Turn we now to a further aspect of the phenomena, separate from, but necessarily associated with, the last. Thus far we have considered only those adjustments of acts to ends which have for their final purpose complete individual life. Now we have to consider those adjustments which have for their final purpose the life of the species. (§5 ¶1)

Self-preservation in each generation has all along depended on the preservation of offspring by preceding generations. And in proportion as evolution of the conduct subserving individual life is high, implying high organization, there must previously have been a highly-evolved conduct subserving nurture of the young. Throughout the ascending grades of the animal kingdom, this second kind of conduct presents stages of advance like those which we have observed in the first. Low down, where structures and functions are little developed, and the power of adjusting acts to ends but slight, there is no conduct, properly so named, furthering salvation of the species. Race-maintaining conduct, like self-maintaining conduct, arises gradually out of that which cannot be called conduct: adjusted actions are preceded by unadjusted ones. Protozoa spontaneously divide and sub-divide, in consequence of physical changes over which they have no control; or, at other times, after a period of quiescence, break up into minute portions which severally grow into new individuals. In neither case can conduct be alleged. Higher up, the process is that of ripening, at intervals, germ-cells and sperm-cells, which, on occasion, are sent forth into the surrounding water and left to their fate: perhaps one in ten thousand surviving to maturity. Here, again, we see only development and dispersion going on apart from parental care. Types above these, as fish which choose fit places in which to deposit their ova, or as the higher crustaceans which carry masses of ova about until they are hatched, exhibit adjustments of acts to ends which we may properly call conduct; though it is of the simplest kind. Where, as among certain fish, the male keeps guard over the eggs, driving away intruders, there is an additional adjustment of acts to ends; and the applicability of the name conduct is more decided. Passing at once to creatures far superior, such as birds which, building nests and sitting on their eggs, feed their broods for considerable periods, and give them aid after they can fly; or such as mammals which, suckling their young for a time continue afterwards to bring them food or protect them while they feed, until they reach ages at which they can provide for themselves; we are shown how this conduct which furthers race-maintenance evolves hand-in-hand with the conduct which furthers self-maintenance. That better organization which makes possible the last, makes possible the first also. Mankind exhibit a great progress of like nature. Compared with brutes, the savage, higher in his self-maintaining conduct, is higher too in his race-maintaining conduct. A larger number of the wants of offspring are provided for; and parental care, enduring longer, extends to the disciplining of offspring in arts and habits which fit them for their conditions of existence. Conduct of this order, equally with conduct of the first order, we see becoming evolved in a still greater degree as we ascend from savage to civilized. The adjustments of acts to ends in the rearing of children become far more elaborate, alike in number of ends met, variety of means used, and efficiency of their adaptations; and the aid and oversight are continued throughout a much greater part of early life. (§5 ¶2)

In tracing up the evolution of conduct, so that we may frame a true conception of conduct in general, we have thus to recognize these two kinds as mutually dependent. Speaking generally, neither can evolve without evolution of the other; and the highest evolutions of the two must be reached simultaneously. (§5 ¶3)