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The arrival of the Mighty Hunter
Next came the Mighty Hunter, Homo erectus. During his
reign, the big cats and the last of the Australopithecenes
vanished. And H. erectus took over the whole of 
His brain had grown to about half the size of
ours; around 750 cc.
H. erectus were
true people of the plains. We’ve talked
about our earlier ancestors being able to walk.
But there’s all the difference in the world between being ‘able to walk’
and being ‘a true walker – and runner’.
And H. erectus was the latter.
They had sacrificed their tree-climbing skills, by
acquiring long straight legs and arms.
No doubt there were many other adaptations as well. As a result they were no better climbers than
we are. H. erectus also acquired a small pelvis, a major cost as we’ll see
shortly.
As far as I can see, only one decent skeleton has been
found, of early H. erectus
anyway. It’s of a boy, ‘Turkana
Boy’. He was only 11 or 12 years old
when he died, but he was already nearly 5½ feet (1.6 metres) tall. The skeleton below comes from ‘Research Penn
State’.
But there was a more important sacrifice than mere
walking ability. Our 
earlier
ancestors had retained the large pelvises of their ape forbears. This means that their babies were born in a
far more developed state than ours are.
But a large pelvis is incompatible with good walking. So it had to go. H.
erectus babies were born as helpless as ours are, with the brain continuing
to grow considerably after birth, just as ours do.
This has considerable implications for the way they
lived. It’s difficult to imagine H. erectus getting away with this burden
on their resources, unless they had a complex and stable social structure. So we have to imagine them living reasonably
settled lives in, say, village-sized communities.
There may be few complete skeletons. But a lot of skulls have clearly been found,
because the scientists have been able to chart a gradual increase in the size
of their brains, until its average was nearly twice the size of that of H.
habilis. This is the largest spurt
in brain size of any of our ancestors.
Even the one that led directly to us pales in comparison.
It needs some explanation. You can’t just grow your brain willy
nilly. Brains use a lot of energy, and
you have to have this extra energy available before you can develop your brain.
The classical explanation is meat.
The H. erectus
folk may well have started out mainly as scavengers, seeking out the remains
that animal predators had left – or driving the smaller ones off their
prey. If so, their new-found walking and
running abilities made them much better at it.
And it gave them a much richer diet.
As a result, they were able to shrink their guts, and
to reduce the amount of energy expended in digesting their food. So more energy was available for powering
their brains. They became better still
at acquiring meat … which led to a virtuous circle, and to this eventual
doubling of brain size.
I personally have no doubt that it also led to their
becoming serious hunters in their own right, whether or not they started out
that way.
H. erectus
inherited the ancient Oldowan toolkit from their Homo Habilis ancestors. But
at some point they invented a brand new one, the Acheulian toolkit (more).
Acheulian tools are more difficult to make than Oldowan tools, and they
need more strength. But they are much
more effective too. And the kit
contained a wider range of tools. Most
of them appear to be for butchering.
What is most striking about the Acheulian tools is
this. They are normally far better made
than they need to be to do the job.
‘Exquisite’ seems to be the appropriate word for many of them. Many of the tools were discarded completely
unused, presumably because they weren’t exquisite enough. According to Wikipedia, this suggests that
the roots of human art, economy and social organisation all arose as a result
of the development of these tools. I’d
prefer to see it put the other way round.
This craftsmanship ‘for its own sake’ arose as a consequence of all these things.
Even more importantly, these folk had the leisure to indulge in such
frivolities.
I’m slightly puzzled by the apparent absence of
weaponry in the toolkit. Perhaps their
weapon tips were made of bone or fire-hardened wood, neither of which would
preserve well. On the other hand, maybe
a well organised band of hunters doesn’t need high tech weapons to be
effective. In Canada there’s a place called
“Head-bashed-in Buffalo Jump”. It takes
little imagination to work out how the locals acquired their meat!
But where did H.
erectus come from? We have a bit of
a problem here. There don’t appear to
have been any climate changes in Africa to trigger a spurt in evolution just
then. Nor in Africa does H. erectus have any “clearly
identifiable immediate ancestors”.
There is a theory that extinctions are more to do with
the theories of Malthus. Malthus pointed
out that populations have the potential to expand exponentially, although in
practice they are self-limiting. He
believed that starvation, illness, war etc. were the likely causes of this
limitation. This theory leads naturally
to the conclusion that pressure from other hominids was the likely cause of
many of the extinctions. However it’s
not something that you can prove. And so
far I’ve only found one scientist who holds this view.
