Discussion at the time: https://news.ycombinator.com/item?id=13027132
They are saying an individual can only mate with a quarter of the population, but it's obviously incorrect, as the pre-mutation birds can mate with both mutated and unmutated opposite sex.
The reason cross-morph pairs are observed more often as the mutated birds are more sexually aggressive and quickly round up unmutated opposite sex.
Even if the tan/tan is still physiologically possible it may be the case that they still won't mate even if there are no white present at all due to required mating signals being missing.
I.e., I would guess that plants that have easy seed propagation have less complicated sexes, but I don't know.
Or maybe it's just irrelevant for birds. Birds appear to break many laws of nature other animals have to abide by. They fly, they move where they want. They stay close to humans, observe them, and easily avoid them. They're amazingly energetic for how big they are. They migrate extremely far. They don't have to commit to anything except when rearing young.
Common ideas are commonly wrong. Non-useful ones only disappear reliably if they're selected against. Otherwise, you get goose bumps, or piloerection in humans: We don't have enough hair over most of our bodies for erecting it to do any good, but we still have all the structures to erect it anyway, because none of our ancestors lost any of them even as they became useless.
ie., evolution is starting with a bike and turning it into a car
it is not "starting with raw materials" and shaping them
So pretty much every life form is highly non-optimal wrt their environments.
By making procreation harder to achieve, you intensify the selection effect, since only the fittest individuals will be able to achieve it. So maybe it can be thought of as a kind of extra layer of "culling of the weakest" built into the genetics of the species?
Indeed it's one definition of a species that it's a population that can mate within it's group. So if they can no longer breed with each other, are they same species or not?
So it's not speciation, any more than sexes themselves are speciation.
This alone doesn't contradict the two-species theory. It could be that white-M + tan-F is species #1, and white-F + tan-M is species #2. Sure, it sounds weird, but not nearly as weird as the idea of 4 sexes, IMO.
> (And the offspring are about half white-striped and half tan-striped.)
Now, this is the important part. As I understand it, the offspring of "species #1" could be "species #2" or the other way round. This indicates that #1 and #2 are the same species after all.
