Is arm length sexually selected?

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Fishnut
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Is arm length sexually selected?

Post by Fishnut » Wed Nov 04, 2020 1:20 pm

I just found this article and it's a sent my skeptical senses quivering. It looks like b.llsh.t but I'm nowhere near the right frame of mind to do a good deconstruction job. Looking at the original research (open access), the abstract begins,
Growing evidence suggests that human males have been sexually selected for violent contest competition.
But I can't find this backed up with evidence in the main body of the paper (though I may just not be looking hard enough).

I get really suspicious of papers which presume that fighting ability is all women looked for in partners back in prehistoric times. For one, it assumes that communities were constantly fighting which, from my reading, isn't at all true. It also assumes that women are inherently attracted to the strongest and most aggressive men and while I definitely know women who are, for many that's actually a turn off. And unless you're claiming that the majority of relationships were non-consensual I think you're going to have to find some better explanations.

I think the biggest problem is that it's taking natural human variation and claiming there's a selection for it, rather than recognising that there's natural human variation and some sports are better suited to subsets of that variation. There's a reason you don't see many dumpy, big-breasted women on the professional marathon circuit but that doesn't mean that we've all been sexually selected for not running far. Oh, I can see it now - women who are dumpy and big-breasted are sexually selected because their big boobs mean they can produce more milk, therefore raising healthier kids, and their dumpiness means they're less likely to run away from bad partners or be at risk of cuckolding due to their unattractiveness. Give me a chance to slap in a couple of references and I'm sure I can come up with something publishable.

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Re: Is arm length sexually selected?

Post by Martin Y » Wed Nov 04, 2020 2:04 pm

Have they considered the evolutionary benefit of seeking a partner who can get stuff down from high shelves?

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Re: Is arm length sexually selected?

Post by Bird on a Fire » Wed Nov 04, 2020 2:38 pm

There's two parts to their hypothesis, which shouldn't be conflated. They're not saying that because martial arts exist women are attracted to violence.

1. Arm length is sexually dimorphic, i.e. if you take men and women of the same height, men will tend to have longer arms than women. This seems simple enough to confirm with measurements that I assume it's uncontroversial.

2. Longer arms are useful in a fight. This is where the sports comes in - martial arts provides a convenient sample of people who consent to being in fights. The authors correlate their arm length with their success.

They find a weak but positive relationship between arm length and success, which supports the second part of the hypothesis. Obviously martial artists aren't a random sample of the population, but there are probably ethical issues with getting random people to fight each other. I'd expect that longer arms are actually more useful outside of martial arts, where technique is less of a factor than sheer size.

I don't think it's particularly controversial to suggest that men sometimes use violence to get stuff they want. They provide several references in the first paragraph of the article:
Growing evidence suggests that human males have been intrasexually selected for violent contest competition (Hill, Bailey, & Puts, 2017; Puts, 2010), and may possess adaptations specifically for fighting (Carrier, 2011; Carrier & Morgan, 2015; Třebický, Stirrat, & Havlíček, 2019).
If longer arms help males to win at violence they'd probably be selected for if there are no great costs.


As for what it says about women's preferences, selection doesn't require that 100% of copulations derive from a particular trait, only that the trait gives an incremental advantage in evolutionary time. For example, even if non-consensual copulation was rare, being successful at it might provide an evolutionary advantage - again if there are no great costs, like social opprobrium, but at least in modern times men who control a lot of resources seem to be able to get away with treating women terribly.

From what I remember of behavioural ecology lectures as an undergrad there is quite a bit of evidence that, all things being equal, men who control a lot of resources have more kids, in both modern and traditional societies.

Fishnut wrote:
Wed Nov 04, 2020 1:20 pm
I think the biggest problem is that it's taking natural human variation and claiming there's a selection for it, rather than recognising that there's natural human variation and some sports are better suited to subsets of that variation. There's a reason you don't see many dumpy, big-breasted women on the professional marathon circuit but that doesn't mean that we've all been sexually selected for not running far. Oh, I can see it now - women who are dumpy and big-breasted are sexually selected because their big boobs mean they can produce more milk, therefore raising healthier kids, and their dumpiness means they're less likely to run away from bad partners or be at risk of cuckolding due to their unattractiveness. Give me a chance to slap in a couple of references and I'm sure I can come up with something publishable.
I know you're joking, but in the interest of taking-the-joke-too-seriously here are some critiques *dons Reviewer #2 hat*.
- Evolutionary theory generally suggests that the selection on females is to select good partners. In that context, running away from bad partners should be selected for, not against.
- I don't think breast size is correlated with milk production, but it is correlated with fertility (within individuals at least).
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Re: Is arm length sexually selected?

