550 EVENING DISCOURSES. 
advance towards the right-hand side of my chart. The line of advance culminated 
in the human stem in the extreme right. Like Haeckel, I recognised certain definite 
stages in the advance towards the human form—a pronograde stage, still represented 
by old-world monkeys ; an early orthograde stage, still perpetuated by gibbons; a 
later orthograde stage, represented now in the bodies of the great anthropoids ; and 
lastly the final orthograde (or plantigrade) posture represented by man. If we accept 
such a succession of evolutionary stages then we can give a rational explanation of 
man’s structure and posture of body ; we can explain the existence of great anthro- 
poids, small anthropoids and pronograde apes and man’s structural relationship to 
them. We can also explain, so far as we have discovered them, the geological records 
of extinct types of apes and man. In brief, a family tree represents a working 
hypothesis ; it must explain—and be the only possible explanation—of how man, 
anthropoid and monkey, have come to be constituted as we now find them. 
Now I do not claim that my formula explains all the facts. Prof. Wood Jones has 
drawn attention to the persistence of many primitive features in the human body 
which have disappeared from those of anthropoids and of monkeys. On the other 
hand, anthropoids and monkeys have retained to even a greater degree a varied 
assortment of primitive features which have disappeared from man’s body. The 
explanation of these anomalies I would seek for, not by modifying the family tree I 
have shown you, but by a better understanding of the laws of inheritance. Living 
animals are structural mosaics; the descendants of a common ancestor may change— 
or revert—in one set of parts while a cousin form changes in quite another set. The 
gorilla reproduces in its liver the lobulation of monkeys, while the orang has a liver 
unified to an ultrahuman extent. 
During the past four years the final form which should be given to man’s family 
tree has been very actively and profitably debated by our colleagues of the United 
States. I can best bring home to you the chief matters now in dispute by showing 
in quick succession three recently constructed human pedigrees, all of them from 
America. The first represents the conception which Prof. W. K. Gregory, of the 
American Museum of Natural History, has based on thirty years of inquiry.! 
Prof. Gregory has introduced an improved method of charting man’s pedigree ; 
nevertheless, it is but a modification of Haeckel’s original scheme which represents 
man as the most changed, the most highly evolved of all primates. The great 
anthropoid stock is depicted as diverging into three branches at the very beginning 
of miocene times, one branch leading towards man, another towards the African 
anthropoids—the chimpanzee and gorilla—and the third towards the line which 
ended in the orang. The extinct anthropoids of the upper miocene and lower pliocene 
are placed on or near one or other of these three divergent branches. We are 
particularly interested in the place given in Prof. Gregory’s scheme to that extinct 
primate discovered at Taungs by Prof. Dart and named by him Australopithecus. 
Prof. Gregory makes Australopithecus spring from the chimpanzee stock late in the 
miocene, and gives this extinct South African anthropoid the nearest place to man, 
the chimpanzee coming next and the gorilla third in degree of proximity to man. 
On the whole, I consider the place given in this scheme to Australopithecus to be the 
best that can be assigned to it in the light of our present stock of knowledge. The 
idea which underlies Prof. Gregory’s pedigree of man is the same as that which guided 
Haeckel in his first scheme and which influenced me in my attempt. All three of 
us have found that in order to derive man from one of the many early eocene primates 
—the tarisoid family is now accepted as the most likely early eocene progenitor— 
it is necessary to suppose at least five stages in man’s ascent—a tarisoid stage, a small 
monkey stage, a small anthropoid stage, a great anthropoid stage and, finally, an early 
human stage. Neither Prof. Gregory nor i can conceive how an early eocene primate 
could arrive at man’s estate except by passing through this or a similar series of stages. 
Another human pedigree published by Dr. Adolf H. Schultz of Johns Hopkins 
University at the close of last year (Human Biology, September 1930) is well worthy 
of consideration. For over twenty years Dr. Schultz has been investigating the 
development and growth of anthropoids and monkeys, and has thus come into 
possession of a large mass of new data. He has drawn a pedigree of man and ape 
to explain his observations. The central position in his scheme is occupied by the 
African anthropoids; their stem emerges from a generalised small anthropoid. 
1« How near is the relationship of Man to the Chimpanzee-Gorilla stock?’ The 
Quarterly Review of Biology, 1927, vol. ii., p. 549. 
