home1.gif (2214 bytes)


Missing Links

Robyn Williams Speaks with Dr Colin Groves

Ockham's Razor ABC Radio National Transcripts Sunday 19 January 1997

Dr Colin Groves received his PhD in 1966.  He has held fixed-term appointments in the University of California and in Cambridge University before migrating to Australia to take up a post in the Australian National Universary., Department of Archaeology and Anthropology (formerly Prehistory and Anthropology) where he is now Reader.


Should scientists be speculating about the missing link or links in human evolution - or should that idea by now be abandoned as being irrelevant.

Robyn Williams:

Is there a link? More to the point, is there a missing link? That dread phrase has indeed been uttered in this very program not long ago.

Which annoyed Colin Groves. Dr Groves is an anthropologist and studies bones at the Australian National University in Canberra. So why is he cross about missing links?

Colin Groves:

In 1864 the great British palaeontologist Hugh Falconer wrote to a relative about a primitive-looking skull from Gibraltar, about which he and a colleague had just presented a paper at a scientific meeting:

If you hear any remarks made, you may say from me, that I do not regard this 'priscan pithecoid man' as the 'missing link', so to speak. It is a case of a very low type of humanity - very low and savage, and of extreme antiquity - but still man, and not a halfway step between man and monkey.

As far as anyone can trace, this is the first time that the phrase 'missing link' appeared in print. Trinkaus and Shipman, in their recent book on Neandertals (of which the Gibraltar skull is one), suggest that the way Falconer used the term, in a letter and putting it in quotation marks, implies that it was already in popular currency, presumably since Darwin's Origin of Species had got people discussing human origins five years earlier. Whatever. It has become part of the English language with a vengeance, and a more misused term I cannot imagine.

Has the Missing Link been found? Obviously not, by definition: it is the 'Missing' Link. Just as open to abuse is that other word in the phrase: 'Link', rather than 'Links', implying that there is only one, and that if it is found all will be well with the theory of human evolution, otherwise we may take leave to doubt it.

Human evolution is much more complicated than all that. Creationists, doggedly determined to be both simplistic and out-of-date, talk about australopithecus, 'Java Man' and 'Peking Man'. The reality is far more complex, and far, far more exciting. There are 'australopithecines', different species of Homo, and all kinds of intermediates and side branches. And controversies. Creationists will have you believe that because 'experts' disagree, the subject is in disarray. On the contrary, it is a sign of a dynamic field of inquiry.

The first controversy concerns the time of separation of the human line from that of other living apes - specifically from the line leading to the chimpanzee, our closest living relative. In the 1960s it was proposed that we had an ancestor called ramapithecus that lived between 10 and 15 million years ago. Ramapithecus consisted of some partial upper and lower jaws from fossil sites in India, Pakistan, Kenya and Turkey. The specialists who promoted this particular ancestor carried on excavating in these same sites in the 1970s, hoping to find more complete specimens, and indeed they did - but the new specimens showed that, actually, ramapithecus was hardly different from a better-known, larger fossil ape called sivapithecus, which is an early version of the orang utan. But that's what science is all about: put forward a hypothesis and test it - even at the risk of proving yourself wrong.

If the evidence that the human line was already separate 15 million years ago had thus evaporated, what really was the separation date? Vince Sarich, basing himself on calculations of the rate of evolution of blood proteins, had insisted as long ago as 1966 that it was only 5 to 8 million years ago; after the ramapithecus fiasco, a more recent date like this began to look much better. In the 1980s and '90s, new methods such as DNA sequencing, gave support to the 5 to 8 million date, or even lowered it further.

Suppose the date when the human and chimpanzee lines diverted was around 5 million years ago. What would a human-line fossil from shortly after the divergence look like - say, about 4.4 million years old?

Well, we now have such a fossil, 'ardipithecus ramidus', from Ethiopia. It was described (in 1994) from jaws, teeth, part of a skull, and some upper limb bones; since then, further material has been discovered but not yet published. Every bone and tooth was intermediate between human and chimpanzee - for example, it had canine teeth smaller than a chimpanzee's but larger than a human's - and, by implication it was already adapted to standing and walking upright.