Post by Martin Y » Wed Nov 04, 2020 3:30 pm

Bird on a Fire wrote:
Wed Nov 04, 2020 2:38 pm
... If longer arms help males to win at violence they'd probably be selected for if there are no great costs.


As for what it says about women's preferences, selection doesn't require that 100% of copulations derive from a particular trait, only that the trait gives an incremental advantage in evolutionary time.
Indeed. If having longer arms helps men win fights against other men then that sounds like it would convey a survival advantage, not so much being able to kill the other guy rather than being killed but gaining status within a band and getting your pick of the food, that sort of thing. So it could be selected for without women preferring the trait itself.

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Re: Is arm length sexually selected?

Post by jimbob » Wed Nov 04, 2020 3:38 pm

Bird on a Fire wrote:
Wed Nov 04, 2020 2:38 pm

2. Longer arms are useful in a fight. This is where the sports comes in - martial arts provides a convenient sample of people who consent to being in fights. The authors correlate their arm length with their success.

They find a weak but positive relationship between arm length and success, which supports the second part of the hypothesis. Obviously martial artists aren't a random sample of the population, but there are probably ethical issues with getting random people to fight each other. I'd expect that longer arms are actually more useful outside of martial arts, where technique is less of a factor than sheer size.
There is a bigger problem. Chimps will use sticks at least to threaten their peers. Hominids have been using tools probably since our ancestors split from those of chimps.

So unarmed fighting is probably a minor thing, compared to the hitting/clubbing/stabbing/beating with a pointy or blunt stick.

I can believe that arm length would still be an advantage, but weapons do tend to equalise things.
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Re: Is arm length sexually selected?

Post by Martin Y » Wed Nov 04, 2020 3:56 pm

Doubt if I can find it now but I'm sure there's at least one Lindybeige vid on YouTube where he notes what seems to be the benefit of a longer reach while enthusiastic reenactors* bash each other around with plastic swords and spears.

*That'll be the wrong term. I mean people who want to practically study old fighting techniques, not dress up like living history.

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Re: Is arm length sexually selected?

Post by Bird on a Fire » Wed Nov 04, 2020 4:02 pm

Tool use is a factor in an actual fight, yes, especially if you're trying to actually injure or kill someone.

But a lot of the time, verbal aggression escalates into physical aggression without premeditation - think of drunk blokes pushing and shoving each other, and maybe throwing a fist. Those gentle scuffles probably give plenty of information about who's likely to win in a fight, in the way that loads of other mammals use things like roaring and showing teeth and beating chests and a bit of biting and scratching to - counterintuitively, perhaps - reduce the risk of serious violence.

If we're scrapping over the last mammoth rib or whatever, the longer-armed bloke might do better most of the time, even if in a true life-or-death situation the pointy-stick bloke would have the upper hand.
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Re: Is arm length sexually selected?

Post by dyqik » Wed Nov 04, 2020 6:38 pm

Bird on a Fire wrote:
Wed Nov 04, 2020 4:02 pm
If we're scrapping over the last mammoth rib or whatever, the longer-armed bloke might do better most of the time, even if in a true life-or-death situation the pointy-stick bloke would have the upper hand.
But does "doing better most of the time in a non-life-or-death situation" actually help select for arm length enough to have an effect?

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Re: Is arm length sexually selected?

Post by Bird on a Fire » Wed Nov 04, 2020 6:45 pm

dyqik wrote:
Wed Nov 04, 2020 6:38 pm
Bird on a Fire wrote:
Wed Nov 04, 2020 4:02 pm
If we're scrapping over the last mammoth rib or whatever, the longer-armed bloke might do better most of the time, even if in a true life-or-death situation the pointy-stick bloke would have the upper hand.
But does "doing better most of the time in a non-life-or-death situation" actually help select for arm length enough to have an effect?
It's certainly a widespread assumption in studies of evolutionary adaptation across the board.

