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How about chicks dig guys with a manly chin. Don't know how you can call yourself an evolutionary biologist if you so easily overlook sexual selection.

wodenokoto 12y ago
Because you need to ask why they dig a manly chin. Long hair makes sense because it is a crude history of our health. Symmetry also makes sense, as it is a sign of healthy, strong genes. Being rich enough to afford to waste stuff also makes sense (and explain a ton of weird human and animal behavior) But if a chin serves no purpose what so ever, why would it become a sex symbol? They're not big enough to work like antlers (look how much energy I can accrue to grow these big ass antlers!) so why would they start to grow in the first place?
- keithwhor 12y ago
  Having a large / strong jaw and chin is correlated with higher testosterone levels and is a secondary sexual characteristic in males. Higher testosterone levels are correlated with a weakened immune response. So yes, a "manly chin" may very well have been selected for on the basis of showing the strength of the individual by artificially handicapping them (being genetically "rich enough" as you put it). Interestingly, beards act to further emphasize the chin. And we're one of the few animals to have those, too.
- whoopdedo 12y ago
  It is unclear whether sexual selection impedes or facilitates natural selection [1]. Sexual selection can happen just because. A female who prefers chins will give birth to sons with chins and daughters who like chins. It's a positive feedback loop that doesn't need cooperation from natural selection to give it fitness. At one time in the past there may have been a reason that the men with chins were more successful than other humans. The correlation may have been coincidental though. Maybe the men with no-chins happened to be living in a part of the world that suffered a famine. Or if there was a direct relationship, the sexual preference remained after the natural advantage was no longer relevant. The study does a good eliminating mechanical advantage as a reason for having a jaw. (And that's all it says.) But the speculation about why the jaw exists (inserted by the news writer and has nothing to do with this study) seems less certain to me. Why did chins not simply get smaller with the rest of the skull? Something encouraged chin growth in humans. But to say what you'd have to study skulls from the past to see exactly how the chin changed over time. [1] http://www.cell.com/current-biology/abstract/S0960-9822%2811%2901397-2 http://www.cell.com/current-biology/abstract/S0960-9822%2811...

wodenokoto 12y ago

Because you need to ask why they dig a manly chin. Long hair makes sense because it is a crude history of our health. Symmetry also makes sense, as it is a sign of healthy, strong genes. Being rich enough to afford to waste stuff also makes sense (and explain a ton of weird human and animal behavior) But if a chin serves no purpose what so ever, why would it become a sex symbol? They're not big enough to work like antlers (look how much energy I can accrue to grow these big ass antlers!) so why would they start to grow in the first place?

keithwhor 12y ago
Having a large / strong jaw and chin is correlated with higher testosterone levels and is a secondary sexual characteristic in males. Higher testosterone levels are correlated with a weakened immune response. So yes, a "manly chin" may very well have been selected for on the basis of showing the strength of the individual by artificially handicapping them (being genetically "rich enough" as you put it). Interestingly, beards act to further emphasize the chin. And we're one of the few animals to have those, too.
whoopdedo 12y ago
It is unclear whether sexual selection impedes or facilitates natural selection [1]. Sexual selection can happen just because. A female who prefers chins will give birth to sons with chins and daughters who like chins. It's a positive feedback loop that doesn't need cooperation from natural selection to give it fitness. At one time in the past there may have been a reason that the men with chins were more successful than other humans. The correlation may have been coincidental though. Maybe the men with no-chins happened to be living in a part of the world that suffered a famine. Or if there was a direct relationship, the sexual preference remained after the natural advantage was no longer relevant. The study does a good eliminating mechanical advantage as a reason for having a jaw. (And that's all it says.) But the speculation about why the jaw exists (inserted by the news writer and has nothing to do with this study) seems less certain to me. Why did chins not simply get smaller with the rest of the skull? Something encouraged chin growth in humans. But to say what you'd have to study skulls from the past to see exactly how the chin changed over time. [1] http://www.cell.com/current-biology/abstract/S0960-9822%2811%2901397-2 http://www.cell.com/current-biology/abstract/S0960-9822%2811...