A
TIMELINE FOR THE PLANET click for Home Page
The rise of
humans
How like animals are we?
We are genetically very similar indeed to modern
chimpanzees. It seems that our two DNAs
differ by less than 1½%.
what
is the difference between us and animals? when did our line split off?
So
how come that we’ve been told that animals are just machines? It seems that, back in the 1920s, scientists
made a “hideous philosophical error” (Colin Tudge, New Scientist, 11.3.95).
They decided that animals were just machines, and persuaded the rest of
us to agree. It wasn’t until Jane
Goodall arrived on the scene, around 1960, that this nonsense began to be
questioned.
Perhaps we shouldn’t lay all the blame on the
scientists. Before the coming of steam,
it suited us very well to regard our draught animals as little more than
machines. Even today it suits us to
regard our food animals in a similar light.
One of the capabilities that animals share with us,
I’m sure, is enjoyment. When we see
seagulls wheeling around in the up draughts against the cliffs, how can we
doubt that they are doing it for fun?
There’s no food for them up there.
Of course they are also honing their skills. But that’s why we do things for fun – to hone
our skills. Many of the skills that we
acquire in this way are pretty useless to us now. But the principle must be the same.
[Click for a more complete story, including more about
scientists’ “philosophical error”.]
So what is the difference
between us and animals?
Well for what it’s worth this is my take on it.
I reckon that we are animals, with an extra layer of
computing power added.
Our basic brains are very much the same as that of
animals – at least the higher ones. That
is becoming clearer every day. And it’s
from this basic brain that we get the capabilities that animals have. For the higher animals at least, this
certainly includes a certain amount of thinking, culture, toolmaking, and other
things that we used to regard as uniquely human – including enjoyment!
But then we went on gradually to develop a major
upgrade. We acquired an extra layer of
more sophisticated brain, tacked on top.
This enables us to take these capabilities so much further than any
animal as to be out of sight.
That’s the best I can do.
When did our line split
off?
It depends on who you ask. Let’s say between 5 and 7 million years ago,
possibly somewhere around
The common ancestor of both us and the chimpanzees
seems to have been a primate called Ardipithecus.
The origins of walking
Until
very recently, the debate over walking seemed to concentrate on some
But now it seems that the early ancestors, of all apes,
had long been into “hand assisted bipedalism”.
They walked along the slender outer branches of trees, holding on to
other branches for security, to get at the best fruits. They also used these branches as a bridge to
the next tree.
The ancestors of modern orang-utans, like this guy,
kept the ability. And so did our
ancestors. But those of other apes lost
it.
So when climate change forced our ancestors down from
the trees, we were already reasonably well prepared for it.
However our early ancestors’ walking ability was
hampered by the need also to be good at tree climbing. It was not until the arrival of ‘the mightily
hunter’, Homo
erectus, that we became true people of the plains.
[Click for a more complete story, including the first hard
evidence.]
Our first serious ancestors
The
folk who split off from Ardipithecus,
and ended up with us, are called hominids.
We know very little about the early hominids. The evidence simply isn’t
there. (There’s a fashion to rechristen
us all hominins. The new name seems to mean exactly the same
as the old. I’ve seen no convincing
justification for the change. So I’m
sticking with hominids for now.)
But we do know about the Australopithecines (nothing to do with
Over that that time they developed quite a lot, though they still had “the brains of apes
but the bodies of men”. Their brain size
was in fact very similar to that of the smartest modern chimpanzees, at say 450 cc odd. They were smaller than us, at around 65-110
lb. And they presumably lived in social groups,
like their cousins the chimpanzees.
However a cache of robust skulls has been examined. It suggests that, unlike chimpanzees, male
robusts were on average 17% bigger than females. This implies a social grouping much more like
modern gorillas, in which a dominant male maintains a harem of females – for as
long as he can keep rival males away.
[Click for a more complete story, including a new theory about the
wanderings of the Australopithecines.]
The first stone tools
And by 2½ million years ago these ‘brains of apes’
were making stone tools (more). Perhaps this shouldn’t surprise us too
much. Many of the great apes make simple
twig tools. And they use stones to
hammer with. If you hammer too hard,
the stone breaks. And you find yourself
with a useful sharp edge. Maybe the
surprise is that none of the great apes discovered this.
[For a more complete story, including our ancestors’
main toolkits, click on the link above.]
The first primitive humans
We
have another step change now, to the first primitive humans the Homos – H. habilis. H. habilis counts as a primitive human
because they had brains half as large again (around 600 cc), smaller jaws and
teeth than the Australopithecines. Their skulls are much more like ours
too. These early Homos were small, about
the same size as the Australopithecines.
They had a pretty comprehensive toolkit, the Oldowan
toolkit (for more, click on stone-tools link above), which served them well for
over a million years.
