![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
guslfrom the odd pages of a philosophy paper titled "Prediction":
In other words, the genes are using a 50/50 mixed strategy in the game of "choose the baby's gender". (remember game theory?) (note: this "choice" is always made through the sperm: the choice of mix between X-sperms or Y-sperms, so any genetic disposition to produce more males or females must be passed on to male babies)
In particular, if male children died more than female children, we should expect that more males will be born.
Likewise, if male foetuses+children died more than female foetuses+children, we should expect that more males will be conceived. I would like to see actual statistics on this... or maybe we could "postdict" the infantile death rates of previous centuries, if we observed a small deviation in the number of conceptions in some native populations today.
I used to think that we should expect to have more females (because one male can fertilize many females), but this argument convinced me.
Of course, if we did have an imbalance in the sex ratio, the parents' genes would need enough time to "know" about the sex ratio before the countervailing pressure made any effect (it's not clear how many generations would be needed for the right mutations to appear). In particular, genetic adaptation will not solve China's female-deficit anytime soon: it will take many generations.
But Fisher's argument doesn't account for population selection:
(1) populations with more females could have more children, or (2) a greater female-to-male ratio could promote peace. Both mechanisms would promote population growth, but the selection effect is on the level of the whole population, which is much weaker than individual selection: in such populations, a male child's expected number of children will be higher than a female child's... so grandparents that make more boys will be more successful. This will tend to bring the ratio back to 1:1, even in a growing population.
But it would be interesting if we found that individuals from some recently "exploded" populations (think poor countries) were found to be genetically more likely to produce more daughters than sons. It would have to be because some segments of the population were growing faster by producing more adult females than adult males (possibly due to a sudden decrease in female infant mortality or, a cure of male-child-promoting diseases, such as we might expect from the Chinese population if they suddenly cure hepatitis B, after having enough generations with it to adapt their child-sex-production-ratio).
These arguments can get pretty involved, and I'm feeling insecure about my reasoning here. Do you see the appeal of formalizing such arguments into a logical system? What about the appeal of diagrammatic representation of these hypotheses and speculations as an argumentation map, instead of a 1-dimensional text full of nested parentheses?
These sort of arguments count as qualitative reasoning, don't they?
This argument in particular, due to being so meta (not atypical in arguments about evolution), where individual genes are being selected on the basis of the genes of the whole population, makes me want to formalize it in something like epistemic logic.
[About Fisher's explanation]
Too briefly, the explanation is that (assuming equal parental cost to
produce offspring of either sex, ignorance of offspring quality, and setting aside
complications), no matter what the mating system, a parent will spread more copies of its
genes by producing offspring of the less numerous sex: since every successful mating
requires the genetic contribution of exactly one member of each sex, members of the less
numerous sex are more easily able to obtain multiple successful matings, be more choosy
about mates, or enjoy whatever reproductive advantages members of that sex enjoy in the
mating system. Even if a species' mating is structured such that a few successful males
do all the mating and most males do not mate at all, when males are less numerous than
females a parent will do better on average by producing sons with a proportional chance
of being one of the lucky few than daughters who are guaranteed to mate. Therefore, it
pays to produce members of whichever sex is more rare, ensuring strong selective
pressure against any mechanism that favors producing male offspring over female or vice
versa
In other words, the genes are using a 50/50 mixed strategy in the game of "choose the baby's gender". (remember game theory?) (note: this "choice" is always made through the sperm: the choice of mix between X-sperms or Y-sperms, so any genetic disposition to produce more males or females must be passed on to male babies)
In particular, if male children died more than female children, we should expect that more males will be born.
Likewise, if male foetuses+children died more than female foetuses+children, we should expect that more males will be conceived. I would like to see actual statistics on this... or maybe we could "postdict" the infantile death rates of previous centuries, if we observed a small deviation in the number of conceptions in some native populations today.
I used to think that we should expect to have more females (because one male can fertilize many females), but this argument convinced me.
Of course, if we did have an imbalance in the sex ratio, the parents' genes would need enough time to "know" about the sex ratio before the countervailing pressure made any effect (it's not clear how many generations would be needed for the right mutations to appear). In particular, genetic adaptation will not solve China's female-deficit anytime soon: it will take many generations.
But Fisher's argument doesn't account for population selection:
(1) populations with more females could have more children, or (2) a greater female-to-male ratio could promote peace. Both mechanisms would promote population growth, but the selection effect is on the level of the whole population, which is much weaker than individual selection: in such populations, a male child's expected number of children will be higher than a female child's... so grandparents that make more boys will be more successful. This will tend to bring the ratio back to 1:1, even in a growing population.
But it would be interesting if we found that individuals from some recently "exploded" populations (think poor countries) were found to be genetically more likely to produce more daughters than sons. It would have to be because some segments of the population were growing faster by producing more adult females than adult males (possibly due to a sudden decrease in female infant mortality or, a cure of male-child-promoting diseases, such as we might expect from the Chinese population if they suddenly cure hepatitis B, after having enough generations with it to adapt their child-sex-production-ratio).
These arguments can get pretty involved, and I'm feeling insecure about my reasoning here. Do you see the appeal of formalizing such arguments into a logical system? What about the appeal of diagrammatic representation of these hypotheses and speculations as an argumentation map, instead of a 1-dimensional text full of nested parentheses?
These sort of arguments count as qualitative reasoning, don't they?
This argument in particular, due to being so meta (not atypical in arguments about evolution), where individual genes are being selected on the basis of the genes of the whole population, makes me want to formalize it in something like epistemic logic.
![[identity profile]](https://www.dreamwidth.org/img/silk/identity/openid.png){kind=small}
(no subject)
Date: 2005-07-26 07:32 pm (UTC)Btw, I suggest you delete your email address from here (spam bots), and post the comment again, without the email.
Viola
Date: 2005-07-26 07:36 pm (UTC)During periods of rapidly growing populations the balance of the two pressures is, I guess, tipped in favour of natural as against sexual selection. (though I may be wrong.) I'm also fairly sure that, during periods of prolonged stress (e.g. war/famine), the ratio tends to change, and an 'emergency strategy' of producing more of one sex (females, I think) than the other kicks in. (Again, I need to check my unreliable memory against the facts here.)
My understanding of the fundamentals of sexual dimorphism is that, where the sex ratio between sexes is 1:1 (Fisher's ratio); both 'maleness' and 'femaleness' are, on the average, equally successful genetic strategies. Males (in most species) are high-risk(0.1), high-stake(10) strategies; and females (in most species) are low-risk(1), low-stake(1) strategies.
Have you read that one of the measures biologists use to gauge levels of sexual selective pressure is to observe the scale of differences between females (which, in most species, are optimally sized for their environment) and males (which tend to be oversized relative to their environment, due to sexual selective pressures... thinking about it, I'm fairly sure it'd be females who are produced in greater proportions during periods of environmental hardship, as they tend to be more optimally selected for the environment). Often, sexual-selective arms races emerge in males which make them misshapen and suboptimal from a natural selective perspective: some species of primate have males who are larger overall than females as males compete with each other directly; others have very large testicles, trying to outproduce each other in sperm, so that when they mate with females it's more likely they, and not a rival, will be the one to inseminate.
Sorry if I'm babbling. I'd be really interested in discussing the issue further with you though; as the logical principles of sexual dimorphism is something I'm very interested in getting clear in my head; and because I'm due to begin a PhD which involves creating computer simulations of social phenomena, and I'd like to get some practice at converting qualitative postulates into programmable axioms.