Infanticide (zoology)
At the time it was first seriously treated by Yukimaru Sugiyama,[6] infanticide was attributed to stress causing factors like overcrowding and captivity, and was considered pathological and maladaptive.
Possible reasons it was not treated as a prevalent natural phenomenon include its abhorrence to people, the popular group and species selectionist notions of the time (the idea that individuals behave for the good of the group or species; compare with gene-centered view of evolution), and the fact that it is very difficult to observe in the field.
Infanticide not only reduces intraspecific competition between the incumbent's offspring and those of other males but also increases the parental investment afforded to their own young, and allows females to become fertile faster.
[10] As males are in a constant struggle to protect their group, those that express infanticidal behavior will contribute a larger portion to future gene pools (see natural selection).
Similar behavior is also seen in male lions, among other species, who also kill young cubs, thereby enabling them to impregnate the females.
Males have, on average, only a two-year window in which to pass on their genes, and lionesses only give birth once every two years, so the selective pressure on them to conform to this behavior is strong.
It is no coincidence here that the female gestation period is three weeks as well, or that it takes roughly two months for pups to become fully weaned and leave their nest.
[13] The adaptive value of this behavior switching is twofold; infanticide removes competitors for when the mouse does have offspring, and allows the female victims to be impregnated earlier than if they continued to care for their young, as mentioned above.
Gerbils, on the other hand, no longer commit infanticide once they have paired with a female, but actively kill and eat other offspring when young.
This is less common than infanticide of existing young, but can still increase fitness in cases where the offspring could not possibly have been fathered by the new mate, i.e. one gestation or fertility period.
It seems rather that males are more successful in avoiding infanticidal females when they are out of the water with their eggs, which might well explain the ultimate cause of this behavior.
[3] The surprising finding of the study was that by far the most common type of infanticide involved the killing of close kin's offspring.
Similar behavior has been reported in the meerkat (Suricata suricatta), including cases of females killing their mother's, sister's, and daughter's offspring.
[26] There is less fitness advantage for a conspecific to carry out infanticide if the interbirth period of the mother will not be decreased and the female will not return to estrous.
Taking a broader view of the black-tailed prairie dog situation, infanticide can be seen as a cost of social living.
[30] Because this form of infanticide reduces the fitness of killed individuals' parents, animals have evolved a range of counter-strategies against this behavior.
[33] In this species males often cooperate with the female in preparing a piece of carrion, which is buried with the eggs and eaten by the larvae when they hatch.
This promiscuous behavior is adaptive, because males will not know whether it is their own offspring they are killing or not, and may be more reluctant or invest less effort in infanticide attempts.
[37] Infanticide, the destruction of offspring characteristic to many species, has posed so great a threat that there have been observable changes of behavior in respective female mothers; more specifically, these changes exist as preventive measures.
A common behavioral mechanism by females to reduce the risk of infanticide of future offspring is through the process of paternity confusion or dilution.
This theory assumes that males use information on past matings to make decisions on committing infanticide, and that females subsequently manipulate that knowledge.
[38] This "pseudo-estrus" theory applies to females within species that do not exhibit obvious clues to each stage of their cycle, such as langurs, rhesus macaques, and gelada baboons.
[35] An additional behavioral strategy to prevent infanticide by males may be aggressive protection of the nest along with female presence.
The small "nuclear families" live in the same permanent shelter and the parents protect their infants from infanticidal conspecifics in this way.
When young bass hatch from the spawn, the father guards the area, circling around them and keeping them together, as well as providing protection from would-be predators.
This was suspected by Rothenbuhler however, who manually removed the caps, and found some hives proceeded to clear out infected cells.
Cornell University ethologist Glenn Hausfater states that "infanticide has not received much study because it's a repulsive subject [...] Many people regard it as reprehensible to even think about it."
Research into infanticide in animals is in part motivated by the desire to understand human behaviors, such as child abuse.
It still takes place in the Western world usually because of the parent's mental illness or violent behavior, in addition to some poor countries as a form of population control — sometimes with tacit societal acceptance.
Infants and young children would often be killed, roasted, and eaten by their mother and sometimes also fed to siblings, usually during times of famine.
