Homo and the Australopithecines
Contents Updated: Tuesday, August 24, 1999
Homo and the Australopithecines
According to Johanson and White’s hypothesis, Homo and either one or the other of the Australopithecines lived in the same parts of Africa at the same time. Others believe that both A.africanus and A.robustus were contemporaries of early man. Obviously something must have occurred to distinguish such similar species all with the same ancestor and apparently inhabiting the same region at the same time. Had they been, at some stage, physically separated for long enough for speciation to occur? Or could speciation have occurred without such separation? According to some savannah theorists, natural barriers such as the rift valleys, rivers and mountains of East Africa could have isolated groups of apes for long enough for speciation into the Australopithecines and Homo to occur. The distinctions between them were then maintained through habitat and diet. For other savannah experts, these latter would have been sufficient for speciation without physical separation.
In Johanson’s view, A.afarensis, an upright ape, differentiated by diet into two races that speciated ultimately into A.robustus, an upright ape, and H.habilis, the first man.
A.robustus had a massive jaw. Its jaw muscles were so large they required a bony ridge along the top of the skull to anchor them. Their teeth were large and smooth. Microscopic examination shows marks similar to those on the teeth of a chimpanzee whose main food is fruit supplemented by a variety of other items such as eggs, ants, small mammals and lizards, but not roots, the grit of which causes deep scratches. The massive jaws, teeth and jaw muscles suggest a bulky diet of low grade food requiring a lot of chewing—probably fruit and leaves. H.habilis was more omnivorous. Examination of their teeth shows them to be deeply scored like those of a rooting animal. A pig, for example, has scratched teeth from the grit it eats with its diet of roots. Early humans must therefore have taken a lot of grit with their food suggesting roots, meat—probably largely scavenged—and possibly dung. It is humbling to think that we might have set out as eaters of other creatures’ faeces!
H.habilis used a fairly simple tool consisting of a rounded stone knapped on one side to give a sharp edge. The rounded side was held in the hand while the tool was used for scraping and cutting. Nigel Calder describes H.habilis as mutant apemen with overgrown heads and an unprecedented ability to enlarge their brains after birth. A modern human baby has a head only the size of an ape but it grows to three times its birth size during childhood, the greatest enlargements being in the region which has to do with solving problems and language. Nevertheless H.habilis brains were only about half the volume of those of modern humans.
Homo Erectus
Their successors, H.erectus, were hunters not scavengers. They were cleverer and used a hand axe, a stone chipped to a point and held, club-like in the palm. Cutting tools were important to herbivores turned meat eaters. Chimps and baboons, though they might have had the same intellectual potential, did not have the same incentive to make cutting tools as the weak toothed apes. They had no need to invent tools to help them eat meat because their teeth were strong enough. The simplest tools were stone flakes used to cut strips from carcasses.
A microscopic examination of stone chips can be used in the same way as a microscopic examination of teeth. It can reveal what materials they have been used on. An examination of stone chips from 1.5 million years ago shows that some were used for meat cutting, some for grass cutting, showing that gathering had become quite sophisticated, and some for wood whittling suggesting the use of wooden tools like wooden spears.
Between 1.5 and one million years ago, Homo erectus, the first true men, definitely used fire. From Homo habilis until the present day teeth have become smaller by 40 per cent mainly through the use of cooking to tenderize meat and vegetables. The increasing diet of meat might have served to distinguish one of the savannah hominids and provided a stimulus for the development of the tools to process it.
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With all this manual activity, refinements of the hand and corresponding changes in the centers of the brain coordinating the hand led to Neanderthal man, who reached Europe 600,000 years ago, able to make sophisticated stone tools. Despite the brutal looking drawings of him in many books, Neanderthal man was probably of the same species as us although his bone structure was somewhat heavier. 200,000 years ago he painted the first pictures on the walls of caves. Arguably it is art that truly distinguishes mankind. Though several other animals can use tools of a sort, no other creature can make recognizable images. H.sapiens neanderthalensis were also the first humans to bury their dead with tenderness and ritual. Bodies were laid carefully in their graves and decorated with freshly picked flowers.
Homo Sapiens
Then inexorably the human animal continued to evolve into new varieties and about 100,000 years ago Homo sapiens sapiens, anatomically modern man, arrived on the scene. It was to be another 60,000 years before he made a real impact. By 34,000 years ago Neanderthal man was extinct.
The genus Homo began in Africa. But where did the species Homo sapiens begin? One view is that H. sapiens evolved after leaving Africa, perhaps emerging as modern man in several places from the previous humans like H. neanderthalensis. The rival view is that a mutant arose in the African stock and it spread everywhere as modern men. In this view H. neanderthalensis had no effect on modern populations because it did not evolve into them or interbreed with them but was supplanted by them.
The evidence depends upon fossil remains and artefacts. But also the evidence of genetics is that Africa has the oldest population of modern people. The reason is that genetic diversity is greater among Africans than among humans elsewhere. A Scot is closer genetically to a Japanese than two African tribes are to each other. The older population has had a longer time for mutations to disperse among the population. The dispersed populations are much more recent and evolved solely from the few who chose to leave so the diversity is less.
More genetic information comes from analysis of mitochondrial DNA which only comes from the mother, so is not confused by sexual mixing. This shows that all modern humans have a single African mother—an Eve—who lived about 150,000 to 250,000 years ago. This looks fairly certain except that the trees are not unambiguous, so some doubt yet remains. However, even if the genetics are sound, the Eve of around 200,000 years ago was not likely to have been an obviously outstanding—or in any way different—woman.
What the genetic story tells us is that the people who survive today were descended only from her. The reason could be that they belonged to a victorious tribe which eliminated the others, or more likely that this Eve had some subtle advantage which she passed on and gave her descendants an advantage. Perhaps this was intelligence or resistance to some tropical disease. It might have been something which enabled her descendants to speak. Her later descendants were obviously more flexible, more able to adapt and better toolmakers than previous humans.
And so we come to civilization. Jericho was the first town with a population of 2000, some 11,000 years ago. Catal Huyuk, in present day Turkey, was the first city, 9000 years ago, with a population of 5000. Cities introduced the diseases of civilization, diseases of overcrowding and insanitation, of stress and pollution—venereal disease, plague, cancer, heart attacks, psychoses and warfare. The modern world had begun. Mankind, simple hunter gatherers, ate of the fruit of the tree of knowledge, noticed their nakedness and left the Garden of Eden. With their new found knowledge they invented agriculture and had to toil in the earth from dawn till dusk. But they had discovered an economic system that provided for the exponential growth of human population: 10,000 years ago there were less than ten million people in the world; today there are six billion.
This is a long story. It is a remarkable story—remarkably detailed. But is it true? No doubt we can have confidence in the narrative over the last few tens of thousands of years, but what of the previous ten million years? 40 per cent of the skeleton of Lucy was found, an astonishing proportion, for the truth is that everything we know about human evolution depends upon very few remains indeed. Lucy is the only skeleton of a species, likely to be in the line of man, living between 75,000 and 3.5 million years ago, that is anything like complete. The rest of the remains that this construction is based upon are merely fragments—mainly of skulls.
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