I think probably yes, once you remember that these processes are probabilistic and occurring over geological time. A bit better fed means a bit more likely to survive harsh weather, a bit more power means you get to shag a bit more, etc.

There certainly are critiques of this kind of adaptationist paradigm that have been made for a long, long time, but what issues exist are by no means limited to studies of human sexual selection. There's a bazillion bird papers, for instance, observing that some trait helps get food in some way, and then hypothesising that it would therefore be selected for. I don't think it's an unreasonable assumption, tbh, though for obvious reasons not easy to demonstrate empirically.
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Re: Is arm length sexually selected?

Post by bjn » Wed Nov 04, 2020 8:18 pm

Martin Y wrote:
Wed Nov 04, 2020 3:56 pm
Doubt if I can find it now but I'm sure there's at least one Lindybeige vid on YouTube where he notes what seems to be the benefit of a longer reach while enthusiastic reenactors* bash each other around with plastic swords and spears.

*That'll be the wrong term. I mean people who want to practically study old fighting techniques, not dress up like living history.
You called?

HEMA, historical european martial arts. Like what I research and teach as a hobby. And Lindy has some umm, interesting takes on things.

The longer your weapon, the better chance you have of striking your opponent before they can come into their range. However, the longer your weapon, the more of a pain it is to carry around, and if you don’t get the strike in first, your opponent has a good chance of getting to you and counter attacking. eg: spear person misses or has their attack put aside, their sword wielding opponent gets inside their range and the spear carrier is fecked.

This holds for longer arms in unarmed combat. Punching some one out with one or two hits is a highly trained skill that has a good chance of breaking your hand in the process*. Longer arms will help you get in first, but not that much, you’ve got to be relatively close to land a decent blow using hips and shoulders, while using your arms to fend off your opponents strike.

However, grappling is what hurts, not punching. In a fight for survival, I want to be in close using my hands and knees to do horrible things to your eyes, throat, genitals etc... while trying to throw you to the ground to have you at my mercy for even more. Long arms don’t help there, strength and speed does. I’d take a few slaps around the head to get into grappling range. I’ll even grab your arms as you strike at me to control the fight and use that as an opening to come the close. I really don’t see a huge advantage to longer arms in any fight that doesn’t stick to puglism rules. Look at modern MMA to see what happens.

*case in point, one of my HEMA club fellow instructors used to be a teen MMA champ. Some fools tried to mug him on the way home one night, he knocked them both out in a second when the reflexes kicked in. But he had years of training to hone those skills, not sure if our early evolutionary ancestors attended boxing classes. He also broke both hands, which would not be a huge evolutionary advantage.

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Re: Is arm length sexually selected?

Post by Martin Y » Wed Nov 04, 2020 8:48 pm

bjn wrote:
Wed Nov 04, 2020 8:18 pm
You called?
Even as I typed I had the sense I was laying a snare.
... Lindy has some umm, interesting takes on things.
You are not the first with an actual expertise who thinks that about him. Tells a great story with confidence but possibly a bit more wot-I-reckon than thoroughly factual.
<snip> I really don’t see a huge advantage to longer arms in any fight that doesn’t stick to puglism rules.
Interesting. Ta.

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Re: Is arm length sexually selected?

Post by jimbob » Wed Nov 04, 2020 9:43 pm

Bird on a Fire wrote:
Wed Nov 04, 2020 4:02 pm
Tool use is a factor in an actual fight, yes, especially if you're trying to actually injure or kill someone.

But a lot of the time, verbal aggression escalates into physical aggression without premeditation - think of drunk blokes pushing and shoving each other, and maybe throwing a fist. Those gentle scuffles probably give plenty of information about who's likely to win in a fight, in the way that loads of other mammals use things like roaring and showing teeth and beating chests and a bit of biting and scratching to - counterintuitively, perhaps - reduce the risk of serious violence.

If we're scrapping over the last mammoth rib or whatever, the longer-armed bloke might do better most of the time, even if in a true life-or-death situation the pointy-stick bloke would have the upper hand.
I was also thinking that if you are in such a society, cooperation is important - as it is in chimps. You're not going to do very well in the *next* hunt if you've got a reputation for being a bully when everyone is unarmed. I'm sure in such situations, you'd end up having unfortunate accidents, or finding that even the next time you're all unarmed, that a group of others have ganged up on you.

And I was wondering about invoking BJN
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Re: Is arm length sexually selected?

