Can selective breeding effect sexes differently?

jpanhalt

Joined Jan 18, 2008
11,087
The question has been settled by science:
Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5775321/
Breast development occurs during puberty in girls, after which the enlarged breasts are retained throughout adulthood. Breast size in adult women is associated with perceived femininity and is sexually important in many cultures1,2. Apart from being a potential marker of health and fertility from an anthropological point of view, breast size has been shown to affect women’s quality of life and well-being in many ways – socially, psychologically and physically3. For example, several studies on sport and exercise participation in adolescent girls revealed large breasts to be a cause of physical strain and a major reason why they do not take part in physical activity4,5. Back problems are also more common among women who are more well-endowed6. In terms of breast health, breast size has been studied extensively as a risk factor of breast cancer, but the results are inconclusive7.

Breast size is a highly heritable trait. A twin study previously estimated the heritability of bra cup size to be 56%8. Several genome-wide association studies have also identified common genetic variants associated with breast size9,10. Asian women are typically less well-endowed11,12 than women of Caucasian ancestry.
In my non-random sampling, I concur. ;)
 

WBahn

Joined Mar 31, 2012
30,301
There is no theoretical reason that I know of that selective breeding (allelic selection) could not create more distinctive sexual dimorphism than we currently see.
I think that is consistent with what I said (correct me if I'm wrong). Basically, what I said (in similar terms) is that while there are SOME traits that selective breeding could make more sex-linked, it is probably that we would have a hard time doing it for MOST traits. So if you just picked a trait (tail length was an example given), it is unlikely that you could make a big difference in that trait between males and females via selective breeding. But you might get lucky.

Assuming the above is reasonably correct, the next question is how do we identify which traits have the potential to be influenced by selective breeding to achieve the desired sex-linked characteristics? My (very naive) speculation would fall along two lines.

First would be to observe which traits already exhibit at least some level of being sex-linked. It would seem those would offer the highest potential of being susceptible to modification via selective breeding. For instance, size differences. What would happen if you focused on breading the largest females with the smallest males? Could you manage to artificially reverse the usual difference? Or is it too strongly embedded in the mammalian DNA? If you could reverse it, it would be interesting to see how hard it would then be to reverse it back. That might shed some interesting light into what is truly intrinsic versus what has merely been selected for over time. My guess is that if you pick a random trait that has no discernible sexual dimorphism that you will probably (but not necessarily) face an uphill battle as I suspect that traits that have any significant potential for such dimorphism would probably already exhibit it to some discernible degree.

The second would be to use our knowledge of the mapping of traits to inheritance to identify which traits could likely be swayed by selective breeding. That's about as far as I can go down that path because I don't have any idea of how strong our knowledge is in that area and what the capabilities and limitations we currently have.
 

jpanhalt

Joined Jan 18, 2008
11,087
I have no interest whatsoever in breeding humans. I prefer the natural selection process most of us have been through.

As for telling cows from bulls, I have never been confused. Now, telling bucks from doe is a little more difficult. Doe can have antlers.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,839
I have no interest whatsoever in breeding humans. I prefer the natural selection process most of us have been through.

As for telling cows from bulls, I have never been confused. Now, telling bucks from doe is a little more difficult. Doe can have antlers.
Too bad we can't make chickens grow horns.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,839
I'm probably about to get my own thread locked, but what got me started on this line of thought was listening to another iteration of the debate around trans/bio male/female, postmodernist muddying of the waters with "social constructs" and cheering on biological males who dominate women's sporting events. Many are making claims that there are no physiological differences between men and women (apart from an appendage or two). I was playing a bit of devil's advocate, thinking that maybe instead of making such obviously absurd claims they should instead insist that the average man is bigger, stronger, more prone to take risks, with faster reflexes and more aggression than the average woman due to a long history of sexual selection propagated by the patriarchy. That men, in their unquenchable lust for dominance, have over many hundreds or thousands of generations, selected mates who were smaller, weaker, and subdued with submissive tendencies, so as to maintain a position of power over them.

That claim would fit better with the [man = bad] and [woman = victim] narrative, and by what I've read here and in my own research it would probably actually have some element of truth to it. It would be much easier to prove in the court of public opinion. But I doubt it would ever gain any traction in those circles because it would mean:
1. Acknowledging the differences they've already denounced.
2. Admitting defeat in a game started before our own species.
3. There is obvious solution: women, start pursuing beta males. Bang that pale network analyst from work (I'm sure you're in here, no offense); the one most people assume to be gay but he's actually not - you know, the one who isn't toxically masculine. And that just ain't gonna happen, because everyone knows that alpha males are what women are programmed to seek out*. Probably by men's nefarious design. Damned men, sheesh.

*Not that programming can't be overridden, it can, but usually isn't.
 
