Of Miocene and Pliocene great anthropoids at least i 1 distinct species, representing several genera, are known by the discovery of fossil remains—all of them, unfortunately, being of a frag mentary nature. The type of anthropoid prevalent in Miocene times is best represented by the genus Dryopithecus—anthropoids representing the chimpanzee in point of size and posture and showing in their teeth and jaws characters which indicate that the ancestries of the gorilla, chimpanzee and man may have descended or ascended from a Dryopithecque form. So great and intimate are the resemblances between the teeth of primitive man and those of Dryopithecus that Dr. W. K. Gregory is convinced that it was this anthropoidal type which gave evolutionary birth to the human phylum. Great anthropoids of many kinds abounded in the Miocene jungles of northern India as we know from discoveries made by Dr. Guy Pilgrim (Records of the Geological Survey of India, 1915, vol. xlv., p. i ; Memoirs of the Geological Survey of India, 1927, vol. xiv., p. 1). One of these, Sivapithecus, known by fragments of jaws and teeth found in Siwalik deposits, is regarded as a possible ancestor of man by Dr. Pilgrim, but a definite decision cannot be made until more material is available for study.
So far no fossil trace of an anthropoidal type has been discov ered in America ; man had reached his Neanthropic stage of evolution before he entered the New World. In 1922 a much eroded tooth was found in beds of Pliocene date at Snake Creek quarry, Nebraska, which was attributed to an anthropoid ape Hesperopithecus, was the name proposed for it—but later dis coveries have shown that a mistake had been made and that the tooth belonged to a being of another order.
Early in 1925 Prof. Raymond Dart announced the discovery of the fossil skull of a young anthropoid ape, found in a limestone quarry at Taungs, on the eastern border of the Bechuanaland Protectorate and near the Transvaal frontier (Nature, 1925, vol. cxv., p. 195). The geological evidence goes to prove that this anthropoid which Prof. Dart named Australopithecus, cannot be older than the beginning of the Pleistocene—a date at which primitive types of humanity were already in existence. In size of brain, in shape of head, conformation of jaw and tooth, this very interesting and extinct form of anthropoid shows close relation ships to the two surviving African anthropoids—the gorilla and chimpanzee—and, as Prof. Dart has rightly maintained, possessed
certain features which may be called human.
Summary.—Thus, taking all lines of evidence into considera tion, anatomical, biological, embryological and geological, we are led to the conclusion that man has been evolved from a lower form, and that human races, as we know them to-day, are the products of evolutionary processes. There remain great blanks in the line of evidence which links the origin of modern man to an extinct form of anthropoid ape. Between the highest kind of anthropoid and the lowest type of man, represented at present by Pithecanthropus, there still exists a great gap ; the transitional forms which fill this gap still remain to be discovered. Yet the evidence as it stands, imperfect as it is, points to man's departure from an anthropoid status early in the Miocene period, certainly I,000,000 years ago, perhaps more ; that in the Miocene and Plio cene periods his body and limbs became adapted to a plantigrade posture; that his brain underwent expansion in the Pliocene, and particularly in the earlier part of the Pleistocene period, and that as the brain reached a full human status the coarser outward ap pearances of the ape were shed. Of the vitalprocesses whichbrought about these changes we are as yet ignorant, but it is manifest that in his evolutionary. progress man has tended to acquire and pre serve in adult years states which appear at first as transient conditions in foetal or infantile stages. (Prof. L. Bolk, Proc. Acad. of Science, Amsterdam, 1927, vol. xxx., No. 2.) It is becoming clear that the machinery of evolution is that which regulates development and growth, and in these matters knowledge is growing. Experimental embryologists have proved that one group of developing cells can and does regulate the growth and behaviour of a neighbouring group. The theory of hormones has thrown a flood of light on the machinery of evolution (Prof. Chas. R. Stockard, Publications of Cornell University Medical College, 1924, vol. io; Keith, Supplement to Nature, Aug. 18, 1923). It has been proved that substances or hormones are carried by the circulation throughout the living body from a series of glands which include those of reproduction, the adrenal, the thy roid, the pituitary and pineal, and that the substances thus liberated in the body do control its vital reactions and its struc tural form.