The Science Of Sibling Rivalry

Peter Toohey mulls it over:

[Animal behaviorist Scott] Forbes describes how herpetologists, ornithologists, and mammalogists found that “infanticide – including siblicide – was a routine feature of family life in many species,” most commonly seen in birds. Some birds lay two eggs “to insure against failure of the first egg to hatch. If both hatch, the second chick is redundant to the parents, and a potentially lethal competitor to the first-hatched progeny.” The healthy older chick often kills the younger to eliminate the competition, and some parents actually encourage siblicide when the death of the nest-mate doesn’t naturally occur.

After all, if resources are scarce, it’s better that the strongest offspring survive and that their potential efforts go to ensuring that happens. (It’s the old story of genetic replication again: Surviving offspring are more likely to have the strongest genes, and they are the ones that have the best chance of reproducing later and passing those genes on.) Forbes thinks that such extreme jealous reactions are not common in the human species, but “the more modest forms of sibling rivalry that are ubiquitous in species with extensive parental care – the scrambles for food and begging competitions – resemble more closely the dynamics that occur in human families.”