Post by Bird on a Fire » Thu Nov 05, 2020 8:27 am

This might be of interest https://en.m.wikipedia.org/wiki/Sexual_ ... n_primates

So, what are some alternative explanations for sexual dimorphism in arm length in humans? If not for fighting each other... Hunting?
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Re: Is arm length sexually selected?

Post by secret squirrel » Thu Nov 05, 2020 9:33 am

bjn wrote:
Wed Nov 04, 2020 8:18 pm
Martin Y wrote:
Wed Nov 04, 2020 3:56 pm
Doubt if I can find it now but I'm sure there's at least one Lindybeige vid on YouTube where he notes what seems to be the benefit of a longer reach while enthusiastic reenactors* bash each other around with plastic swords and spears.

*That'll be the wrong term. I mean people who want to practically study old fighting techniques, not dress up like living history.
You called?

HEMA, historical european martial arts. Like what I research and teach as a hobby. And Lindy has some umm, interesting takes on things.

The longer your weapon, the better chance you have of striking your opponent before they can come into their range. However, the longer your weapon, the more of a pain it is to carry around, and if you don’t get the strike in first, your opponent has a good chance of getting to you and counter attacking. eg: spear person misses or has their attack put aside, their sword wielding opponent gets inside their range and the spear carrier is fecked.

This holds for longer arms in unarmed combat. Punching some one out with one or two hits is a highly trained skill that has a good chance of breaking your hand in the process*. Longer arms will help you get in first, but not that much, you’ve got to be relatively close to land a decent blow using hips and shoulders, while using your arms to fend off your opponents strike.

However, grappling is what hurts, not punching. In a fight for survival, I want to be in close using my hands and knees to do horrible things to your eyes, throat, genitals etc... while trying to throw you to the ground to have you at my mercy for even more. Long arms don’t help there, strength and speed does. I’d take a few slaps around the head to get into grappling range. I’ll even grab your arms as you strike at me to control the fight and use that as an opening to come the close. I really don’t see a huge advantage to longer arms in any fight that doesn’t stick to puglism rules. Look at modern MMA to see what happens.

*case in point, one of my HEMA club fellow instructors used to be a teen MMA champ. Some fools tried to mug him on the way home one night, he knocked them both out in a second when the reflexes kicked in. But he had years of training to hone those skills, not sure if our early evolutionary ancestors attended boxing classes. He also broke both hands, which would not be a huge evolutionary advantage.
Yes, striking as it occurs in MMA/boxing etc. is quite artificial. Even in MMA the rules are set up to discourage grappling (short rounds, stand-ups for inaction etc.), and of course gloves benefit strikers a lot. Most people don't actually punch well enough to do much damage to each other, so winning fights is much more about size and aggression than anything else. Really not convinced we can extrapolate evolutionary advantages from combat sports as the article suggests.

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Re: Is arm length sexually selected?

Post by jimbob » Thu Nov 05, 2020 10:50 am

secret squirrel wrote:
Thu Nov 05, 2020 9:33 am
bjn wrote:
Wed Nov 04, 2020 8:18 pm
Martin Y wrote:
Wed Nov 04, 2020 3:56 pm
Doubt if I can find it now but I'm sure there's at least one Lindybeige vid on YouTube where he notes what seems to be the benefit of a longer reach while enthusiastic reenactors* bash each other around with plastic swords and spears.

*That'll be the wrong term. I mean people who want to practically study old fighting techniques, not dress up like living history.
You called?

HEMA, historical european martial arts. Like what I research and teach as a hobby. And Lindy has some umm, interesting takes on things.

The longer your weapon, the better chance you have of striking your opponent before they can come into their range. However, the longer your weapon, the more of a pain it is to carry around, and if you don’t get the strike in first, your opponent has a good chance of getting to you and counter attacking. eg: spear person misses or has their attack put aside, their sword wielding opponent gets inside their range and the spear carrier is fecked.

This holds for longer arms in unarmed combat. Punching some one out with one or two hits is a highly trained skill that has a good chance of breaking your hand in the process*. Longer arms will help you get in first, but not that much, you’ve got to be relatively close to land a decent blow using hips and shoulders, while using your arms to fend off your opponents strike.

