We must remember that reproduction appears in the history of life before sex appears. The lower forms of animal and plant life often reproduce themselves without the aid of sex, and it has even been argued that reproduction and sex are directly antagonistic, that active propagation is always checked when sexual differentiation is established. "The impression one gains of sexuality," remarks Professor Coulter, foremost of American botanists, "is that it represents reproduction under peculiar difficulties."[1] Bacteria among primitive plants and protozoa among primitive animals are patterns of rapid and prolific reproduction, though sex begins to appear in a rudimentary form in very lowly forms of life, even among the protozoa, and is at first compatible with a high degree of reproduction. A single infusorian becomes in a week the ancestor of millions, that is to say, of far more individuals than could proceed under the most favourable conditions from a pair of elephants in five centuries, while Huxley calculated that the progeny of a single parthenogenetic aphis, under favouring circumstances, would in a few months outweigh the whole population of China.[2] That proviso--"under favouring conditions"--is of great importance, for it reveals the weak point in this early method of Nature's for conducting evolution by enormously rapid multiplication. Creatures so easily produced could be, and were, easily destroyed; no time had been spent on imparting to them the qualities that would enable them to lead, what we should call in our own case, long and useful lives. Yet the method of rapid multiplication was not readily or speedily abandoned by Nature. Still speaking in our human way, we may say that she tried to give it every chance. Among insects that have advanced so far as the white ants, we find that the queen lays eggs at an enormous rate during the whole of her active life, according to some estimates at the rate of 80,000 a day. Even in the more primitive members of the great vertebrate group, to which we ourselves belong, reproduction is sometimes still on almost as vast a scale as among lower organisms. Thus, among herrings, nearly 70,000 eggs have been found in a single female; but the herring, nevertheless, does not tend to increase in the seas, for it is everywhere preyed upon by whales and seals and sharks and birds, and, not least, by man. Thus early we see the connection between a high death-rate and a high birth-rate.