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WBahn

Joined Mar 31, 2012
30,301
I don't know to what degree human females have historically been attracted to the strong, masculine males. What constitutes "beauty" is quite variable and tends to reflect current conditions pretty heavily. At various times in history during prolonged periods of famine, "plump" people were found to be desirable because they were the ones that had the ability to find/obtain adequate food. So if you think about much of human history, the ones that were more likely to survive and protect and provide for their mates and offspring were not the strong, athletic ones, but the smart ones. Humans just are not well adapted at all to rely on brute strength to survive in nature, we have had to rely on our wits to do so. Imagine taking two groups of a thousand humans and putting them on identical islands having a mix of flora and fauna both benign and hostile. The first group consists of people that are the the lower end of the intelligence spectrum but upper end of the athletic spectrum, with the other group is the opposite. My money would be doubled down on the latter group to survive, even if the two groups were put in direct competition and conflict at some point. Of course, the odds of survival would go up significantly for a third group that had a broad mix of people across the spectrum of both characteristics, even if you precluded the possibility of any of them being at the upper end of both.
 

jpanhalt

Joined Jan 18, 2008
11,087
I was playing a bit of devil's advocate, thinking that maybe instead of making such obviously absurd claims they should instead insist that the average man is bigger, stronger, more prone to take risks, with faster reflexes and more aggression than the average woman due to a long history of sexual selection propagated by the patriarchy. That men, in their unquenchable lust for dominance, have over many hundreds or thousands of generations, selected mates who were smaller, weaker, and subdued with submissive tendencies, so as to maintain a position of power over them.
Women have advantages too. They are making a mark in drag racing as drivers (e.g., Courtney Force) and horse racing as jockeys. Lighter weight and smaller size can be an advantage.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,839
I don't know to what degree human females have historically been attracted to the strong, masculine males. What constitutes "beauty" is quite variable and tends to reflect current conditions pretty heavily. At various times in history during prolonged periods of famine, "plump" people were found to be desirable because they were the ones that had the ability to find/obtain adequate food. So if you think about much of human history, the ones that were more likely to survive and protect and provide for their mates and offspring were not the strong, athletic ones, but the smart ones. Humans just are not well adapted at all to rely on brute strength to survive in nature, we have had to rely on our wits to do so. Imagine taking two groups of a thousand humans and putting them on identical islands having a mix of flora and fauna both benign and hostile. The first group consists of people that are the the lower end of the intelligence spectrum but upper end of the athletic spectrum, with the other group is the opposite. My money would be doubled down on the latter group to survive, even if the two groups were put in direct competition and conflict at some point. Of course, the odds of survival would go up significantly for a third group that had a broad mix of people across the spectrum of both characteristics, even if you precluded the possibility of any of them being at the upper end of both.
One of the things I read yesterday on the topic of sexual dimorphism was about how some of the dimorphic traits do not seem evolutionarily beneficial. For example the pheasant and peacock. The males are brightly colored while the females are drab. The males have anti-camouflage, and the result is that they have half the lifespan as females in the wild. But for them, long life is not the marker of success. Reproduction is.

Maybe it isn't survival of the fittest OR the most intelligent, but survival of the most prodigious reproducers. Given the time it takes us to reach sexual maturity however, I'm inclined to agree with you, at least in the case of humans.

I suppose the shift the sexual selection process could have already taken place, a few thousands of years ago. Women started favoring brains over braun and the next thing you know we had written language, followed closely (in evolutionary perspective) by online electronics forums.
 
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WBahn

Joined Mar 31, 2012
30,301
Women have advantages too. They are making a mark in drag racing as drivers (e.g., Courtney Force) and horse racing as jockeys. Lighter weight and smaller size can be an advantage.
I wouldn't think that being smaller would be good at all for a jockey. My understanding is that if a jockey is below the target weight that lead weights are added to the saddle to make up the difference and that this is a significant disadvantage because it is unsprung weight.

I know several forms of auto racing require either the total vehicle weight to be a specific value and/or the weight of the driver to be a specific value, adding deadweights to make up the difference.

It was claimed for some time that women, on average, had greater G-tolerance than men. I don't know what the current thinking is, but back while I was on active duty (mid 80s) there was an article I read that indicated that if you matched women and men by height and weight that there was very little difference, but that height had a very strong negative influence while weight had a fairly significant positive influence (which is why a significant fraction of fighter pilots tended to be short and stout, often with high blood pressure). Thus women of the same height tended to do worse because of lower weight, but women overall did better because of the overall lower height overcoming the effect of lower weight as a group.
 

Thread Starter

strantor

Joined Oct 3, 2010
6,839
Let's be careful about taking this into a political/contentious realm.
Women have advantages too.
Of course they do. But it seems those arguments aren't heard as often as they once were. What once was an argument of [men are better at some things] vs [women are better at some things] is currently shifting into an argument of [men are better at some things] vs [women are absolutely indistinguishable from men in every conceivable way, you sexist pig. And now that we have sex change operations you can literally suck it, too].