But a totally new explanation is gaining ground,
courtesy of Professor Richard Wrangham of Harvard. I first saw it in New Scientist (1.7.06), but now Science
(21.0.07) has corroborated it. It neatly
solves the problem of their being no explanation or evidence (without invoking
Malthus anyway) of how H. erectus
arose where he was supposed to.
In essence, he didn’t
In the past decade H.
erectus remains have been found in five non rift-valley sites, that were
very nearly as old if not 
older
than the first evidence from the rift valley areas. It seems that H. erectus appeared almost simultaneously in Africa, East Asia and
somewhere in between.
We discuss the Australopithecines in
Around the right time, 1.8 My ago, there was a pulse
of cooling. But it occurred in
Asia. It didn’t reach Africa. So it was Asia where the selective pressure
for rapid evolution was intense. Dmanisi
in Georgia seems to be the favoured candidate, because the finds have about the
right date (1.75 My). Both a skeleton
and simple Oldowan tools have been found there.
It’s also in the middle of the region over which H. erectus appeared so quickly.
The Science article that we
mentioned earlier describes some bones that have been found at Dmanisi. They’ve been dated to 1.77 My. They are clearly either of very primitive H. erectus, or of folk who are very
nearly there – but not quite. This
picture comes from the Science
article. Incidentally, I don’t think we
should be too worried if the dates don’t seem to tie up perfectly.
Then, as conditions deteriorated further, why would
not some of them have headed south where it was warmer – reaching
Cowen
reports evidence that these guys had fire at least a million years ago. He reckons that the degree of co-operation
needed to control, maintain and transport a fire is very high, which again
implies a proper social structure and organisation.
But
Cowen goes further. He can’t imagine a
camp fire without people wanting to chat.
Over time, the chat will have ranged wider and deeper, and the
‘language’ will have evolved to make it possible to discuss these things. So Cowen believes that the dawn of language
must have been about then. This is far
earlier than most scientists accept. The
received view is that language was ‘invented’ by us, Homo sapiens, some 15 thousand years ago. But of course it all depends on what you mean
by ‘language’. (More
on language.)
Fire and cooking
The Harvard university
primatologist Richard Wrangham also believes H. erectus were into fire – and also cooking. His theory is reported in both Science (15.6.07) and Sci. Am. (Jan.08). If it’s in these two august journals then we
have to take it seriously whatever Wrangham’s critics may say. Besides it fits in with the thesis that I
peddle throughout this site, namely that our ancestors were a good deal smarter
than we – or many scientists – give them credit for.
Wrangham’s argument is quite
different from Cowen’s. He doesn’t
believe that eating raw meat reduces the energy burden on the digestive system
enough to explain H. erectus’s
explosive increase in brain size. He has
established that cooking, both for meat and for vegetables, further reduces the
energy burden. After trying to eat
chimpanzee food, he says “I realised what a ridiculously large difference
cooking would make”. Cooking makes the job of the digestive system very much easier. So it releases more energy for other things like powering the brain.
We have to say that other
scientists reckon that H erectus
could have obtained the necessary extra energy simply by eating their prey’s
soft parts such as bone marrow and brain tissue. And it’s noticeable that carnivore animals go
straight for the soft unmentionable bits of their prey.
But I’ve not seen any
explanation of why our earlier ancestors couldn’t have eaten these soft bits
just as easily as H. erectus. Maybe H.
erectus were the first to have the idea, or maybe it needed the improved
Acheulian toolkit to gain access to them, but I shall continue to have
difficulties with both these explanations until I’ve seen them explained
properly.
Another problem for Wrangham
is that the evidence for fire taming anything like as early as this is very controversial.
If cooking had become an indispensable part of daily life, then many
scientists would have expected a veritable trail of stone hearths surrounding
scorched earth and so on. But such a
trail only appears within the past 250 thousand years at the earliest.
Before that, signs of
controlled fire are extremely few and far between. But they do exist. For example a site has been found in Kenya,
dated to 1.6 million years ago, in which a patch of scorched earth incorporates
a mixture of different wood types – and no signs of roots having been burned
underground. You don’t get this with
natural phenomena such as forest fires.
They both cover a wide area and scorch the roots. Lightning strikes are local like cooking
fires. But they involve only one type of
wood, and also scorch the roots.
In any case, how much does it
matter? After all, scientists regularly
tell each other that “absence of evidence is not evidence of absence”. How long would you expect the evidence of a
fireplace to last if it wasn’t in a protected cave or something?
Personally I’m very taken
with Wrangham’s idea. But you will have
to make up your own mind.
[Click for next chapter, the spear throwers.]
© C B Pease, February 08