Maggie A's Meanderings




 June 11, 2015

Kill Male Babies --
The Case for Male Infanticide

I was reading Odd Couples - Extraordinary Differences between the Sexes in the Animal Kingdom by Daphne J. Fairbairn. Reading the chapter on the Great Bustards (the heaviest flighted bird), I learned that a male Great Bustard is highly unlikely to ever mate. For Great Bustards males, mating is reserved for the very exclusive few. The males must grow a showy plumage, establish dominance, defend a display area, then perform for the females. The females choose who to mate with and they only pick the best. The vast majority of male Great Bustards don't even survive to sexual maturity as male Great Bustards have a higher death rate than the females. Of those males that do survive, they still have a small chance of ever mating due to the choosiness of the females. Whereas any Great Bustard female that makes it to sexual maturity is basically guaranteed to mate.

Male Great Bustard chicks are also expensive to raise. It can take almost a year to raise a Great Bustard chick, and males, being significantly larger than females, take a lot more food. In the Great Bustards, the females raise the chicks with absolutely no help from the males ---- the male's participation in fatherhood ends at copulation. And, unlike ducks or geese, it's not a matter of the mother showing the chicks where the food is and the chicks feeding themselves. In Great Bustards the female has to catch/gather all the food for the chicks when they are young and, even when the chicks are older, the mother continues extra feeding sometimes until the chicks are 9 or 10 months old. Every bit of food that a mother gives to her chicks is less food for her which means that she will be in poorer shape, both to survive and to reproduce, in the next breeding cycle. And, as I said, males take a lot more food than females.

So a male Great Bustard chick is going to take a lot of resources to raise and the vast majority of them will return nothing (genetically speaking) because he'll more than likely never mate. 

The thought occurred to me that if Great Bustards were Chinese or Indian, they'd just kill the male babies.

Kill them or abort them. Either way, they'd choose not to raise males because males aren't as valuable. They're expensive to raise and the norm is that they'll return nothing to their parents.

An argument could be made that it would even be to the parent's advantage to kill that offspring. So a Great Bustard mother who realizes her male chick isn't likely to shape up into a prime male and who kills that chick could then spend less of her time & energy gathering food. She only has to find food for herself; everything she gathers, she gets to eat herself. (Plus, if she eats the chick, she'd get some of her resources back that she'd put into him.) This would get her in better shape and starting the next breeding season in better shape is an advantage. And, hopefully, in that breeding season she'll produce either a female chick or a prime male who will one day mate.

This pattern of males that have little chance to ever pass on their DNA is not uncommon in the animal kingdom. We're certainly familiar with it among mammals. There are the harem species like elephant seals and horses. In order for his genetic line to continue a male lion must not only be strong enough to challenge and win a fight for an existing pride but he must then defend that pride until his offspring have grown-up. If the male lion fails in fighting off another male, the new male will kill all the cubs from the previous male so all his breeding will be for nothing (genetically speaking).

So among birds and mammals there are a number of species where the "value" of most male offspring is zero (the males are "unfit") because those males will not be passing on their genes.
(This is the principle known colloquially as “survival of the fittest,” where fitness denotes an individual’s overall ability to pass copies of his genes on to successive generations.) Yet what you don't have is any species that has a sexual preference to killing its babies ----- except for homo sapians, and that's not a species behavior with us; it's a cultural behavior.

If there were a Darwinian advantage in killing babies of one particular sex, such a behavior would have evolved in some species. And given the scenario of male versus female mating odds, who they'd be killing would be the male babies, especially among the Great Bustards. The mothers would put their effort into raising the female babies who are more likely to pass on the mother's genes. Only the strongest, healthiest male babies would be worth the effort to raise ----- all the other male babies would be abandoned or killed.

Yet --- as far as I know --- this sexual selection of offspring behavior doesn't exist in any other species. It's not a reported behavior in mammalian species, and I've never even heard of this behavior in any vertebrate. Male and female offspring are born. Male and female offspring are raised. Infanticide happens among species. Abandonment happens. Starvation through neglect happens. But it happens to both male and female offspring. I've never heard of any species that selectively targets one sex to be killed. So
there must be a Darwinian advantage in raising both male and female offspring even when there's very little chance for the males to ever "give back" by passing on their genes.

But throughout human history certain select cultures, currently among them are the Chinese and the Indians, have come up with a behavior that they think is better than Darwinian evolution. They think the solution to their resource problem is to sexually select their offspring by killing the female babies. (Now with ultrasounds they don't even have to wait for the female babies to be born; they can simply abort the female fetuses.) Aside from the moral issues of killing those babies, it's an incredibly shortsighted decision. I remember giving a sardonic laugh when I heard about this happening decades ago and said to myself "Yeah, just you wait twenty or thirty years when there aren't enough girls for those boys to marry." And, sure enough, there is a shortage of marriageable females in areas where sexual selection of infants was practiced.  Well, only an idiot wouldn't have seen that coming, but clearly there are people who are dumber than a Great Bustard.

Birdbrain insult, Great Bustard
Original photo of Great Bustard by Takkk (Own work) [CC-BY-SA-3.0 or GFDL], via Wikimedia Commons

For more about where humans fit in with other species' behavior patterns, read "As Dumb as Deer."

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