Then come the fossils we call 'australopithecines'. Known by plentiful material - hundreds of individuals - from sites in South Africa, Tanzania, Kenya, Ethiopia and, quite recently, Chad, there were half a dozen or more distinct species, some more primitive and 'Ardipithecus'-like, some more 'advanced' and human-like, some in between. They range in time from a bit over 4 million to 2.5 million years ago, and the forms that used to be known as 'robust australopithecines', but now usually called the genus Paranthropus, survived to as recently as 1 million years ago. The category 'australopithecine' is no longer a formal taxonomic designation; it merely means a stage in the human line when we know they walked upright, but without the refined human striding gait; when their brains were not, or not slightly, larger than those of chimpanzees; when their canine teeth were already not, or not much, larger than our own.

People sometimes seem to expect that, in an intermediate fossil, every organ system should be intermediate; that canine tooth reduction should be almost there, while brain enlargement had hardly started, comes as a bit of a surprise. In fact, this is a well-known phenomenon, called Mosaic Evolution. Simply put, evolution can be fast or slow, or even nearly static, and this applies to different anatomical parts of the same species as well as to different species.

There are excellent fossils of early 'Homo' dating from about 2 million years ago; they had bigger brains than australophithecines, though of course there are intermediate fossils that have been classified as australopithecines by some, as 'Homo' by others. Fragmentary fossils from Kenya, Malawi and South Africa suggest to some specialists that 'Homo' was already detectable 2.4 million years ago. Certainly, it is about this time that we get the first evidence of modified stone tools in the fossil record. Chimpanzees use stones to crack nuts, and modify sticks and grasses to serve as tools, but only 'Homo' is known, so far, to modify stone.

The earliest fossils of 'Homo' - the small brained 'Homo habilis' and its relatives - gave way to larger-brained ones like 'Homo erectus'. Some time between 2 and 1 million years ago, fossils of the human line begin to turn up outside Africa for the first time: China, Java, Georgia, Israel, Spain. Our forebears were becoming able to cope with an even wider range of environments.

The controversies continue. Was 'Homo erectus' the widespread only species in the human line after 1 million years ago, or should we place African and European fossils of that period in a different species? Did 'Homo sapiens' emerge only in Africa, or simultaneously in different regions of the world? And what of the Neandertal fossils (of which the Gibraltar skull, with which I started, is one): are they our ancestors too? And were they confined to Europe and western Asia between 100,000 and 35,000 years ago, or were they more widespread than that, and can their ancestry be traced much further back?

Notice that up to now I have avoided talking about 'ancestors'. Creationists seem to think that if a particular fossil - 'Java Man', say - can be proven not to have been an ancestor, then that refutes the whole idea of human evolution. I hope you'll see by now that it is completely irrelevant whether a particular fossil is an ancestor or not. That the corpus of fossils start off pretty chimpanzee-like and, progressively, get more and more human-like until they merge into the modern human form, that is 'the fossil evidence for human evolution', if you want to use that phrase.

If you are really anxious to point to a fossil species as an actual ancestor, I suggest 'Homo ergaster'. This was already known by a number of skulls from Kenya dating between 1.6 and 1.8 million years ago, when, in the mid-80s, the startlingly near-complete skeleton of a subadult one was found at Lake Turkana. Some authorities class it as a very early variety of 'Homo erectus', but whereas the well-known 'Homo erectus', from a later period in China and Java, seems rather specialised, 'Homo ergaster' has everything one might have predicted in a fossil of its age: clearly more 'advanced' than any australopithecine of 'Homo habilis', it is primitive enough to have given rise to any or all of the later humans - whether the real 'Homo erectus', the Neandertals, or modern humans.

Yet it is just about impossible, really, to confirm that some fossil or other is ancestral to something else. But it doesn't really matter, does it? In a very real sense, the links are there. They are not 'missing'.

home1.gif (2214 bytes)