Pondering such inane imponderables exercises our brain just as efficiently as musing
on the weightier issues.
I myself have long wondered why doing this can only be done by females,
what extra bones have males got that prevents us from gazing at the backs of
our own knees ? [..]
A few musings:
1) What evidence do you have that this is consistent across all sexed species? Humans, yes, but you're explicitly referring to all sexed species. Dogs, cats, elephants, etc, etc. Even plants.
2) In humans, what evidence do you have that it's consistent across all ages? Adults, yes, adolescents, yes, but children and babies?
3) In adults, there's a
tendency for women to be more flexible than men. That could be explained by tendencies towards physiological differences and adaptations to different circumstances (which would also be a factor in tendencies towards physiological differences). The most obvious one is childbirth imposing different selection pressures. There are some structural differences in the pelvic area as a result, enough to make it possible to reliably determine a person's sex from their skeleton on just that basis. Roughly, childbirth and the different roles of men and women for almost all of the existence of humanity and the ancestors of humanity have imposed slightly different selection pressures on men and women which has resulted in a strong tendency for slightly different prioritisation of strength and flexibility.
4) Maybe there's a gendered trend for medical conditions that allow an unusually large degree of movement. What's sometimes called "double jointed". Which looks startling but comes with problems.
It's not universal. When I was the age of the woman in the photo, I might well have able to do that. I was flexible enough to contort myself in weird ways like some sory of human knot sculpture. I haven't grown any extra bones since then, but I have aged and I've grown a lot more muscle (and fat). I was a lot more gracile when I was young, which was part of the reason why I was often mistaken for a woman.
EDIT: I had a look at a summary of hypermobility and wasn't suprised to find that I have a few of the more minor symptoms. Good thing for me that it's only that much - it can cause really serious problems. And it is more common in women than in men.