It’s not clear that they were much good as hunters,
though their small teeth and large brains suggest that they had a pretty
nutritious and easy-to-eat diet.
You can make a pretty good living from scavenging, as
many modern animals show. And we can
reasonably expect these guys to have done a better job than scavenging animals
because they were smarter.
The importance of brain size
The bigger your brain is, the smarter you are,
right? As a general rule, sure. But don’t be fooled. We modern have a wide range of different
brain sizes, and scientists are beginning to discover that a large brain
doesn’t necessarily go with high intelligence.
For example, there’s the celebrated French intellectual Anatole France. He was obviously very intelligent. But his brain was only 2/3rds the normal size
– about equal to Homo erectus (who
we’re about to come on to).
And when they try to assess how intelligent our early
ancestors were, the scientists haven’t always had a big enough sample to take
these vagaries into account.
Brain size is certainly hugely important but, as we
keep saying, don’t expect things to be simple in this game.
[Click for a more complete story, including birds and ‘The
Hobbit’.
The arrival of the mighty hunter
The next great step occurred around 2-1½ million years
ago, with the appearance of Homo erectus. Opinions differ about how large his brain
was. This shouldn’t surprise us. We’ve just discussed how variable brain sizes
can be, and the anthropologists have very few H. erectus skulls to measure.
In any case, H. erectus’s
brain seems to have grown considerably during his million-year year reign. I’m going for 750 cc, or about half the size
of ours.
During
the reign of H. erectus, the big cats
and the last of the Australopithecenes
vanished. And man the mighty hunter took
over the whole of East Africa.
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.
They had to shrink their pelvises until they were no
bigger than ours are. And their babies
were born as helpless as ours are, with the brain continuing to grow
considerably after birth, just as ours do.
It’s difficult to imagine them 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.
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.
It’s striking that H.
erectus’s Acheulian tools are far better made than they need to be to do
the job (more). The scientists are quite clear that these
tools must have had ‘symbolic’ purposes of some kind. So these ‘primitive’ folk, with brains not
much more than half the size of ours, had the maturity and the imagination to
appreciate exquisite workmanship. This
doesn’t surprise me. It may not surprise
you. But it will horrify some
scientists. These folk had developed a
lifestyle that gave them both the incentive and the leisure to develop their
skills to the full. It has been
suggested that ‘impressing the girlfriend’ was one of the reasons for making
these superb tools. I like it!
Some
scientists reckon that the dawn of language may have been about then. This is far earlier than most scientists
believe. But we’ll never know for
sure. Of course it all depends on what
you mean by ‘language’. You can have a
pretty primitive ‘method of communication’ and still get a lot of knowledge
across (More on language.)
There’s also a theory that H. erectus was into fire and
cooking. The theory has to do with “how
did these folk power their huge brains?”
It seems that cooking allows you to expend less energy digesting both
your meat and your veg., leaving more for the brain.
There is evidence for fire
this early, but it’s very controversial.
However scientists regularly tell each other that “absence of evidence
is not evidence of absence”. How long
would you expect the evidence of a camp fire to last if it wasn’t in a
protected cave or something?
It’s not clear when H. erectus finally died out. It could have been as recently as 50,000
years ago.
[Click for a more
complete story, including a new theory about where H. erectus came from.]
The spear throwers
From Homo
erectus on, the picture becomes very confusing. I’ve read that they eventually died out
leaving no issue, but I have to say that I find this difficult to believe. Somewhere within the confusion there must be
a link.
The next big development seems to be the spear-makers
of Heidelberg, Homo heidelbergensis,
about ½ million years ago. They left a cache of exquisite throwing spears. A modern javelin maker would be proud to have
made them. Around that time too (I
think) animal shoulder blades start appearing – with spear holes in them.
Shortly afterwards, around 400,000 years ago, come
‘the Butchers of Boxgrove’, who appear to be the same people. Very few human remains have been found, so we
can’t be sure. The Boxgrove site is all
that remains of quite a large area on the south coast of England. These guys were clearly living the life of
Riley. They had plenty of meat, and
time on their hands to make masses of perfectly good hand axes – and then throw
them away unused – just like the Homo
erectus folk a million years before them.
they weren’t quite good enough to impress their girlfriends. If you don’t like that explanation, then feel
free to think of a better one!
But these guys aren’t our ancestors. The cold returned, and they spawned the
Neanderthals (more).
I’ve read that we Homo
sapiens, and the spear folk H.
heidelbergensis, both stem from a small earlier group called Homo antecessor. They don’t appear to have made much of an
impact in Africa, where they must have evolved. Most of the information about them has been
gleaned from a site in Spain.
[Click for a more
complete story, including the Flint Tool factory.
[Click for the next
phase, modern humans.]
© C B Pease, February 08