Nonlin.org has a burning desire to discuss sexual selection. So, let’s.
The topic was tangential (though not entirely unrelated) to the evolutionary psychology thread. Nonlin was unable to restrain his contempt for his interlocutors, and so his final missive was guanoed. The opportunity to repost was declined, as guanoing is ‘censorship’ (in plain sight!) and a ‘white flag’ allowing nonlin to declare victory and strut around like … well … a peacock.
Now, we can’t expect too much from nonlin; they have no grounding in genetics, a distaste for the entire concept of selection, and indeed insist that genetics and evolution bear no relation to one another(!). But, I’m a compulsive responder. I realise not everyone finds these exchanges edifying.
Selection occurs when variants in a population are sorted by an environmental factor, such that one variant increases in frequency (and hence all others decrease) due to their relative performance in the presence of said factor. At the limit, this process results in fixation of a single variant: all other variants are eliminated and the trait becomes a characteristic of the entire species.
It is evident from the above that, if the environment changes in some way, such that there is no longer a factor maintaining the trait, it may itself be eliminated, since there is no longer a reward (in the currency of survival and reproduction) for its possession.
Now, ‘the environment’ here is not simply the inanimate portion. Other species form part of the environment of any given species, such that, for example, predators and prey may each undergo adaptations tuned by the presence of the other. Remove the predators and birds may become flightless, or camouflage become unnecessary.
In the specific case of sexual selection, the ‘environment’ is provided by members of the same species. Given that, in obligate outcrossing sexual species, mating partners are a vital part of the reproductive chain, the potential arises for a feature to be maintained by mate preference. Assuming this ‘preference’ itself to be under genetic control, then both preference and trait are passed into the genomes of both sons and daughters. The genes are only expressed in one gender, but carried by both. Mothers may pass the preference for large-tailed mates to their daughters, but also, cryptically, to her sons and hence to their daughters too. Likewise, her mate’s large tail genes may pass to both her sons and her daughters’ sons.
Now, a potential conflict arises with other modes of selection. The feature – say, the elaborate tails of male peacocks – may hinder the animal in the more general challenges of survival. Nonlin astutely observes that, without the layer of sexual selection, the feature would not exist: it is maladaptive. This is hardly fatal to the theory, however. It is entirely in accord with it; selection depends on environment, which includes both predators and mates. Change that environment – remove female preference – and losses to predation would likely see elimination of the feature (amusingly, nonlin here is making an argument for selection, not against it). Nonetheless, given coexistence of feature and preference, it requires only that losses to predation are offset by greater gains in mating success. If big-tail males get more action despite the cumbersome tail, that is sufficient. Indeed, it can be seen as a mark of general health and quality; the passing of various tests before a suitor can win the hand (or wing) of fair lady is a classic of literature! To complete the analogy, we need only imagine the story littered with the corpses of the failures …
Here, shorn of most of its bile, is the guanoed quote:
Me: That ‘preference’ [of females for certain male qualities] generates a competition.
Nonlin: False. The peacock is born the way he is. There’s nothing more he can do.
Nonetheless, there is a competition between different males, ‘born the way they are’, for mates.
Furthermore, that’s why we have definitions (as bad as they are), so people like you don’t start making up stuff. Look up “sexual selection”.
Nothing to say: I just left that in as a classic example of reflexive internet blowhardery. ‘Look up X’. I saw an exchange where someone tried to mansplain the Good Friday Agreement in similar fashion. Her classic response was to post a picture of her grinning, holding up her book entitled “The Good Friday Agreement”.
Me: The genes involved in mate preference are not the same genes as those involved in generating elaborate tails.
Nonlin: The genome is a package. So yes, it selects itself which is self referential and stupid. Even “natural selection” is not that stupid in this limited sense (fully stupid otherwise).
There is no conflict between ‘the genome is a package’ and ‘one part of the genome acts upon another’. That action can be intracellular – for example, DNA polymerisation involves precisely that, so I suppose replication is self-referential and stupid. But it can also involve actions at a distance, between different instances of the genome. The genomes of male and female are indeed separate genomic ‘packages’.
ETA – it’s worth mentioning the rival, Design, explanation in this context. We are presumably to suppose that female ‘choice’, and the chosen feature, were both designed. Why? Firstly, we’d have to asked if Designed Big Tails do better in mating, despite their costs. If they don’t, they’re just a whim – a presumed costly feature added for funzies. If they do, the objection to net selection disappears, and we have the extra question of why females were ‘designed’ to have that filtering preference. It seems an odd thing to do, pitting design against design for no general benefit, assuming (as is generally the Assumption in our Christian-dominated halls) a single designer.