The individual would still have other relatives who would pass on the genes, like sisters, brothers, other family members. If the individual's sacrifice helps the group survive, their genes would be passed on in those relatives. Also note that the gene would only be activated under a certain set of circumstances, so individuals could have the "self-sacrifice" gene and pass it to their children, even if they never encountered the set of circumstances that would induce suicidal ideation themselves.

I believe there is similar thinking for genetic passing of traits like homosexuality.

That explanation doesn't make sense to me. Your brothers/sisters etc. have similar genes, but they don't have your genes. The theory of evolution is that the most fit genes propagate. So if your brothers/sisters propagate but you don't, then your brothers/sisters genes (along with whatever mutations they might have) are being selected over yours, just as if you had some mutation that made you overall less fit.

It's called kin selection and I think it's generally accepted within scientific community to be a real phenomenon.

https://en.wikipedia.org/wiki/Kin_selection

That addresses my question exactly, thanks!

The most fit genes propagate, not the most fit individuals. Your siblings have many of the same genes that you have. Say there is a gene A that will result in some individuals not reproducing, but will result in more members of their group reproducing. Now say there is 1 group where the members of the group have gene A, and another group where the members don't have gene A. Over time the group with gene A will reproduce more than the group without A, resulting in more copies of A in the general population.

Even if some individuals in the group do not reproduce, their relatives in the group do reproduce. So say 1 person self-sacrifices and does not reproduce, and as a result of their sacrifice 10 others in the group survive and reproduce that would not have been able to if the first individual had not self sacrificed. The family all has gene A, so this results in a net gain of 9 individuals with gene A. So the amount of people with gene A increases, even though some individuals with gene A potentially do not survive and reproduce.

If you want to learn more about this kind of thing, look into "Selfish Gene Theory".

I guess this works if you separate the idea of "fit for a particular situation/environment" for "fit in general."

Suppose we did not separate these things. In that case, for an entire group to have A, that implies that some ancestor of that entire group had A. But this contradicts the premise that the gene makes people less likely to reproduce.

It works if you accept the idea that genes which are fit in some situations are less fit in others. In that case you could have a person who developed this mutation of feeling suicidal when they feel useless, but it doesn't "activate" because they aren't in a situation where they feel useless. But once a whole group has this gene, then your theory of propagation through siblings/cousins is more plausible.

Not every trait that exists has to be selected for. It just has to not be selected against enough for it to be completely wiped out. Some people procreate before they commit suicide, even those that don't would have relatives who might have been spared by different circumstances, or a slightly different mix of genes.

Sometimes traits are related, or negative traits are only manifest in a recessive manner. In such a way positive traits can be selected for, which have a consequence of a negative trait being present in a population.

The example frequently citied in this area is sickle cell anaemia, which can be inadvertently selected for in areas where Malaria is common. Having one 'bad' gene protects the person from Malaria, having two means that one has sickle cell anaemia.

This means that people with a single gene are more likely to survive, and hence pass on their gene, but this sometimes manifests as someone with sickle cell anaemia. See https://en.wikipedia.org/wiki/Sickle-cell_disease#Epidemiolo...

It's easy to make evolutionary just-so stories and they're usually worthless anyway, but here's my attempt at one: as an animal, if you reach a certain age and are not already a parent, it means you're deficient. It's better for the gene pool if you die without reproducing. If you're a parent and you did all that was needed for the offspring to survive the early development period, you're no longer needed and probably better off dying instead of consuming resources your children need.

Yes I generally hate evolutionary just-so stories.

> if you reach a certain age and are not already a parent, it means you're deficient. It's better for the gene pool if you die without reproducing.

This explanation makes no sense to me. Evolution doesn't select for the overall gene pool AIUI, it selects for fit individuals. I can't see how, even in theory, this explanation would be plausible.

> If you're a parent and you did all that was needed for the offspring to survive the early development period, you're no longer needed and probably better off dying instead of consuming resources your children need.

This explanation sounds at least mathematically plausible to me.

How does this explain the higher rate of suicidal ideation/actions in depressed adolescents who are at their biological prime for reproduction?

I don't know. Except maybe that biologically they're supposed to have children instead of sitting in school and waiting for marriage, home and a job.

No idea what this means if you're a male. Males are fertile forever basically, so there isn't some "optimal" age to have offspring.

By your logic, males should be continuously fathering offspring throughout their lives, as soon as they reach puberty.