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The first Hominids
The hominids are the folk who split off from a joint
ancestor with the chimpanzees called Ardipithecus
– and ended up with us. We know very
little about the early hominids. The evidence simply isn’t there.
There’s a good reason for this. Up to now we’ve been interested in the major
players on the world stage, the dinosaurs, or the entire gamut of mammals. And we’ve been interested in long time
periods. Patchy though the fossil record
may be (more), there are normally places that yield enough
fossils to give the palaeontologists a reasonable story.
But now we’re concerned with a tiny insignificant
group of primates, who lived in an area that was hopeless for preserving
stuff. There was probably very little
to preserve anyway, except a few skulls and perhaps a few more teeth. The rest will have been eaten by sabretooth
tigers.
However there’s enough evidence to say that our
evolution was pretty normal. Our early
ancestors diversified into other species.
Some persisted for quite a while, and some died out quite quickly. They’ve all gone now of course, except
us. Whether we simply out-competed them,
or whether we actively killed the competition off, we may never know.
Earlier ideas that some mystical force was guiding our
development have gone out of the window.
Our own line, the hominids (more) has up to
a dozen species in it. Or maybe only
half a dozen. The devil is in the
detail, and the palaeo-anthropologists have almost as many theories as they
have skulls to work on. This is why I
don’t intend to waste time going into it too deeply.
Our first serious
ancestors
I’ve got much of my information for this from Richard
Cowen’s ‘History of Life’. According to
him our first serious 
hominid
ancestors were the Australopithecines
(nothing to do with
Over that that time they developed quite a lot. But
Cowen describes them all as having “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.
Perhaps we should mention Australopithecines afarensis.
They are mainly famous for ‘Lucy’, a skeleton of a woman that was far
more complete than had been found before.
She was found in northern
More recently an even more complete skeleton has been
found (Scientific American, Dec. 06),
just 4 km away from where Lucy was found.
This skeleton was of a young girl, probably around 3 years old. She has been called Selam. However she lived a thousand year earlier
than Lucy.
Selam’s bottom half was fairly well adapted to
walking. Note the weasel words
though. We will be coming on to a
descendant that was much better adapted still to ground living. But her top half still retained a number of
adaptations suitable for life in the trees.
This has led to a typical scientific ‘debate’. Were Selam’s folk back among the trees? Were these climbing adaptations not yet
affecting their ground-based lifestyles too much, so that they were taking
their time to fade out? Or would Selam
lose them anyway as she got older. These
kinds of issues are meat and drink to those working in the field, but we can’t
afford to regard them as more than details.
There were two main lines of Australopithecines, the ‘robust’ and the ‘gracile’. Their bodies were similar. I’ve read that the ‘graciles’ evolved into
the ‘robusts’, but the report was around 1994 and it seems to conflict with
more recent material.
But the robusts had huge thick 
skulls,
and would have looked seriously ugly to our eyes, not to say terrifying. They had small front teeth but huge
molars. This picture of the famous
‘black skull’ comes from Cowen. The
theory is that they found themselves in an environment where the only food
available was very coarse. So they had
to develop huge jaws, and massive muscles to work them with. The excrescence on the top was to provide an
anchor point for these huge jaw muscles.
The robusts died out around 1.4 million years ago. This incidentally is quite a long time after
the first Homos appeared (see below). Their lifestyle and food sources clearly
didn’t bring them into conflict.
As an aside, a report in Science (30.11.07) says that the robust males grew to around 17%
larger than the females, and took a lot longer to do it. This is reminiscent of modern gorillas. But it is a dangerous strategy, and only
makes sense if a large dominant male can collect together a harem of faster’
growing females and keep them to himself.
If this report is true, then it’s fairly rare behaviour among our
ancestors. Just how rare however is
still under study.
The graciles had a much better diet, either through
luck or because they were that little bit smarter. Their teeth and jaws were still pretty strong
– but nothing like those of the robusts.
The lower picture is of a reconstruction, and comes from Bruce MacEvoy’s
‘Sculpture gallery’. The graciles were
taller and more lightly built.
Fossil evidence suggests that both types of Australopithecine were preyed upon by
the big cats of the time.
In 1999, Cowen was satisfied that we are descended
from the graciles. But I’ve since read
reports that suggest otherwise – in particular an article in New Scientist (1.7.06).
The standard theory is that the Australopithecines, with their short legs and lack of intellect,
were simply not equipped to wander far.
But the logic of this seems strange.
Animals don’t need intellect to follow their food source wherever it
leads. And the New Scientist article sees no reason why the Australopithecines couldn’t have done the same. It seems that an Australopithecine skeleton has recently been found in Chad, which
is 2500 miles away from their heartlands.
The article implies that it has been dated to 3-3½ million years ago.
This was a time when global cooling was encouraging
grasslands to spread from northern Africa to eastern Asia. This includes what
we now think of as the Sahara desert.
Dental studies suggest that, when it was in season, the robusts ate a
lot of grass. Either that, or they ate
small animals that ate grass. In fact
they probably ate both. How do we know?
It seems that teeth grow in layers like trees do. And different plants are differently fussy
about the rare carbon isotope carbon-13 that they take in. It depends on the precise details of the
‘photosynthesis pathway’ that each plant type uses. Some plant-types avoid carbon-13 like the
plague. Animals that live, even
indirectly, on such plants have very little carbon-13 in their teeth. Other types cope with it better. So a record of what you have been eating is
laid down in the layers of your teeth.
All the above being so, why wouldn’t the (robust) Australopithecines follow the grasslands
wherever they went? Just like the
animals did.
The matter is important because it has a bearing on
where Homo erectus, the mighty hunter, came from – as you can see by clicking ‘next
chapter’ below.
[Click for the development of stone tools.]
[Click for next
chapter, the first primitive humans]
© C B Pease, January 08