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/Soss.htm.
ISBN 0-226-09201-1 (cloth) GN21.xxx0
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William H. Calvin
University of Washington
gone from part of the Kalahari Desert, the part with a lot of water
passing through and evaporating in Okavango Delta, to a more typical
desert farther to the west, one with ephemeral streams lined with a few
trees – and almost none elsewhere.
It’s a savanna strip.
Admittedly, this was a good year for rainfall, but even when it
is much drier, the oryx, eland, and springbok (you really have to see
the youngsters’ jack-in-a-box act to appreciate the name) thrive here
on the valley floors among the sand dunes.
When you fly low over the area, you see a series of dark lines
stretching across the light desert floor.
They are dry watercourses.
There is still some water beneath the surface and, even if there
isn’t, the nearby plants are good at storing water for the rest of
the year. The leaves of
some plants can be crushed and wrung out like a washcloth, yielding a
surprising amount of water.
When the South African paleontologist Elisabeth Vrba told us
that there were a lot of new species of antelope appearing back about
2.7 million years ago in southern Africa, one of its prime implications
was that it indicated a need to adapt to arid environments.
And today, there are amazing numbers of oryx and the even bigger
eland here in the Namib Desert, happily grazing.
There are some small antelope that can forego visits to the
waterhole entirely, getting enough water from the leaves they eat.
If we could test antelope for landscape esthetics, they’d
probably prefer to look at something like a bush airstrip – a cleared
area where predators can’t hide.
And so bush pilots coming in for a landing have to first buzz
the airstrip, to chase them away.
It makes me realize how much meat on the hoof there was for our
ancestors to have exploited in arid environments.
If the antelope and the desert elephant hereabouts can adapt to
the desert, then they may make it possible for their predators to do so
as well. They just have to
patrol the strips, like teenagers cruising those urban strips following
highways out into the countryside. All
the resources are along a track, and it’s just back and forth.
The fauna associated with the small-brained australopithecine
fossils indicate a wooded environment; they wouldn’t have liked it
here. The later versions
called Paranthropus between 2 and 1 million years ago were
sometimes found in wetland environments, as were the earliest Homo
species. It’s Homo
ergaster/erectus and later species that are found in extremely arid
and open landscapes like this. It
seems pretty clear what they were eating; certainly in South African
coast archaeological sites, there are a lot of eland bones.
place is a desert because, at these southern latitudes, the
rains come from the east. And
by the time that they have traversed the whole width of Africa from
east to west (we’re just inland from the west coast), it is even more
of a rain shadow than Botswana’s Kalahari Desert.
Namibia is one of the driest places on Earth.
Indeed, what moisture Namibia gets often comes from dew, thanks
to the fog drifting in off the ocean, much the same as in the coastal
regions of Peru on South America’s west coast.
And there is fog here because the cold Benguela current offshore
causes the sea breezes to drop below the dew point as they blow in over
the cold current.
This cold current is part of the developing story
about how ocean currents and winds rearranged themselves just before
the ice ages started. Strong
winds often sweep surface waters aside – I’ll get into the subject
when I fly home over the North Atlantic and discuss the conveyor belt
for salt and heat – and bring deeper waters to the surface.
Deeper waters are cold; they’re also loaded with nutrients,
and so when they get brought up near the surface where sunlight can
penetrate, they serve as fertilizer for all the sea life offshore, a
whole food chain worth (lots of seals and dolphins and fishermen
Well, at drilling site 1084, less than an hour’s flying time
west of here, the surface waters are about 10°C colder now
than they were 3.2 million years ago.
That means some stronger winds have developed in this part of
the South Atlantic Ocean. The big changes were between 3.2 and 2.1 million years ago,
in the second half of the Pliocene, just before we start talking about
the Pleistocene’s ice ages. They
go in lockstep with the changes in the North Atlantic. It’s all part of the story about how the ocean and
atmospheric circulation rearranged themselves, to plunge us into the
fickle climates of the ice ages. Which
we are still in.
to prepare you for hominid fossil country (my next stop is South
Africa’s caves, then Kenya’s Rift Valley), let me suggest reading
an account of how hominid fossils have been found.
I’m particularly fond of Alan Walker and Pat Shipman’s The
Wisdom of the Bones which contains the following account of how the
first australopithecine came to scientific attention in 1924 and how it
was mostly ignored for the following decades.
I always tend to think of the Leakeys’ 1959 discovery of Zinj
at Olduvai Gorge as the first hominid skull discovery, but it was only
the first in East Africa (and in a stone-tool context).
The Taung skull was actually discovered a quarter-century
earlier by workers in a South African quarry, but dismissed by experts
as some sort of ape:
is a classic story of anthropology, all the more engaging for being
true. With unerring
timing, the box with the missing link in it turned up as [Raymond] Dart
was dressing, in wing collar and morning dress, to serve as best man
and host for a friend's wedding. The
men from South African Railways who staggered up to the house that
summer day in 1924 left two large crates blocking the stoop shortly
before the guests were to arrive. Dart had them moved to the pergola,
where they would be out of the way, and left off dressing to find a
crowbar to pry them open. The
contents of the first box were uninteresting scraps of fossil eggshells
and turtle scutes (the bony plates that underlie the turtle's shell).
On the top of the rubble that filled the second crate, Dart
spied an extraordinary thing: a natural, fossilized cast of the brain
– an endocast. It was of some creature whose brain was about as big
as that of an adult chimpanzee. From
his work with Elliot Smith, Dart immediately recognized that this was
no ape endocast (unparalleled as that would have been), but one with
distinctly human anatomy. He
rummaged through the box frantically and found a piece of bone, covered
in rock, into which the endocast fit.
And then real life intervened.
The groom appeared, anxious that Dart should brush the dust off
his suit and struggle into his stiff collar; the wedding party was
arriving momentarily. Dart took these two precious pieces of our ancestry and
locked them in his wardrobe, reluctantly abandoning them until the
festivities were over. . . .
Dart's precious find was not only overshadowed [first by the Piltdown hoax and then by Peking Man], it was literally abandoned – left, in its humble brown-paper-covered box, in the backseat of a London taxi by Dart's wife. It was recovered only after frantic searching. Dart gave up on plans to publish a monograph and returned home, discouraged and defeated. He gave up fossil work for many years and subsequently suffered a nervous breakdown. For years, the Taung child sat, forgotten, on Dart's colleague Gerrit Schepers's desk at Wits. . . .
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