basic idea of gradual improvements in efficiency – and not much concerned with the origins of what was later improved (it was just “mutations“). Yet it was Darwin himself (a point omitted from even the modernized science exhibits at Down House) who first cautioned readers about getting fixated on efficiency, and who – at the same time – offered a route for invention. He noted that changes in function could be “so important,” that an anatomical structure improved for one function could, in passing, serve some other function that utilized the same anatomical feature. (Darwin’s example was the fish’s swim bladder serving as a primitive lung.) Novelties come from those nascent secondary uses, not from a bolt out of the blue, as a cosmic ray mutates a gene.
you haven’t seen Down House since the reopening in 1998,
there’s a lot more to see, thanks to much fund-raising by the
British Museum. It is
currently operated by English Heritage, which provides audio wands
to guide you through the rooms.
Next to Darwin’s study, there’s his billiard room, where
cause and effect operated on a simpler, more direct, level than it
does in biology.
Across the hall is the large dining room with its bay
windows; it was also the “justice room” where Darwin served as a
magistrate on occasion.
The now-rebuilt stairway to the upstairs leads you to a
series of former bedrooms, filled with modern exhibits about
Darwin traveled into London for scientific meetings, but
mostly he kept up an enormous correspondence.
His was something like the modern “home office” style of
working, that computers and communications are making possible even
for scientists without inherited wealth.
Darwin’s life shows you another style of doing science, one
without classes to teach or students to supervise, without grant
applications to write, one where piecing together the big story
operated alongside the careful dissection of barnacles, digesting it
all on yet another loop around the Sand Walk, carrying a great stick
which he struck loudly against the ground, making a rhythmical click
as he walked along with a swinging gait.
It’s when making your own third loop around the Sand Walk
(now pebble covered in the familiar English Heritage style, though
there are still some flints to be found) that you find yourself
wanting to tell Charles Darwin about all that has happened in the
last 130 years, about how he was right about Africa being the place
where humans happened. Then
you scale back your plans to something more suitable for the time it
takes to make several more loops.
I decide on abrupt climate change, since it shows how you can
have catastrophic gradualism.
things via catastrophes was seen then (as now) as a form of
style without substance. It
was simply too reminiscent of miracles.
Gradual explanations were to be preferred, if they could be
were to be avoided.
A nice algorithmic turning of the crank was, in comparison, a
thing of beauty – and Darwin found a wonderful crank via his
inheritance principle, where the more successful of the current
generation were the ones who generated more of the minor new
variants which future generations would test against their
on a successful theme was the name of Darwin’s game.
Darwin saw that the climate had changed many times -
he immediately offered some geological details to support Louis
Agassiz’s 1837 notion of an ice age – and he assumed that
animals and plants had to change too, to keep up with the times.
The variants more in tune with the new environment would
reproduce better, in turn spawning yet more variants around their
gene type (many variants, of course, are worse than their parents,
but they don’t reproduce very well, what with high childhood
mortality). So adult
body characteristics could track the climate, thanks to some
novelties proving to be heritable.
Efficiency improvements do, of course, result in the long run
in a “lean mean machine,” where many features not used for a
long time are stripped out as excess fat.
Until recent years, economists loved this view of things,
with all its improving efficiency – until it became so apparent
that it didn’t explain an innovation, only its subsequent improvement.
And in an economy dominated by market capture, where the
first to market may overshadow a better late arrival, innovation is
becoming much more important than efficiency.
It’s the “survival of the fastest.”
natural assumption, surely valid in some cases, is that
climate will change slowly enough for little improvements to track
climate over the generations – say, more and more upright posture
as the blister-like uplift of the East African highlands helped
convert forests into open woodlands and then savannas.
What I’d want to tell Darwin is that, just a decade ago,
the ice cores revealed that there have also been very abrupt climate
changes every few thousand years (on average; most are somewhat
irregular exaggerations of an otherwise minor 1,500-year climate
These jumps are superimposed on the better-known gradual
trends arising from variation in the earth’s orbit.
They are so large and so quick that a single generation gets
caught, forced to innovate on the spot – innovate behaviorally,
that is, since there is no time for anything in the gradual
And this provides a way around the lean-mean-machine
implications of traditional Darwinism.
Continuing to carry around a lot of useful-in-a-pinch
abilities is a good thing when, about once in every hundred human
generations, the climate goes mad for a while.
The variants that became lean mean machines didn’t survive
very well in the crunch.
Climate catastrophes are often mixed up with evolutionary
jumps (imagined macromutations and the like).
But when the climate catastrophes repeat so often,
then a little one-percent change each time can jack us up, producing
major changes in body and behavior in only a million years or so.
Darwin, I like to think, would have been intrigued by this
“catastrophic gradualism“ insight.
On to the NEXT CHAPTER
Notes and References (this chapter corresponds to pages 11 to 19 of the printed book)
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