Yeah that's (to me) a more accurate framing, also evolution is bad at revisions so even if there are minor disadvantages to a setup so long as it's not affecting your ability to have and raise kids it's basically completely absent as far as evolution is concerned. For example there are some wild inefficiencies in body layout left over from fish body patterns where the nerve from the brain to the voice box wraps down around your aortic arch because the relative position of the throat, brain, and heart were very different in fish so the path it took then was more direct. It happens in humans and most hilariously in giraffes where it goes all the day down their enormous necks.
That remains as it is because it's very difficult to evolve away from. Evolution is very good at chasing and sticking around local optima. Big changes are risky.
They can be detrimental too, especially if they're linked to beneficial traits. The test is ultimately whether or not the harm done is sufficiently disadvantageous that it interferes with reproductive fitness. Baldness is arguably detrimental, but it's linked to a bunch of recessive genes that function in other ways, and it doesn't impact us until we're likely to have already reproduced.
Peacocks with their giant tail feathers are my favorite example. They make flying really difficult, but they make attracting female mates much easier. The reproduction need wins.
I don't know if I would consider it especially difficult for them. It is obviously not convenient but when I had peacocks they would still fly way up in some tall pine trees to roost even with a full tail without too much trouble. That said these were domestic peacocks so they didn't have to fly very far at all for everything they ever wanted, wild peacocks might have to go farther.
and not even that, I'd narrow it further to not detrimental before and during the prime reproductive periods of a species. After that period, detrimental traits are totally fair game and more dependent on technology, culture, and family care dynamics. Heart disease later in life caused by genetic predisposition to high cholesterol isn't something people generally select for or against in a partner, but its effects happen later in life well after people have children so it passes on.
> Heart disease later in life caused by genetic predisposition to high cholesterol isn't something people generally select for or against in a partner, but its effects happen later in life well after people have children so it passes on.
That depends. It can still affect genetic fitness if it affects an individual's ability to confer benefits on their descendants. Of note: most of the most wealthy and influential people in our society are beyond their reproductive years (not technically true for men, but mostly true in practice).
Even if yawning in public affected sexual fitness: how long has it been socially impolite to yawn in public? Evolution takes a rather long time in species with long reproductive cycles. Almost all mammals yawn, it would take significant genetic changes to breed that out of us. That doesn't happen overnight.
No, it isn't. It can be socially impolite to yawn unexcused, when someone is talking to you, as it has come to be interpreted as boredom rather than tiredness or similar. But it isn't inherently impolite to, for instance, yawn when walking down the street, or in a setting where someone isn't talking to you.
Is that the right criteria? A trait must be completely, 100% disqualifying as a mate or else it sticks around?
Our ancestors used to have tails. We no longer have tails. Plenty of people wear artificial tails today and get laid, it's not a 100% disqualifying trait
Our primate ancestors required tails so they could effectively move around on trees. A tree dweller without a functional tail is slower and has a harder time gathering food and escaping from predators. That's a very strong selection pressure that ends up maintaining the tail.
When the woods in eastern Africa changed into savannah, we shifted to two legs and adopted a persistence hunting strategy. The tail became useless, even a liability, and mutations that resulted in reduced tails were not selected against anymore.