idea of that essay was reached. This idea, that the forms of organisms, in respect of the different kinds of their symmetry and asymmetry, are caused by their different relations to surrounding incident forces, implies a general recognition of the doctrine of Evolution, a further extension of the doctrine of adaptation, and a foreshadowing of the theory of life as a correspondence between inner and outer actions.
In 1852 Mr. Spencer published in the Westminster Review the "Theory of Population deduced from the General Law of Animal Fertility," setting forth an important principle which he says that he had entertained as far back as 1847. Here also the general belief in Evolution was tacitly expressed; the theory being that, in proportion as the power of maintaining individual life is small, the power of multiplication is great; that along with increased evolution of the individual there goes decreased power of reproduction; that the one change is the cause of the other; that in man as in all other creatures the advance toward a higher type will be accompanied by a decrease of fertility; and that there will be eventually reached an approximate equilibrium between the rate of mortality and the rate of multiplication. Toward the close of this argument there is a clear recognition of the important fact that excessive multiplication and the consequent struggle for existence cause this advance to a higher type. It is there argued that "only those who do advance under it eventually survive," and that these "must be the select of their generation." That which, as he subsequently stated in the "Principles of Biology," Mr. Spencer failed to recognize at this time (1852) was the effect of these influences in producing the diversities of living forms; that is, he did not then perceive the coõperation of these actions of the struggle for existence and the survival of the fittest with the tendency to variation which organisms exhibit. He saw only the power of these processes to produce a higher form of the same type, and did not recognize how they may give rise to divergencies and consequent differentiations of species, and eventually of genera, orders, and classes.
Early in 1852, Mr. Spencer also printed a brief essay in the Leader, on "The Development Hypothesis," in which some of the now current reasons for believing in the gradual evolution of all organisms, including man, are indicated. To this paper Mr. Darwin refers in the introductory sketch of the previous course of research on the subject of development, which he prefixed to the "Origin of Species." In this essay, however, direct adaptation to the conditions of existence is the only process recognized.
In October of the same year (1852), Mr. Spencer published an essay in the Westminster Review, on the "Philosophy of Style," in which, though the subject appears so remote, there are traceable some of the cardinal ideas now indicated, and others that were afterward developed. The subject was treated from a dynamical point of view, and, as Mr. Lewes remarks in his essays on the "Principles of Success