It's tough to use intuition to bring any real insight to bear on biological systems, I'd be really interested in finding some real research into the matter.
Re: the lifejackets I was demonstrating that the effectiveness of the jackets is not effected by who chooses to use them. I was pointing out that saying less intelligent people gravitate towards sprinting does not prove that sprinting has no positive benefits on intelligence.
Re: the lifejackets I was demonstrating that the effectiveness of the jackets is not effected by who chooses to use them. I was pointing out that saying less intelligent people gravitate towards sprinting does not prove that sprinting has no positive benefits on intelligence.