Infanticide and Evolution

[Sicarii]

Hi all. I am unable to find answers to these questions after some online research.. Maybe I am not searching for the right keywords. If you can help, I would appreciate it.

 

Is infanticide in some mammals (e.g. lions) an instrument of natural selection? If so, what evolutionary advantages does it offer?

 

Are there any studies on the subject that you can suggest?

 

Thank you.

[Delta1212]

Specifically in lions, I believe it induces the mother to become fertile again, so male lions will kill the cubs of vanquished rivals in order to replace them with their own.

 

In that respect, infanticidal behavior certainly provides a reproductive advantage.

[Velocity_Boy]

Hi all. I am unable to find answers to these questions after some online research.. Maybe I am not searching for the right keywords. If you can help, I would appreciate it.

 

Is infanticide in some mammals (e.g. lions) an instrument of natural selection? If so, what evolutionary advantages does it offer?

 

Are there any studies on the subject that you can suggest?

 

Thank you.

 

 

Great question!

 

As far as Infanticide by the Males of the species, Delta pretty much nailed it. An online Wiki article (with citations) that I found had this to say on that issue..........

 

"Infanticide caused by sexual conflict has the general theme of the killer (often male) becoming the new sexual partner of the victim's parent, which would otherwise be unavailable. This represents a gain in fitness by the killer, and a loss in fitness by the parents of the offspring killed. This is a type of evolutionary struggle between the two sexes, in which the victim sex may have counter-adaptations that reduce the success of this practice. It may also occur for other reasons, such as the struggle for food between females. In this case individuals may even kill closely related offspring.

Filial infanticide occurs when a parent kills its own offspring. This sometimes involves consumption of the young themselves, which is termed filial cannibalism. The behavior is widespread in fishes, and is seen in terrestrial animals as well. Human infanticide has been recorded in almost every culture. A unique aspect of human infanticide is sex-selective infanticide."

However, I think what you were really interested in--and to me is also the more interesting question--regards what is called "Filial Infanticide" where, not a rival Male, but the very Mother of the offspring will commit the act. And sometimes, in a case known as "Filial Cannabilism." go so far as to consume their young. This latter act is done not uncommonly, and almost exclusively, among species of Fish.

The same online article had THIS to say about filial infanticide..............

"This form of infanticide represents a struggle between the sexes, where one sex exploits the other, much to the latter's disadvantage. It is usually the male who benefits from this behavior, though in cases where males play similar roles to females in parental care the victim and perpetrator may be reversed (see Bateman's principle for discussion of this asymmetry)."

Which, I took to mean that in cases of Filial infanticide the mother is doing it pretty much to please and acquiesce to the preferences of the male. So he can father more offspring, which is ANY living creature's #1 priority.

Lastly, this topic begs us to wonder about human acts of Infanticide. From what I know and have researched, it has been known in most cultures, and by far the most common reason for it is due to "sexual preferences for offspring." Meaning of course that the parents were not happy with the sex of the infant, so decided to cut their "losses" and diffuse resource consumption to the unwanted baby and try again. The second leading cause of human infanticide is for the same reason as we saw above with zoological filial infanticide, in that it is done to acquiesce the male's wishes.

[CharonY]

To clarify, fillial infanticide refers to killing of offspring by their parents, not necessarily the mother. And it is actually not limited or even concentrated in fish.

 

 

"This form of infanticide represents a struggle between the sexes, where one sex exploits the other, much to the latter's disadvantage. It is usually the male who benefits from this behavior, though in cases where males play similar roles to females in parental care the victim and perpetrator may be reversed (see Bateman's principle for discussion of this asymmetry)."

 

That part, on the other hand, does not necessarily refer to filial infanticide as the classic example is the one given by delta, where the unrelated male kills off infants to maximize its offspring.

 

 

 

Which, I took to mean that in cases of Filial infanticide the mother is doing it pretty much to please and acquiesce to the preferences of the male. So he can father more offspring, which is ANY living creature's #1 priority.

