Australopithecus habilis, Homo habilis
Australopithecus habilis, Homo habilis, Australopithecus rudolfensis, Homo rudolfensis
Australopithecus habilis, Homo habilis
'mainstream' ergaster to deserve a different specific name, say Homo habilis. And now we come to the point of this argument. As we go back further still, at some point we must start to hit individuals sufficiently different from modern Homo sapiens to deserve a different genus name: say Australopithecus. The trouble is, 'sufficiently different from modern Homo sapiens is another matter entirely from 'sufficiently different from the earliest Homo , here designated Homo habilis. Think about the first specimen of Homo habilis to be born. Her parents were Australopithecus. She belonged to a different genus from her parents? That's just dopey! Yes it certainly is. But it is not reality that's at fault, it's our human insistence on shoving everything into a named category. In reality, there was no such creature as the first specimen of Homo habilis. There was no first specimen of any species or any genus or any order or any class or any phylum. Every creature that has ever been born would have been classified - had there been a zoologist around to do the classifying - as belonging to exactly the same species as its parents and its children. Yet, with the hindsight of modernity, and with the benefit - yes, in this one paradoxical sense benefit - of the fact that most of the links are missing, classification into distinct species, genera, families, orders, classes and phyla becomes possible.
I wish we really did have a complete and unbroken trail of fossils, a cinematic record of all evolutionary change as it happened. I wish it, not least because I'd love to see the egg all over the faces of those zoologists and anthropologists who engage in lifelong feuds with each other over whether such and such a fossil belongs to this species or that, this genus or that. Gentlemen - I wonder why it never seems to be ladies - you are arguing about words, not reality. As Darwin himself said, in The Descent of Man, 'In a series of forms graduating insensibly from some apelike creature to man as he now exists, it would be impossible to fix on any definite point where the term "man" ought to be used.'
Let's move on through the fossils, and look at some more recent links among those that are no longer missing, although they were missing in Darwin's time. What intermediates can we find between ourselves and the various creatures like 1470 and Twiggy, who are sometimes called Homo and sometimes called Australopithecus? We've already met some of them, as Java Man and Peking Man, normally classified as Homo erectus. But those two lived in Asia, and there's good evidence that most of our human evolution took place in Africa. Java Man and Peking Man and their kind were emigrants from the mother continent of Africa. Within Africa itself, their equivalents are nowadays usually classified as Homo ergaster, although for many years they were all called Homo erectus - yet another illustration of the fickleness of our naming procedures. The most famous specimen of Homo ergaster, and one of the most complete pre-human fossils ever found, is the Turkana Boy, or Nariokotome Boy, discovered by Kamoya Kimeu, star fossil-finder of Richard Leakey's team of palaeontologists.
The Turkana Boy lived approximately 1.6 million years ago and died at the age of about eleven. There are indications that he would have grown to a height of 6 feet if he had lived to adulthood. His projected adult brain volume would have been about 900 cubic centimetres (cc). This was typical of Homo ergaster/erectus brains, which varied around 1,000 cc. It is significantly smaller than modern human brains, which vary around 1,300 or 1,400 cc, but larger than Homo habilis (around 600 cc) which in turn was larger than Australopithecus (around 400 cc) and chimpanzees (around the same). You'll remember we concluded that our ancestor of three million years ago had the brain of a chimpanzee but walked on its hind legs. From this we might presume that the second half of the story, from 3 million years ago to recent times, would be a tale of increasing brain size. And so, indeed, it proves.
Homo ergaster/erectus, of which we have many fossil specimens, is a very persuasive halfway link, no longer missing, between Homo sapiens today and Homo habilis two million years ago, which is in turn a beautiful link back to Australopithecus three million years ago, which, as we saw, could pretty well be described as an upright-walking chimpanzee. How many links do you need, before you concede that they are no longer 'missing'? And can we also bridge the gap between Homo ergaster and modern Homo sapiens? Yes: we have a rich lode of fossils, covering the last few hundred thousand years, which are intermediate between them. Some have been given species names, like Homo heidelbergensis, Homo rhodesiensis and Homo neanderthalensis. Others (and sometimes the same ones) are called 'archaic' Homo sapiens. But, as I keep repeating, names don't matter. What matters is that the links are no longer missing. Intermediates abound.
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