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Female Sumatran orangutan with her baby

Parental investment

Rearing young occurs where the eggs or offspring require looking after, and cannot just be abandoned to fend for themselves as with many species. Care investment may be made before or after birth and the different roles may be carried out by one or both parents. So, for instance, birds need to incubate their eggs and the mother and father often share this duty. Parenting can last for days, months or years with varying levels of involvement by each parent. Sometimes, cooperative breeding takes place where other members of the family assist the parents in looking after the young.

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Animals with this behaviour

Mammals

Birds

Ray-finned fishes

Insects

About

Parental investment (PI), in evolutionary biology and evolutionary psychology, is any parental expenditure (time, energy etc.) that benefits one offspring at a cost to parents' ability to invest in other components of fitness (Clutton-Brock 1991: 9; Trivers 1972). Components of fitness (Beatty 1992) include the wellbeing of existing offspring, parents' future reproduction, and inclusive fitness through aid to kin (Hamilton, 1964).

It is held that parental investment starts from the point when the male and female copulate and the egg is fertilized. The minimal obligatory parental investment for a human male is the effort required to copulate. On the other hand, the minimal obligatory parental investment for a human female is copulation, nine months of pregnancy and delivery. In that case the female investment outweighs the male investment. The difference of minimal obligatory investment between males and females suggests that the amount of investment and effort put into mating and parenting will also differ. In theory, a human male could impregnate any reproductive age woman who is fertile, leading to a large number of offspring from the male. In contrast, a human female can typically have only one offspring in nine months, limiting the amount of children she can have. This suggests that males should be more competitive between one another and females will be more ‘choosy’ because of the amount of investment, searching for the male with best fitness and good genes to pass onto her offspring (Trivers 1972).

Parental investment theory accounts for many of the differences between males and females: these were evolved in order to survive and reproduce. The importance can be seen in modern humans. Human males spend more time caring for their offspring than other male mammals (Bjorklund&Shackelford 1999). This higher parental investment is the result of extended childhood of human offspring. Prolonged human childhood is required in order to develop the brain. Optimally, children learn how to survive, as well as learning about the society and its vices and virtues. However, this requires parental investment in the form of parents ‘leading the way’- teaching and protecting children. Abandoned children may be left to die, though in some cases societies have developed various means of caring for them. Males do spend time caring for their children but to a much smaller degree than mothers. This translates into a general observation that females’ parental investment is much greater than that of males, both before and after childbirth.

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