The problem of synthesis in biology may have reference to the evolutionary origin of living organisms in past time, a process not directly observable but conceivably reconstructible in broad outline: thus to the biochemist this evolution may appear as the evolution of the special biological compounds, to the psychologist as the evolution of “mind”—or at least of types of behavior. Or the problem may refer to the synthesis of the individual animal or plant, a process of construction which typically starts from a detached portion of a parent organism, such as an egg or seed; this is the problem of individual development or ontogeny and is not essentially different from the general problem of growth. But it is clear that the processes of phyletic evolution and of ontogeny must be considered together, since evolutionary history is in reality the history of a succession of individual organisms, each developing from its germ, i.e. of ontogenies; and the ontogenetic process, so faithfully repeated in each individual as it comes into existence, is itself a product of evolution, having originated (apparently by slow and tentative efforts) in the remote past. The succession of individuals has undergone progressive diversification, culminating in the present condition. We may describe our problem, then, as the problem of the factors underlying the synthesis of a highly special process, that by which the diffusely distributed nonliving materials and energies of nature are brought together in a special kind of unification and transformed into a living organism.