THE LINEAGE OF MAN
is meagre it tends to show that the various groups appeared in the following succession: (1) tree shrews, (2) lemuroids and tarsioids, (3) monkeys, (4) pro-anthropoids, (5) diversified anthropoids, (6) primitive man, (7) modernized man. But this is also precisely what one would predict from a comprehensive comparative study of the surviving families of Primates, with special reference to the structure of their brains, skull, teeth, hands and feet, and other parts of the body. The main branches of the order are all represented to-day by surviving members. By making comparisons first within each group and then between groups, including both the fossil and the recent forms, it has been possible to decipher the main record of evolution of the brain, teeth, and various parts of the skeleton.
Taking the series as a whole, it shows a remarkable gradation of forms and structures, culminating in various side branches and also in man. It will remain for future palaeontologists to correct errors and to amplify the details of the process of evolution, but the general sequence of events has been worked out independently by a number of investigators, whose results yield a remarkably concordant, consistent story. Thus Keith has shown that when we pass from the monkeys to the gibbons, which stand near the base of the anthropoid-man radiation, we find that the gibbon has already effected profound readjustments of the viscera and skeleton to its habit of sitting upright and of brachiating, or extending the arms upward and leaping from branch to branch. Keith finds that on the whole the gibbon is nearer to man in this internal readjustment to the upright position than it is to the lower primates. Elliott Smith and his students in England and Tilney in America have worked out the sequence in brain structure from tree-shrew to lemur to monkey, gibbon, orang, chimpanzee, gorilla, man, and they find progressive
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