There are so many things a woman is better at. I am happy to celebrate them. But that isn't what got me started on this line of thought, so I didn't feel compelled to discuss it in my post that started with "what got me started on this line of thought..."
 

jpanhalt

Joined Jan 18, 2008
11,087
I wouldn't think that being smaller would be good at all for a jockey. My understanding is that if a jockey is below the target weight that lead weights are added to the saddle to make up the difference and that this is a significant disadvantage because it is unsprung weight.
Jockeys of my era were short men of small frame:
1606139237319.png

Willie Shoemaker is the short guy on the left. Of course, the only horse racing I have seen was at Santa Anita and the Preakness (once).
 

WBahn

Joined Mar 31, 2012
30,301
Jockeys of my era were short men of small frame:
So? Virtually all jockeys are short. The context is the claim that women jockeys having and advantage over male jockeys because they might be smaller and lighter. I don't think that is the case because a lighter jockey is going to have additional deadweight added to the saddle to bring them up to regulation weight. IIRC, the regulation weight for the rider is something like 110 pounds. Whatever it is, riders above that weight don't get many rides while riders below that weight are penalized by having deadweight added to the saddle, so most jockeys work very hard to stay at exactly that weight.

Since that weight is a very common weight for many healthy women, I've wondered why the sport isn't dominated by female jockeys. In fact, I would expect a female jockey to be taller than a male jockey of the same height (on average) which would result in a smaller unsprung weight and a bit of an advantage. I don't know the answer. Is it discrimination? At some point that was probably a major factor, but I don't think that's been a huge factor for some time. I doubt it has anything to do with a difference in physical ability. Something about the sport that just doesn't attract women for some reason? Seems a bit unlikely given how well women are represented in many other equestrian sports and equestrian events are one of the few areas of sports competition where women and men often compete directly without men's and women's divisions. Emotional or mental differences? Perhaps, but I wouldn't think so. Even if it's the case that women aren't, on average, as attracted to highly competitive sports there's plenty of women competing in many other highly competitive sports that it's pretty clear that there's enough of them out there even if the overall fraction might be lower. One possibility that I can imagine is if (if) women are less likely to enter into things that they feel uncomfortable at while men are less concerned about that. I've heard that claimed and, if it's the case, then I could see it taking a long time for women to gain a foothold in a male-dominated environment. In the handful of female-dominated areas that I can think of, such as nursing, I think that men possibly have tended to be less reticent about entering that realm once it was opened up.
 

justtrying

Joined Mar 9, 2011
439
So? Virtually all jockeys are short. The context is the claim that women jockeys having and advantage over male jockeys because they might be smaller and lighter. I don't think that is the case because a lighter jockey is going to have additional deadweight added to the saddle to bring them up to regulation weight. IIRC, the regulation weight for the rider is something like 110 pounds. Whatever it is, riders above that weight don't get many rides while riders below that weight are penalized by having deadweight added to the saddle, so most jockeys work very hard to stay at exactly that weight.

Since that weight is a very common weight for many healthy women, I've wondered why the sport isn't dominated by female jockeys. In fact, I would expect a female jockey to be taller than a male jockey of the same height (on average) which would result in a smaller unsprung weight and a bit of an advantage. I don't know the answer. Is it discrimination? At some point that was probably a major factor, but I don't think that's been a huge factor for some time. I doubt it has anything to do with a difference in physical ability. Something about the sport that just doesn't attract women for some reason? Seems a bit unlikely given how well women are represented in many other equestrian sports and equestrian events are one of the few areas of sports competition where women and men often compete directly without men's and women's divisions. Emotional or mental differences? Perhaps, but I wouldn't think so. Even if it's the case that women aren't, on average, as attracted to highly competitive sports there's plenty of women competing in many other highly competitive sports that it's pretty clear that there's enough of them out there even if the overall fraction might be lower. One possibility that I can imagine is if (if) women are less likely to enter into things that they feel uncomfortable at while men are less concerned about that. I've heard that claimed and, if it's the case, then I could see it taking a long time for women to gain a foothold in a male-dominated environment. In the handful of female-dominated areas that I can think of, such as nursing, I think that men possibly have tended to be less reticent about entering that realm once it was opened up.
I love equestrian sports and used to do horseback riding. Jockey weight for a woman is very low. It is not a common weight at all, i am 5'4 and 108 lbs. This is basically size 0/xs. There are not a lot of women my size. In the States I have to buy clothes in childrens section. For me it would be very challenging to convert the very little fat that I have left into muscle to gain strength required to control a horse. This is biology - nature wants women to maintain a fat reserve, it is less of an issue for men and the conversion back and forth happens easier, men gain muscle quicker (loose it quicker also). Further reading shows that women are not really given the opportunity to ride so that is the other piece.
 
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