It is unclear whether sexual selection impedes or facilitates natural selection [1]. Sexual selection can happen just because. A female who prefers chins will g

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...