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MAN’S FAMILY TREE. 549 
orthograde primates. Authorities such as Prof. Fairfield Osborn and Prof. Wood 
Jones, who exclude altogether the anthropoid type from the ancestry of man, are 
prepared to accept Propliopithecus as ancestor from which both the chimpanzee and 
man may have arisen. They carry the separation of the human from the anthropoid 
stock back to early Oligocene times, giving man, on the scale of reckoning I have 
adopted for this discourse, an antiquity of some 35 million of years. 
The census which I made of anatomical characters showed me that man and the 
three living great anthropoids—the gorilla, chimpanzee and orang—besides agreeing 
in great bulk of body, shared so many anatomical features of a kind peculiar to them- 
selves that I had to postulate a common ancestor for the big-bodied or giant group. 
It seemed to me then, and it still seems so to me, most improbable that man and the 
great anthropoids and man came independently by such a complex of characters. 
Increase in size of body, which in many orders of mammals has no deep significance, 
was, so far as concerned the higher primates, symptomatic of an extensive series of 
structural changes, one of which was an increase in size and complexity of brain. The 
great anthropoids had bodies which were eight times, or even twenty times, heavier 
than those of the small anthropoid. Great increase of weight entails changes in the 
manner of arboreal locomotion as well as changes in structure of body. In my scheme 
of 1900 I represented the great orthograde primates as being evolved from the small- 
bodied at the very beginning of the miocene period. The discoveries which Dr. 
Fourtan made in the lower miocene deposits of Egypt (1920) supported my inference. 
In deposits from this horizon he found jaws and teeth of two orthograde primates ; 
one was of the size of a gibbon, the other had reached a size which must have been 
about half-way between that ot the gibbon and of man, I therefore suppose that 
the great-bodied pre-troglodytes which afterwards diverged into anthropoid and 
human types came into existence in earliest miocene times. 
This great increase of size of body which we infer affected the anthropoid stem in 
early miocene times was of critical importance. It indicated that a branch of the 
higher primates had entered a period of evolutionary plasticity and was undergoing 
profound functional and structural changes. It was in this plastic period that I 
suppose the human line to have separated from that of the great anthropoids. I 
cannot suppose that a change in a humanward direction could have taken place 
before miocene times. If we attempt to carry man’s separation to an earlier date 
then we cannot account for man’s structural resemblances to the great anthropoids 
unless we suppose that such resemblances to have been independent acquisitions. 
Dr. W. K. Gregory, in making a family tree of man and ape, constructed quite 
independently of mine and based on an altogether different mass of data, also brings 
the human stem from the anthropoid at the beginning of the miocene—practically 
the same date of emergence as I have given. On the Osborn scale of reckoning he and 
I give the human stem an antiquity of about 20 million years. 
How long did it take this early miocene leg-using anthropoid to undergo these 
transmutations which entitled it to be reckoned no longer anthropoid but human ? 
In 1900 there was only one fossil form which gave assistance in solving this problem, 
namely, the man of Java, Pithecanthropus. So far as concerns his lower limbs 
and manner of progression, Pithecanthropus was entirely human. The human posture 
was completely evolved before the end of the pliocene period. We thus allow two 
geological periods, the miocene and pliocene, covering a period of 18 million years, 
for the evolution of the human characteristics of foot, leg, thigh and pelvis. Besides 
the skull of Pithecanthropus we now know those of two other forms of early pleistocene 
man, EKoanthropus (Piltdown man) and Sinanthropus (Peking man). By the end of 
the pliocene period, therefore, the human stem had been in existence long enough 
to have broken up into many divergent branches, but at present we are still uncertain 
whether or not they represent the ancestors of any race now living. Hence in drafting 
our family tree we trace the modern races of mankind to an early pleistocene ancestor 
not yet discovered. If, however, man’s lower extremities and posture and progression 
were fully evolved by the end of the pliocene period, it was otherwise with his brain. 
When we compare the brain casts of those early pleistocene representatives of man 
with their successors in the latter third of the pleistocene period, we see that in this 
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; apparently short period the human brain must have undergone a great increase of 
size, complexity and inferentially, in power. The pleistocene period, to which the 
Osborn scale allows a million years,saw a marked increase of man’s brain power. In 
making my original draft of man’s family tree I adopted, quite unconsciously, 
_ Haeckel’s method of indicating evolutionary progress by carrying the main line of 
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