. . .Perhaps only a single species took to the trees; for it is quite possible for a single form, in a new and advantageous habitat, to vary in time into a great number of species.

Of all this we can know nothing: but of one thing we may feel assured, which is that the plantigrade foot is the only one that could have developed into a grasping organ; such a development being impossible to the digitigrade or the hoofed animals. One can readily see how the habit of walking on the sole might tend to a spreading of the toes, in order to obtain a wider and firmer footing. And it is equally easy to see how a free and wide motion in the great toe would aid in this result. The animal may have been at first light in weight and able to support itself on its unchanged foot, but as it increased in size and weight it would need a firmer grasp, and the final result of spread[45]ing its toes for this purpose may well have been the opposable great toe.

It must be borne in min. . . Read More