Darwin's treatment of human evolution in his most famous work, On the Origin of Species, is limited to twelve portentous words: 'Light will be thrown on the origin of man and his history.' That is the wording in the first edition, which is the edition I always cite unless otherwise stated. By the sixth (and last) edition, Darwin allowed himself to stretch a point, and the sentence became 'Much light will be thrown on the origin of man and his history.' I like to think of his pen, poised over the fifth edition, while the great man judiciously pondered whether to indulge himself in the luxury of 'Much'. Even with it, the sentence is a calculated understatement.
Darwin deliberately deferred his treatment of human evolution to another book, The Descent of Man. Perhaps it is not surprising that the two volumes of that later work devote more space to the topic of its subtitle, Selection in Relation to Sex (investigated largely in birds), than to human evolution. Not surprising because, at the time of Darwin's writing, there were no fossils at all linking us to our closest relatives among the apes. Darwin had only living apes to look at, and he used them well, arguing correctly (and almost alone) that our closest living relatives were all African (gorillas and chimpanzees -bonobos were not recognized as separate from chimpanzees in those days, but they are African too), and therefore predicting that, if ancestral human fossils were ever to be found, Africa was the place to search. Darwin regretted the paucity of fossils, but he maintained a robustly bullish attitude to it. Citing Lyell, his mentor and the great geologist of the time, he pointed out that 'in all the vertebrate classes the discovery of fossil remains has been an extremely slow and fortuitous process' and added, 'Nor should it be forgotten that those regions which are the most likely to afford remains connecting man with some extinct ape-like creature, have not as yet been searched by geologists.' He meant Africa, and the quest was not helped by the fact that his immediate successors largely ignored his advice and searched Asia instead.
It was indeed in Asia that the 'missing links' first began to become less missing. But those first fossils to be discovered were relatively recent, less than a million years old, dating from a time when hominids were pretty close to modern humans and had migrated out of Africa and reached the Far East. They were called 'Java Man' and 'Peking Man' after their discovery sites.* Java Man was discovered by the Dutch anthropologist Eugene Dubois in 1891. He named it Pithecanthropus erectus, signifying his belief that he had realized his life's ambition and found 'the missing link'. Disagreement came from two opposite sources, which rather proved his point: some said his fossil was purely human, others that it was a giant gibbon. Later in his rather embittered and cantankerous life, Dubois resented the suggestion that the more recently discovered Peking fossils were similar to his Java Man. Fiercely possessive about, not to say protective of, his fossil, Dubois believed that only Java Man was the true missing link. To emphasize the distinction from the various Peking Man fossils, he described them as far closer to modern man, and his own Java Man of Trinil as intermediate between man and ape.
Pithecanthropus [Java Man] was not a man, but a gigantic genus allied to the gibbons, however superior to the gibbons on account of its exceedingly large brain volume and distinguished at the same time by its faculty of assuming an erect attitude and gait. It had the double cephalization [ratio of brain size to body size] of the anthropoid apes in general and half that of man . . .
It was the surprising volume of the brain - which is very much too large for an anthropoid ape, and which is small compared with the average, though not smaller than the smallest human brain - that led to the now almost general view that the 'Ape Man' of Trinil, Java was really a primitive Man. Morphologically, however, the calvaria [skullcap] closely resembles that of anthropoid apes, especially the gibbon . . .
It can't have improved Dubois' temper that others took him to be saying that Pithecanthropus was just a giant gibbon, not intermediate between them and humans at all, and he was at pains to reassert his earlier stand: 'I still believe, now more firmly than ever, that the Pithecanthropus of Trinil is the real "missing link".'
Creationists have from time to time used as a political weapon the allegation that Dubois backed off from his claim that Pithecanthropus was an intermediate ape-man. The creationist organization Answers in Genesis has, however, added it to their list of discredited arguments which they now say should not be used. It is to their credit that they maintain such a list at all. As I said, both the Java and Peking specimens of Pithecanthropus have now been shown to be quite young, less than a million years old. They are now classified along with us in the genus Homo, retaining Dubois' specific name erectus: Homo erectus.
Dubois chose the wrong part of the world for his single-minded quest for the 'missing link'. It was natural for a Dutchman to head first for the Dutch East Indies, but a man of his dedication should have followed Darwin's advice and gone on to Africa: for Africa is where our ancestors evolved, as we shall see. So what were these Homo erectus specimens doing out of Africa? The phrase 'out of Africa' has been borrowed from Karen Blixen* to refer to the great exodus of our ancestors from Africa. But there were two exoduses and it is important not to confuse them. Relatively recently, maybe less than 100,000 years ago, roving bands of Homo sapiens looking pretty much like us left Africa and diversified into all the races that we see around the world today: Inuit, native Americans, native Australians, Chinese, and so on. It is to this recent exodus that the phrase 'out of Africa' is normally applied. But there was an earlier exodus from Africa, and these erectus pioneers left fossils in Asia and Europe, including the Java and Peking specimens. The oldest fossil known outside Africa was found in the central Asian country of Georgia and dubbed 'Georgian Man': a diminutive creature whose (rather well-preserved) skull is dated, by modern methods, to about 1.8 million years ago. It has been called Homo georgicus (by some taxonomists, although others don't recognize it as a separate species) to indicate that it seems rather more primitive than the rest of the early refugees from Africa, who are all classified as Homo erectus. Some stone tools slightly older than Georgian Man have just been discovered in Malaysia, sparking a new search for fossil bones in that peninsula. But in any case, all these early Asian fossils are pretty close to modern humans and all are nowadays classified in the genus Homo; for our earlier antecedents we must go to Africa. First, though, let's pause to ask what we should expect of a 'missing link'.
Suppose, for the sake of argument, we take seriously the original confused meaning of the term 'missing link', and seek an intermediate between chimpanzees (see right) and ourselves. We are not descended from chimpanzees, but it is a fair bet that the common ancestor that we share with them was more like a chimp than like us. In particular, it didn't have a huge brain like ours, it probably didn't walk upright as we do, it probably was a lot hairier than we are, and it surely didn't have such advanced human features as language. So, even though we must remain adamant, in the face of common misunderstanding, that we are not descended from chimpanzees, there's still no harm in asking what an intermediate between something like a chimpanzee and us would look like.
Well, hair and language don't fossilize well, but we can get good clues about brain size from the skull, and good clues about gait from the whole skeleton (including the skull, for the foramen magnum, the hole for the spinal cord, points downwards in bipeds, more backwards in quadrupeds). Possible candidates for missing links might have any of the following attributes:
1 Intermediate brain size and intermediate gait: perhaps a sort of stooping shamble rather than the proudly erect bearing favoured by sergeant majors and deportment mistresses.
2 Chimpanzee-sized brain with human upright gait.
3 Large, more human-like brain, walking on all fours like a chimp.
So, bearing these possibilities in mind, let's examine some of the many African fossils that are now available to us, but unfortunately were not available to Darwin.
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