ABSTRACT

The broad occurrence of parental care among animals and its significance in the evolution of reproductive strategies was recognized well over a century ago, as were the related concepts of reproductive effort, parental investment, and parent-offspring conflict. The physiologist William B. Carpenter (1851: 592) appears to be the first biologist to have recognized the concept of reproductive effort, but Herbert Spencer (1852,1867) provided the first lucid discussion of these ideas, cast in evolutionary terms. E. Ray Lankester (1870) also contributed to our understanding of them. Strangely, these pioneering efforts were (and still are) largely ignored. About 100 years later, several biologists, including Gunnar Svardson (1949), David Lack (1947,1954,1968), George C. Williams (1966a, 1966b, 1975), Donald W. Tinkle (1969), and Robert L. Trivers (1972,1974) rediscovered Spencer's rules of reproduction. Although Spencer's language is quaint, the concepts are clearly formulated: Spencer on reproductive effort (1852: 256). "Hence, the maintenance of the individual and the propagation of the race, being respectively aggregative and separative, necessarily vary inversely. Every generative product is a deduction from the parental life; and, as already pointed out, to diminish life is to diminish the ability to preserve life. The portion thrown off [gametes, propagules] is organized matter; vital force has been expended in the organisation of it, and in the assimilation of the component elements; which vital force, had no such portion been made and thrown off, would have been available for the preservation of the parent." (original italics). Spencer again on reproductive effort (1867: 408-9). "The total material monopolized by the individual and withheld from the race, must be, stated

as the quantity united to form its fabric, plus the quantity expended in differentiating its fabric, plus the quantity expended in its self-conserving actions. Similarly, the total material devoted to the race at the expense of the individual, includes that which is directly subtracted from the parent in the shape of egg or foetus, plus that which is directly subtracted in the shape of milk, plus that which is indirectly subtracted in the shape of matter consumed in the exertions of fostering the young. Hence this inverse variation is not expressible in simple terms of aggregation and separation. As we advance to more highly-evolved organisms, the total cost of an individual becomes very much greater than is implied by the amount of tissue composing it. So, too, the total cost of producing each new individual becomes very much greater than that of its mere substance. And it is between these two total costs that the antagonism exists." (original italics). Spencer on parental investment (1867: 395). "There must be taken into account a further element-the amount of aid given by the parent to each germ in the shape of stored-up nutriment, continuous feeding, warmth, protection &c.: on which amount of aid, varying between immensely wide limits, depends the number of new individuals that survive long enough to replace the old, and perform the same reproductive process." Spencer on parental care (1867: 415). "We have to avoid being misled by the assumption that the cost of Genesis is measured by the number of the young produced, instead of being measured, as it is, by the weight of nutrition abstracted to form the young, plus the weight consumed in caring for them." (original italics).