Imagine a case where the children of a bird each have a 50% chance of being born blind.

But the bird always has on average 4 chicks. So on average 2 will be blind and 2 sighted.

(Perhaps this could evolve if the energy needed to create a chick with 100% probability of being sighted is more than the energy needed to create two chicks each with 50% probability of being sighted. The eye being a very complicated organ).

Now, the mother brings food to the chicks and only the sighted children eat the food. The blind chicks (the 'runts') are thrown out of the nest. (It is common there being a 'runt' of the litter. So this scenario has some truth in it.)

Thus all adult birds of this species are sighted. (The 'fittest' birds).

(This is a kind of surival of the fittest but in a family setting.)

Is there a name for this kind of process? This could happen in any animal that has on average more than 2 children. Where it might be cost effective not to make sure that 100% of the children are fit, because the weakest will die anyway.

Secondly, imagine a scenario, where there is a surplus of food one year, so that even the 'runts' make it to adulthood. Now, 50% of the adult birds will be blind. And people might say "There is an epidemic of blind birds". Can we make comparrisons with the theory that there is "an epidemic of myopia" in modern human populations, possibly due to modern medicine decreasing childhood mortality?

  • 3
    $\begingroup$ "Survival of the fittest" is a flawed summary of natural selection that covers up some nuance in the theory (and was not originally used by Darwin but rather a phrase used to try to explain the theory, and then, probably unfortunately, edited into Darwin's own work). Your question seems to lack a basic understanding of heritability and evolution. In particular, your model seems to not involve a heritable trait. $\endgroup$ – Bryan Krause Jul 19 '19 at 22:37
  • 1
    $\begingroup$ Is there a name for this kind of process? You described a non-heritable lethal trait with a prevalence of 0.5 (which is very unlikely). Does this answer your first question? I don't understand what you mean by Where it might be cost effective not to make sure that 100% of the children are fit, because the weakest will die anyway.. Can you please clarify what is on your mind? $\endgroup$ – Remi.b Jul 19 '19 at 23:36
  • 1
    $\begingroup$ Your second question starts with Can we make comparrisons. One can only compare whatever they want to compare. One can even make analogies. But that does not mean there is much to be taken from it. Can you please write a clearly defined question or, otherwise, maybe just remove this second point. $\endgroup$ – Remi.b Jul 19 '19 at 23:38
  • 1
    $\begingroup$ @zooby I understand evolution Take no offense but the phrasing of everything in your post strongly suggests that you don't have much knowledge in evolutionary biology. $\endgroup$ – Remi.b Jul 21 '19 at 2:36
  • 1
    $\begingroup$ @zooby You will probably want to have a look at wikipedia > siblicide. A famous example of siblicide (not listed in the wikipedia article) is the case of shark that kill each other in the mother's womb (see this popular article) $\endgroup$ – Remi.b Jul 21 '19 at 2:41

This competitive relationship often goes by the simple and intuitive name of sibling rivalry, and its closely related idea of parent-offspring conflict. While it may seem counter-intuitive for evolution, you must remember that while it's better for the parents to have multiple surviving chicks, it's better for the chick to have less siblings to compete with for insufficient food.

We do in fact, see this type of behavior amongst humans as well: who amongst us with a sibling has not competed for parental resources and affection? Fatalities, though, are much rarer than in birds that routinely have more chicks than they can support, because our species are different.

| improve this answer | |
  • $\begingroup$ Yes, "sibling rivalry" is probably the right phrase. By question is really, whether there is a name for an animal deliberately making children compete in order to weed out the most fittest or healthiest and discard the runts of the litter. (And also since humans used to have lots of children, whether this sibling rivalry is good for health of a population.) $\endgroup$ – zooby Jul 20 '19 at 20:55
  • $\begingroup$ Also, I make a side point, that if an animal was to stop having lots of children and so there was less sibling rivalry, would this be bad for the health of the species? $\endgroup$ – zooby Jul 20 '19 at 20:58
  • $\begingroup$ @zooby In general, there's no "deliberately" involved, since you're not talking about animals with sufficient cognitive faculties to make such a choice. Even with humans, how often do you think that a parent deliberately makes their children compete, vs. falling into it as a side effect of their own choices and patterns? As for whether it's "good" for the population---it doesn't have to be, it just has to be a stable equilibrium. $\endgroup$ – jakebeal Jul 20 '19 at 23:58
  • $\begingroup$ Well I mean deliberate in the sense of a stable equilibrium, like you say, that has evolved over thousands of years. Perhaps birds evolved under the assumption their chicks compete. Perhaps humans evolved to have their children compete, and stopping the children compete will upset the equilibrium and be bad for the population's health however one might define it. Perhaps it is "natural" for humans to have 10 children who fight to the death leaving only the two fittest to reproduce. $\endgroup$ – zooby Jul 21 '19 at 5:18
  • $\begingroup$ What I'm trying to say is, whether there is reasearch into how much "sibling rivalry" is essential for maintaing the health of a population. Or having enough children incase some of them are weak is important vs having only two children and hoping they are both strong. $\endgroup$ – zooby Jul 21 '19 at 5:25

Not the answer you're looking for? Browse other questions tagged or ask your own question.