Parental care is driven, to a surprising extent, by conflict. Conflict occurs between parents and offspring over how much resource is allocated to the offspring. Conflict occurs between parents over which parent delivers the care. And, conflict occurs among sibs over how resources are divided. Ultimately, sometimes this conflict is resolved in cruel ways, with the killing of a juvenile.

How much parental care?

The minimum amount of parental care is none, beyond the nutritional investment in the egg. Investment beyond the minimum comes in the forms of guarding the eggs and young, providing further nutrition, and the social transmission of information.

The fundamental balance, which can be modeled as a game, if whether more reproduction will be gained through producing more offspring or through caring for the offspring which are already present. For most animals, though, this game is very much biassed by evolutionary history; species which produce highly dependent offspring do not exercise a range of potentially successful choices that includes abandonment of neonates.

Even if evolution has already resolved many of the issues, continued conflict over the balance between present and future reproduction is well known in birds and mammals. These conflicts center on issues like the timing of weaning, the timing of dispersal of juveniles, and the balance between the benefits of social foraging and the costs of feeding a larger social group.

Trivers, R. L. 1974. Parent-offspring conflict. Amer. Zool. 14:249-264.

Which parent cares for the young?

In general, if there is substantial parental care the female is the caregiver. Male mates may remain with the female to ensure paternity, particularly if other opportunities to mate are not present, and the male presence sometimes extends to helping with defending the young and collecting food. Most biologists view this assymetry of involvement in parental as an extension off the differences in gametic investment.

In many terrestrial and some aquatic animals the female carries the developing zygote internally prior to laying an egg or giving birth. This gives the male ample opportunity to leave the female, perhaps to search for other mates. In a sense, the female is "stuck" with parental care after laying the eggs or giving birth, because her mate has abandoned her.

In exceptional cases, such as seahorses and midwife toads, males are the primary caregivers. These are interesting examples of how evolution can be driven to unusual solutions.

Clutton-Brock, T. H. 1991. The evolution of parental care. Princeton: Princeton University Press.

Ridley, M. 1978. Paternal care. Anim. Behav. 26:904-932.

Nurturing and helping

The extent to which young animals are unable to care for themselves, and consequently require adult attention, varies dramatically among species. These examples illustrate this range of variation:

The ugly side of animal behavior: infanticide and siblicide

In some cases parent-offspring or sib-sib conflicts over resources are resolved by the death of juveniles. The best studied examples are:

  • egrets
  • prairie dogs

In other cases, males ensure their paternity by killing a female's litter and then mating with her to produce a new litter. An extreme example of this occurs in mice, in which a female aborts her litter if the male in her territory is replaced.

Mock DW, Parker GA 1998 Siblicide, family conflict and the evolutionary limits of selfishness ANIMAL BEHAVIOUR 56: 1-10

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copyright ©2001 Michael D. Breed, all rights reserved