SERVICE IN EVOLUTION 191
��THE BOLE OP SEBVICB IN EVOLUTION
Bt Pbofhsbob HBBVBY WOODBUBN SHIMEB
1CAS8ACHU8STT8 XNBTITUTB OF TBCHNOLOGT
SEBVICE is an essential of life upon this earth. Compulsory it surely is in the vast majority of plants and animals^ but it becomes more and more voluntary in the higher types of the invertebrate am'mals and finds finally its highest expression among the vertebrates in man«
When one organism is forced to yield its body for the nourishment of another it renders the grossest form of compulsory service. ¥et all aniTnals and many vegetable forms are dependent upon the death of other organisms for the prolongation of their own life.
"Life evermore is fed by death. In earth and sea and eky; And, that a rose may breathe its breath, Something must die.
"The milk-haired heifer's life must pass That it may fiU your own, As passed the sweet life of the grass She fed upon.
To this compulsory service is due nearly all life upon earth and all opportunity for higher development. So that mere living rolls up the debt each individual owes to myriads of other individuals.
A higher type of compulsory service is seen in those organisms in which the production of young results in the death of the parent. This is the case in most herbs among plants and in many protozoons and insects among animals. Though the organism is compelled to perform this service^ it lives its allotted span and then dies; death is not a tragedy. Compulsory service is also rendered by the individuals of one generation to those of the next in the furnishing of food for the developing embryo; the storage of nutriment around the germ in all higher plants, the pro- vision of yolk for consumption within the shell or other envelope in the higher invertebrates and in all vertebrates, except the mammals, as well as the interuterine nourishment of embryonic mammals.
In the instinct, however, which furnishes food and protection to the growing offspring we have, coupled with an involuntary service, a cer- tain amoimt of the voluntary indicated by variability among individuals of the same species in the amount and kind of labor they expend upon their young. This variability, increasing in the higher types of animals.
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