However, grappling is what hurts, not punching. In a fight for survival, I want to be in close using my hands and knees to do horrible things to your eyes, throat, genitals etc... while trying to throw you to the ground to have you at my mercy for even more. Long arms don’t help there, strength and speed does. I’d take a few slaps around the head to get into grappling range. I’ll even grab your arms as you strike at me to control the fight and use that as an opening to come the close. I really don’t see a huge advantage to longer arms in any fight that doesn’t stick to puglism rules. Look at modern MMA to see what happens.

*case in point, one of my HEMA club fellow instructors used to be a teen MMA champ. Some fools tried to mug him on the way home one night, he knocked them both out in a second when the reflexes kicked in. But he had years of training to hone those skills, not sure if our early evolutionary ancestors attended boxing classes. He also broke both hands, which would not be a huge evolutionary advantage.
Yes, striking as it occurs in MMA/boxing etc. is quite artificial. Even in MMA the rules are set up to discourage grappling (short rounds, stand-ups for inaction etc.), and of course gloves benefit strikers a lot. Most people don't actually punch well enough to do much damage to each other, so winning fights is much more about size and aggression than anything else. Really not convinced we can extrapolate evolutionary advantages from combat sports as the article suggests.
In this context, the book "Chimpanzee Politics" is interesting. The alpha male is not necessarily the strongest male. Frans de Waal describes one occasion where an upcoming male deposed the previous alpha male who then started grooming a teenage gamma male, and together they deposed (and killed) the previous one - who was still stronger than either.

Lots of discussions about alliances and approaches* to leadership by the chimps.

*The book makes a good case that this is an appropriate description and not anthropomorphism
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Re: Is arm length sexually selected?

Post by bob sterman » Thu Nov 05, 2020 10:51 am

Hominid males (much more often than Hominid females) have likely be striking each other with rocks, logs, and more sophisticated axe-like tools for more than 1 million years.

Whether arm length contributes to success in that sort of combat is much more relevant.

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Re: Is arm length sexually selected?

Post by jimbob » Thu Nov 05, 2020 1:46 pm

bob sterman wrote:
Thu Nov 05, 2020 10:51 am
Hominid males (much more often than Hominid females) have likely be striking each other with rocks, logs, and more sophisticated axe-like tools for more than 1 million years.

Whether arm length contributes to success in that sort of combat is much more relevant.
Exactly. Just like us, our ancestors were obligate tool users, and need a society to actually survive even then.

Meanwhile, I just got this link to a nice article in Science:

https://advances.sciencemag.org/content/6/45/eabd0310
Abstract
Sexual division of labor with females as gatherers and males as hunters is a major empirical regularity of hunter-gatherer ethnography, suggesting an ancestral behavioral pattern. We present an archeological discovery and meta-analysis that challenge the man-the-hunter hypothesis. Excavations at the Andean highland site of Wilamaya Patjxa reveal a 9000-year-old human burial (WMP6) associated with a hunting toolkit of stone projectile points and animal processing tools. Osteological, proteomic, and isotopic analyses indicate that this early hunter was a young adult female who subsisted on terrestrial plants and animals. Analysis of Late Pleistocene and Early Holocene burial practices throughout the Americas situate WMP6 as the earliest and most secure hunter burial in a sample that includes 10 other females in statistical parity with early male hunter burials. The findings are consistent with nongendered labor practices in which early hunter-gatherer females were big-game hunters.
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Re: Is arm length sexually selected?

Post by Martin Y » Thu Nov 05, 2020 3:13 pm

So it is just getting things from high shelves after all.

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Re: Is arm length sexually selected?

Post by shpalman » Thu Nov 05, 2020 5:35 pm

Bear in mind that a hereditable trait doesn't really have to be useful anymore for it to be selected for - maybe at some point in the past it was useful so partners who noticed it and liked it went on to have more successful offspring, but now partners just notice it and like it so their offspring will have the same trait and so be noticed and liked by more prospective partners in the next generation.

tl;dr organisms choose attractive mates so that their offspring will be attractive, for completely arbitrary definitions of "attractive" as long as everyone* agrees on the same ones.

The other thing I remember is that thing from a few years ago about male faces evolving to be punchable, or something.
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Re: Is arm length sexually selected?

