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By Root 279 0

the beetles' bright colors indicate the presence of toxins in the body, and a noxious taste to go with them. Your average bird learns to avoid ladybirds, but the beetles themselves are not affected by the chemicals, and so a ladybird is its own worst enemy. Eating just a single egg, whether trophic or not, significantly boosts the growth rate of a ladybird larva, putting a premium on hatching early. In a study of European ladybird beetles, less than half of noncannibals made it to adulthood, but more than 80 percent of the larvae that had eaten a sibling matured successfully.

Earlier laid means earlier out of the egg, with a chance to prey on one's less precocious siblings. But the day that an egg hatches relative to its nest mates is largely under the control of the mother, since she, after all, is the one that puts them all there. This fact brings up an even more sinister aspect of siblicide: frequently the parent encourages it, or at least does nothing to keep it from happening.

Why should parents tolerate such shocking behavior? Once again, think of the offspring not as individuals in their own right, but as units that pass on the parents' genes. If a mother lays many eggs, and they all hatch, but then there isn't enough food for them all, they all starve, and she has lost, big time. If she lays only a few, and it turns out that there would have been enough food for more, she has still lost, albeit not as much. But if she goes ahead and overproduces, and then lets sibling rivalry take its course, she can achieve the golden mean, since exactly as many offspring as the available resources can support will have survived. So a mother that lays her eggs over several days, creating a situation in which they hatch at different times, may be hedging her bets; if food is abundant, everyone gets enough after hatching and all is well. But if not, the earlier-hatching individuals can eat their siblings and ensure that at least some of the offspring make it to adulthood.

Even if they do not actually consume their brothers and sisters, competing for limited food supplied by a parent, and shoving a less insistent sibling away, can achieve the same effect: more food for the one that shouts the loudest. Encouraging the competition, or at least turning a blind eye to it, will benefit the parent more than trying to break up the squabbles and ensure that food is divided equally among the members of the brood. Actual siblicide, rather than garden-variety making one's brothers' and sisters' lives miserable, is expected only under extreme circumstances, since of course the siblings have half their genes in common, and so eliminating them entirely has its costs as well.

Here too is where the parental and offspring interests diverge. No offspring is expected to willingly sacrifice itself, and indeed each one should attempt to get more food and attention for itself than its siblings. This greed is even expected to extend to the hypothetical future siblings the parent could produce; from an offspring's perspective, getting as much as it can right now will benefit it more than allowing its parent to keep some energy in reserve to invest in future offspring. But the parent should only give as much as necessary for the offspring to become independent and able to fend for itself, because the parent will be served best by saving some resources to produce offspring later. The resulting conflict, according to Trivers, leads to weaning tantrums in mammals and many other kinds of behavior in which young animals compete fiercely with their siblings and try to get more than their parent is willing to offer. Social insects, because they share different proportions of their genes with their siblings than their parents or offspring, are particularly prone to these kinds of disagreements.

If all of this sounds uneasily familiar from your own life, or perhaps the lives of some of your friends, you are not alone. One of the foremost theorists in the field of parent-offspring conflict, H. Charles J. Godfray, notes, "There are clear dangers in overinterpreting