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> Specifically, if it were true, we would see all sorts of genetic correlations where one good trait systematically boosts a bad trait. And what if it's true f

by maratd 9y ago

> Specifically, if it were true, we would see all sorts of genetic correlations where one good trait systematically boosts a bad trait. And what if it's true for a short period of time until a new mutation arises that eliminates the double edged sword? Most of our adaptations are really really old. They've had enough time to "perfect" themselves. What if evolution isn't clean or pretty? What if it's a messy business where a gene arises that gives a small edge, but brings with it a host of problems. It'll still spread because of that edge and it may take millions of years to sort out and eliminate the side-effects.

gwern 9y ago
> What if it's a messy business where a gene arises that gives a small edge, but brings with it a host of problems. Because it doesn't. That sort of pleiotropy just is not common, empirically, in humans. Hundreds or thousands of genetic correlations tend to confirm this: there are loads of free lunches. Why is that? A lot of it looks like relaxed selection (eg my other submission shows that our ancestors thousands of years ago appear to have had substantially lower genetic risk of disease because it was decreasing over time, but has reversed), the slowness of selection given the small effect sizes vs the constant incoming stream of new mutations, and the demographic history of humanity of massive expansion from a small starting population based on migration of also tiny groups.
- narag 9y ago
  our ancestors thousands of years ago appear to have had substantially lower genetic risk of disease If I understood you correctly, environment pressure relaxed for former traits. But then the new human environment caused the presure for other set of mutations to kick in, even if they're counterproductive for old environment...
Obi_Juan_Kenobi 9y ago
Selection is performed at the level of populations, where there must be a net fitness benefit for positive selection. For your messy argument to work, there must be a change in the evolutionary context such that a trait that was once favored loses it fitness benefit, and instead any detrimental effects that were 'carried along' are now on display. There really is no 'hiding' in evolution; if a trait has deleterious effects, even only in specific genetic or environmental contexts, then they are felt. It is this brutally simple force that permits such complex systems to function effectively.

by maratd 9y ago

gwern 9y ago

> What if it's a messy business where a gene arises that gives a small edge, but brings with it a host of problems. Because it doesn't. That sort of pleiotropy just is not common, empirically, in humans. Hundreds or thousands of genetic correlations tend to confirm this: there are loads of free lunches. Why is that? A lot of it looks like relaxed selection (eg my other submission shows that our ancestors thousands of years ago appear to have had substantially lower genetic risk of disease because it was decreasing over time, but has reversed), the slowness of selection given the small effect sizes vs the constant incoming stream of new mutations, and the demographic history of humanity of massive expansion from a small starting population based on migration of also tiny groups.

narag 9y ago
our ancestors thousands of years ago appear to have had substantially lower genetic risk of disease If I understood you correctly, environment pressure relaxed for former traits. But then the new human environment caused the presure for other set of mutations to kick in, even if they're counterproductive for old environment...

Obi_Juan_Kenobi 9y ago

Selection is performed at the level of populations, where there must be a net fitness benefit for positive selection. For your messy argument to work, there must be a change in the evolutionary context such that a trait that was once favored loses it fitness benefit, and instead any detrimental effects that were 'carried along' are now on display. There really is no 'hiding' in evolution; if a trait has deleterious effects, even only in specific genetic or environmental contexts, then they are felt. It is this brutally simple force that permits such complex systems to function effectively.