Post by jimbob » Thu Nov 05, 2020 6:24 pm

shpalman wrote:
Thu Nov 05, 2020 5:35 pm
Bear in mind that a hereditable trait doesn't really have to be useful anymore for it to be selected for - maybe at some point in the past it was useful so partners who noticed it and liked it went on to have more successful offspring, but now partners just notice it and like it so their offspring will have the same trait and so be noticed and liked by more prospective partners in the next generation.

tl;dr organisms choose attractive mates so that their offspring will be attractive, for completely arbitrary definitions of "attractive" as long as everyone* agrees on the same ones.

The other thing I remember is that thing from a few years ago about male faces evolving to be punchable, or something.
Michael Gove as the pinnacle of that evolution
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Re: Is arm length sexually selected?

Post by sTeamTraen » Thu Nov 05, 2020 8:59 pm

Surely larger *anything* is typically going to be correlated with reproductive success (fnarr), except if it gets to the point where the additional intertia it gets to be a handicap? I would expect the number of phenotypes where smaller is fitter to be far smaller than those where larger is better, simply because distributions are bounded at zero at the lower end.

(Mind you, I am not very good at statistics and I have had a couple of glasses of wine while taking an absurd interest in the minutiae of a few piles of slips of paper in various parts of the US&A that I can't always place on the map first time. But I think this is sounds like something that Stephen Jay Gould could have come up with, so ner.)
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Re: Is arm length sexually selected?

Post by Bird on a Fire » Thu Nov 05, 2020 9:08 pm

Well, specifically we're looking for an explanation of why men have disproportionately longer arms than women, after taking general size into account. It's not just "bigger is better" but "bigger is better especially for males". So the explanation should encompass why the cost-benefit analysis is different for men and women.

That's probably going to mean something that either females do disproportionately e.g. childbearing and rearing, or something that males do disproportionately, like fighting or hunting.
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Re: Is arm length sexually selected?

Post by jimbob » Thu Nov 05, 2020 9:15 pm

Bird on a Fire wrote:
Thu Nov 05, 2020 9:08 pm

That's probably going to mean something that either females do disproportionately e.g. childbearing and rearing, or something that males do disproportionately, like fighting or hunting.
Or not
jimbob wrote:
Thu Nov 05, 2020 1:46 pm


Meanwhile, I just got this link to a nice article in Science:

https://advances.sciencemag.org/content/6/45/eabd0310
Abstract
Sexual division of labor with females as gatherers and males as hunters is a major empirical regularity of hunter-gatherer ethnography, suggesting an ancestral behavioral pattern. We present an archeological discovery and meta-analysis that challenge the man-the-hunter hypothesis. Excavations at the Andean highland site of Wilamaya Patjxa reveal a 9000-year-old human burial (WMP6) associated with a hunting toolkit of stone projectile points and animal processing tools. Osteological, proteomic, and isotopic analyses indicate that this early hunter was a young adult female who subsisted on terrestrial plants and animals. Analysis of Late Pleistocene and Early Holocene burial practices throughout the Americas situate WMP6 as the earliest and most secure hunter burial in a sample that includes 10 other females in statistical parity with early male hunter burials. The findings are consistent with nongendered labor practices in which early hunter-gatherer females were big-game hunters.
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Re: Is arm length sexually selected?

Post by Bird on a Fire » Thu Nov 05, 2020 9:32 pm

Did you mean to cross out hunting rather than fighting, there?

That's an interesting article, though, sorry for not acknowledging it. OTOH, I have no idea what the relevant timeframe for body-size evolution would be, but I strongly suspect it's a lot longer than 9000 years. Very tricky to get cultural information about the distant past, of course.
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Re: Is arm length sexually selected?

Post by jimbob » Thu Nov 05, 2020 9:54 pm

Bird on a Fire wrote:
Thu Nov 05, 2020 9:32 pm
Did you mean to cross out hunting rather than fighting, there?

That's an interesting article, though, sorry for not acknowledging it. OTOH, I have no idea what the relevant timeframe for body-size evolution would be, but I strongly suspect it's a lot longer than 9000 years. Very tricky to get cultural information about the distant past, of course.
True... but we know that adolescent female chimps are the ones who have innovated spears for hunting bushbabies, so I don't think there's any reason to think it's not been common amongst our ancestors.

I guess it makes sense, if you're a teenager and not yet pregnant, in many situations, you could have a better chance of increasing your family's protein sources if you helped in hunting.
Have you considered stupidity as an explanation

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