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Until some other species takes over your ecological niche.
I seem to remember hearing about a gene in mice that would ensure that it always gets copied into the offspring if present (leading to rapid growth in the gene pool) but had the unfortunate effect that homozygotes are sterile.* Under random mating, you can calculate the population levels at which the gene frequency is stable,** but under non-random mating, a group where 50% of the parents have this gene could totally annihilate itself (as it would be possible to ensure that every child in the next generation is a carrier, and thus the generation after that will be totally sterile).
But consider this gene without a drawback: if one parent has at least one copy, then the child will, and if both parents each have at least one copy, then the children will have two copies, but the gene is fitness neutral in all permutations. Then we can calculate how many generations it will take for the gene to reach fixation, given random mating.
*Suppose the mechanism was that it would break the other chromosome. This means you're the only option--unless the other chromosome had the exact same idea, and now there aren't any functional chromosomes.
**As it turns out, the heterozygote advantage and homozygote disadvantage are both so strong that the only stable levels are 0 and 1. If you drop the heterozygote advantage to something more likely, like a heterozygote having a 55% chance of passing it on to a child, then you get a more interesting answer.
This is a fundamentally mistaken way of looking at evolution. The only important thing is whether it is a selective advantage or disadvantage! Populations roll down the selection gradient, and the assumption that population sizes are the same from year to year is a feature of mathematical models, not reality.
You are good at lowering the probability I give to this hypothesis, and I thank you for that, but it is stil not 0.
First about the second point - my point is more like selective advantages do not mean the fitness of the group, or even the fitness of the parents to be maximized, but solely that of the propagation of the gene in descendants. So, from that angle, a gene killing some parents but still making an animal more sexually succesful can still confer a selective advantage. Depending on the ratio of this two of course. My point is precisely that on the ... (read more)