Those who understand by altruism only the conscious sacrifice of self to others among human beings, will think it strange, or even absurd, to extend its meaning so widely. But the justification for doing this is greater than has thus far appeared. I do not mean merely that in the course of evolution, there has been a progress through infinitesimal gradations from purely physical and unconscious sacrifices of the individual for the welfare of the species, up to sacrifices consciously made. I mean that from first to last the sacrifices are, when reduced to their lowest terms, of the same essential nature: to the last, as at first, there is involved a loss of bodily substance. When a part of the parental body is detached in the shape of gemmule, or egg, or foetus, the material sacrifice is conspicuous: and when the mother yields milk by absorbing which the young one grows, it cannot be questioned that there is also a material sacrifice. But though a material sacrifice is not manifest when the young are benefitted by activities on their behalf; yet, as no effort can be made without an equivalent waste of tissue, and as the bodily loss is proportionate to the expenditure that takes place without reimbursement in food consumed, it follows that efforts made in fostering offspring do really represent a part of the parental substance; which is now given indirectly instead of directly. Self-sacrifice, then, is no less primordial than self-preservation. Being in its simple physical form absolutely necessary for the continuance of life from the beginning; and being extended under its automatic form, as indispensable to maintenance of race in types considerably advanced; and being developed to its semi-conscious and conscious forms, along with the continued and complicated attendance by which the offspring of superior creatures are brought to maturity, altruism has been evolving simultaneously with egoism. As was pointed out in an early chapter, the same superiorities which have enabled the individual to preserve itself better, have enabled it better to preserve the individuals derived from it; and each higher species, using its improved faculties primarily for egoistic benefit, has spread in proportion as it has used them secondarily for altruistic benefit. The imperativeness of altruism as thus understood, is, indeed, no less than the imperativeness of egoism was shown to be in the last chapter. For while, on the one hand, a falling short of normal egoistic acts entails enfeeblement or loss of life, and therefore loss of ability to perform altruistic acts, on the other hand, such defect of altruistic acts as causes death of offspring or inadequate development of them, involves disappearance from future generations of the nature that is not altruistic enough--so decreasing the average egoism. In short, every species is continually purifying itself from the unduly egoistic individuals, while there are being lost to it the unduly altruistic individuals.