Siblings of diploid-style creatures are roughly 50% genetically related, just like either parent is to a child. In a lot of species, parents (especially mommies, because (one assumes) maternity is never in doubt) take hella care of their children. Siblings, afaict, don’t. In fact, siblings often compete for parental resources.
Why does a 50% genetic relation encourage caretaking in parents, but not so much in siblings?
At the deep biological level it goes like this. Genes are selfish. Monumentally and simple-“mindedly” so. With the result that:
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Parents want their genes to continue. Caring for all kids until any one proves obviously defective is the way to maximize that chance. Once any one is obviously defective, simply abandon it.
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Offspring want their genes to continue. Maximizing the care they get from parents, up to and including killing their sibling(s) to increase that care maximizes their gene’s chance. The only chance that matters to them.
Thanks for the reminder to revisit Dawkins, and I feel you, but still: as ol’ Rick tells us, it’s the genes that are competing, not the organisms. The genes don’t know (“know”) whether they’re in a parent or a sibling. By trying to best (the genes in) sibling A, (the genes in) sibling B could very well be trying to do itself (themselves) in.
If the payoff for parental investment is constant, then I’m going to want them to spend them on me. 100% gene promotion is better than 50%.
But it’s not quite a flat benefit curve. If it’s me getting some luxury vs. my sibling not staving to death, then I (my genes) should want those resources to go to the sibling. Even with 50% payoff, that’s worth it.
I’d guess that siblings are more competitive when resources are tight. I.e., who gets to eat? If there’s only enough for one child, then killing your sibling makes sense. Not so much if the basic necessities are easily met for everyone.
There have been several studies on sibling competition. The primary underlying reason is to differentiate themselves from their siblings for attention from their parents. Even if that attention is negative.
Both siblings and parents want to pass on their genes, but face different challenges:
Parents can invest in their offspring, or abandon them. But if they abandon their offspring, they then have to produce new offspring and they are back to square one. So parents are generally better off helping their offspring until the benefit of helping is less than the loss of opportunity to produce new offspring.
Siblings can either focus on their own reproduction, or help their siblings reproduce. Depending on the circumstances, it may be better to help a sibling, knowing that they share 50 percent of your genes, if the cost to doing so is low and the benefit high. Or it may
This is the answer, from a selfish gene perspective. As a parent, my kids each have 50% of my genes, so I’ll want to share my time between them. As a child, I only share 50% of my genes with my siblings, but I share 100% of my genes with myself, so I’ll want to get more of my parents attention.
Obviously, it’s not a perfect correlation like that (would I sacrifice one sibling to save 4 cousins, or 16 second cousins (or however the math works out))? Probably not. But, in general, genes who were successful at getting more of their parents care and attention outcompeted genes that were less successful at that.
Often child behavior is described as competing for attention. The child isn’t necessarily in a competition with anyone or anything in particular, they just want more attention than they are getting. Most parents try to provide somewhat equal attention to their children, and some do show favoritism, but other than that siblings usually aren’t competing against each other. They are more likely competing against their parent’s job or other aspects of their parents life. It’s pure selfishness, which is to be expected from a child, especially a child feeling neglected in some way. Other than that, well of course kids will compete to determine who is faster, stronger, smarter, or better at delivering insults. That’s the kind of things kids do as much with other unrelated kids as they do with their siblings. When siblings are actually competing for their parents attention then the parents haven’t been doing their job.
This is inconsistent with many sibling studies. Most younger siblings will take complete opposite tracks than their older siblings to differentiate themselves. In some cases, if the older sibling gets good grades in school, the younger sibling will purposefully tank their grades to be different than the older sibling and receive differing attention from their parents.
And keep in mind that, in most cases, sibling rivalry isn’t completely cutthroat. When matters get serious, in most cases, siblings will cooperate, even at significant cost to themselves.
Again, wanting more or different attention from parents is not exactly a competition. Any sibling may want more attention than another but not necessarily as competition with a sibling. You even state the case where a child wanting more attention does not compete with their sibling and in fact would be throwing the game if it were a competition. Instead the child act in a different manner to get their parents attention. The term ‘compete’ is over used in this context. A child’s desire for parental attention does not have to be the result of anything a sibling does, and is usually the result of the parents failure.
If we’re talking humans - and up to a point. Baby birds, not so much.
Survival of the fittest is not baby bird competing with a cat; that’s a losing game. Survival of the fittest is baby bird 1 vs. 2 and 1 trying to push 2 out of the nest so the cat gets its meal and leaves the area. (simplistically speaking)
Evolution is not a grim reaper, it’s a grim sower, ‘letting’ most (all?) species create way more off-springs than needed for replacement (fish are the extremes, I think). Mindless and agency free evolution is so evolutionary successful, because this has been tweaked for hundreds of million years.
That’s what’s called the R reproductive strategy (and fish have nothing on oak trees, as far as that goes). Humans, however (and in fact most mammals) tend towards the K reproductive strategy, which consists of having only a few offspring, but investing heavily in their survival and success.
Right. The kids don’t yet have offspring, so the only strategy they have for propagating their genes is to survive until reproductive age. Mostly, that results in totally self-interested behavior, though with some degree of weighting based on the efficiency of spending resources. The parents have a different motivation; assuming their children aren’t a write-off, it’s in their interest to put all available resources into the existing batch. The only reason they have to act selfishly is if they think they can reproduce a lot more in the future if they manage to survive the present.
I guess I’ll defer to the OP to explain what they meant when referring to “compete”. I understand your point of view.
When sibling A tries* to position (physically, socially, psychologically) itself such that it acquires more of a necessary resource than does sibling B, that is the sense of ‘compete’ I mean.
*For some sense of ‘tries’ that needn’t require agency.
An example of something close to sibling competition: prevention of sibling creation:
Babies Cry at Night to Prevent Siblings
Though I take some issue with the use of “to” in the headline; surely that’s not the only or primary reason babies cry at night, but more of an ancillary benefit.
(It also inspires the question, probably for a different thread altogether: do humans, across cultures, mate mostly at night?)
How do you define a ‘necessary resource’? Specifically do you mean parental attention outside of providing food, shelter, and other such very basic necessities? In that case I think the phrase ‘competing for attention’ is quite common but blurs the question. An only child can seek attention from a parent in exactly the same way and for exactly the same reasons as one child with a dozen siblings. I think your question is about parental attention, not competition at all.
In many of the sibling studies that I’ve read, they mention only children will also seek out close friends that they will attempt to differentiate from as well as a means of developing a unique identity. While the only child isn’t competing for its parents attention away from a friend, it is competing for attention in general to be unique in its identity.
This make perfect sense. At the root of the issue is a child’s desire for parental attention. That could be an entirely selfish and unreasonable desire for all of their parent’s attention. Distinguishing ones own unique identity is a tactic to use in that approach, but so is any behavior to gain more attention including acting out in ways that are not at all a reflection of the child’s identity. A child may have the capacity to do so relative to siblings or friends, but would rarely be able to do so when the parents lack of attention is a result of their job, adult relationships, illness, or just disregard. Calling it competition collapses a lot of behavior to a simplistic explanation that may hide a more specific motivation.