 

Actually, the killing of offspring by mothers likely refers to species in which the gender role in terms of parental care are reversed. So that the male has a higher net investment in the offspring than the female. In other words, the infanticide would now be at higher cost for the male than the female. In the context of gender asymmetry it would be a means to maximize ones own fitness at the cost of the partner. It has therefore nothing to do with acquiescing to anything (which, in this context, would not necessarily make a lot of sense to begin with).

 

There are other situations in which mother's are killing offspring, but not their own. This is the case in which child rearing is shared by a group for example. I.e. killing of the children of other mother's would increase the chance of one's own, for example.

 

 

Now specifically regarding filial infanticide, the most common assumption was that of energetics. Hamsters are a prime example, in which offspring are eaten when food is scarce, but also under high levels of stress. However, AFAIK, this view is getting challenged by more refined experiments which point to some more complex mechanisms. For example in some cases parents may overproduce and then cull offspring to reduce their cost of raising the young (although it could be folded under the energetics umbrella).

[Sicarii]

Thank you for your responses.

 

While infanticide provides evolutionary advantage to the killer male (or female), could it not harm evolutionary prospect of entire species if, for example, not enough young offspring survive to reproduce? That example assumes infanticide is common, consistent occurrence, which I do not think is factual.

 

Lastly, this topic begs us to wonder about human acts of Infanticide. From what I know and have researched, it has been known in most cultures, and by far the most common reason for it is due to "sexual preferences for offspring." Meaning of course that the parents were not happy with the sex of the infant, so decided to cut their "losses" and diffuse resource consumption to the unwanted baby and try again. The second leading cause of human infanticide is for the same reason as we saw above with zoological filial infanticide, in that it is done to acquiesce the male's wishes.

 

It's a huge problem in India (highly patriarchal society with caste system) and China (exacerbated by one-child policy), but those seem to be economic and legal issues, respectively, as opposed to survival.

[CharonY]

Thank you for your responses.

 

While infanticide provides evolutionary advantage to the killer male (or female), could it not harm evolutionary prospect of entire species if, for example, not enough young offspring survive to reproduce? That example assumes infanticide is common, consistent occurrence, which I do not think is factual.

 

 

Well, evolution is not concerned with potential outcomes and if a strategy provides some fitness advantage over another, it will be favored until the situation changes where it is not the case. I.e. if infanticide is too rampant and one groups stops doing it then it will be reduced (or the species dies out). But there are also specific counter-strategies. For example, I believe in mongoose children are reared in common groups. Often, the dominant female would kill children off, to improve their own survival. But apparently they are unable to distinguish their kids from others, which means they kill them based on timing (i.e. kill kids before they have their own). As a counter-strategy, it was found that the other females would synchronize their fertility cycle with the dominant female, so that they would have offspring at the same time. Also note that the case for infanticide are not necessarily that all are killed off.

In some species offspring are overproduced and culling merely reduces it to a more manageable amount, which may be more successful than trying to rear all.

 

Also, I wonder what precisely do you mean with common and regular? It is not precisely uncommon if you look at various species and it can be tied to sexual reproduction or resource monopolization, but on the other hand it is not that most species spend an inordinate amount in culling other's offspring (with filial infanticide being a rather rare and specialized event).

[Argent]

@CharonY. Are you aware of any studies that examine the practice of abortion in humans arising as a consequence of the same evolutionary pressures that generate it in other species?

[CharonY]

No and it would not make sense. You cannot draw a direct line from evolution to social practices. Also infanticide refers to postnatal killing.

[delboy]

While infanticide provides evolutionary advantage to the killer male (or female), could it not harm evolutionary prospect of entire species

 

 

That's perfectly possible. Evolution (natural selection) only happens at the level of the individual (or even the gene it can be argued). Individuals will do what they can to pass on their genes, even if this is to the detriment of the species as a whole. Many many species have become extinct because of such reasons.

 

I think some believe evolution can happen at species level but I don't think there's any convincing evidence.