548 EVENING DISCOURSES. 
census of anatomical characters to see if I could construct a family tree which would 
explain how man had come by his share of them, the gorilla, chimpanzee, orang, 
gibbon and monkeys by their respective allotments. I could find no schematic family 
tree which gave a clear-cut explanation of the distribution of anatomical characters, 
but I determined to be guided by the majority of characters, believing that the 
exceptions I encountered would find an explanation in a fuller knowledge of the laws: 
of inheritance. After collecting data for eleven years I drafted in 1900 the chart: 
which I show you to explain the mass of data I had then collected. Man is what he: 
is because of his brain, but I found then and, what has happened since has convinced’ 
me that my surmise was right, that a study of the evolution of posture of body gives 
the clue, not only to the evolution of man, but to that of all the higher primates. 
There are an infinite number of ways in which animals with grasping hands and feet 
can climb trees. There are, however, only two main ways. Such an animal may 
carry its body prone or horizontal to the branch along which it runs. It is pronograde 
in its arboreal posture ; for such primates my friend—now the Hon. Patrick Duncan— 
proposed the name Pronorachites—‘ prone spines.’ The other posture is quite different 
in all its implications. The animal climbs in an upright or orthograde posture. As 
it runs along a branch the body is held at right angles to the plane of movement. To 
such primates—or anthropoids—the name Orthorachites (upright spines) may be 
given. Orthorachites may he of three kinds: in the act of arboreal progression the 
arms may play a more important part than the legs ; the gibbon and orang exemplify 
the brachiating mode of orthograde progression. Or the arms and legs may play a 
more or less equal part, as in the chimpanzee and as in the gorilla, although in the 
latter, especially in the adult male, the legs may be more active than the arms. There 
is the third possibility—where the legs play a more important part than the arms in 
orthograde life in the trees. It was in this latter way I supposed that an arboreal 
orthograde anthropoid had first diverged in a human-ward direction in specialisation 
of spine, leg and foot. It was on the trees, not on the ground, that man came by 
the initial stages of his posture and carriage. 
I held then—and what has happened in the past thirty years has but confirmed 
my conviction—that a study of the gibbon provides the key to those who wish to 
understand the evolution of the great anthropoids and man. Haeckel was right when 
he gave the gibbon a separate position, placed between the old-world monkeys and 
the great anthropoids, yet well apart from both. The gibbon is a primitive old-world 
monkey whose body at an early date became transformed to serve the needs of the 
orthograde arboreal posture. But [ reject altogether the Lamarckian explanation 
of how the transformation of the gibbon’s body was brought about. It was not 
brought about by one generation of Catarrhine monkeys after another seeking to climb 
in an orthograde manner. Adaptation to posture implies fundamental changes in 
the whole organism, changes in the development of all parts connected with locomotion, 
changes in reflex nerve centres, in development and arrangement of muscles and in 
the shaping and growth of bones and joints. How these evolutionary changes we, 
in our present ignorance of developmental processes, cannot explain, but-in estimating 
relationship of ape to man we must regard these postural modifications of structure 
as of the highest value. 
Thirty years ago, when I was constructing a family tree of man and of the higher 
primates, the oldest fossil evidence we then had of the existence of a small anthropoid 
or gibbon-like anthropoid was in deposits of the upper miocene, and as the great 
anthropoid type was already in existence and was clearly derivable from the small 
anthropoid type, I saw that the origin of the orthograde posture as manifested in 
the gibbon must be ascribed to pre-miocene times, that is, in the upper or later part 
of the Oligocene. In 1910 a discovery was made in the deeper or older Oligocene of 
Kgypt which caused me to extend the antiquity of the orthograde posture. Prof. 
Max Schlosser described from that horizon the teeth and jaws of a very primitive 
and small anthropoid ape—apparently an ancestor of the gibbons which he named 
Propliopithecus. Tts teeth and jaws being so like those of the gibbon, we presume 
that the posture of this early oligocene ape was also orthograde. So I had to modify 
my original scheme by carrying the first stage in the evolution of man’s posture 
backwards a good few million years, for on the Osborn scale 16 million years are 
allotted to the Oligocene period. 
Now every serious sttident of human origin accepts the discovery of Propliopithecus, 
the forerunner of the gibbons, as an event of the highest importance. Vropliopithecus 
provides a fixed basis for our speculations concerning the evolution of the higher — 
| 
: 
