The didn't decide, they observed; consistent directional pressure over thousands of years is strong evidence that an allele is being selected for.
Well that's a given mate, nobody's talking about populations that dont reproduce are they? And even then you're still making the same tautological mistake.... If they survived they must have been fit
That is, traits that stop registering may no longer be something that helps survival. But that does not mean they were not necessary for survival at an earlier point.
Several examples from the paper are exactly that. E.g dark skin was better for survival in Africa, but as populations moved north light skin was strongly selected for. Given the levels of sunlight in Europe, lighter skin increased fitness.
That is, it is not an argument against any of the traits that are present. Is why I said the problem is with how it was stated. But you do not have everything with you to provide evidence for all of the things necessary for you to have gotten here. At best, you have evidence that nothing you have with you prevented you from getting here.
That make sense? I grant that pulling it back up, I see the comment I was responding to was hedged. My concern is largely against the idea that things that "were selected for" in the past can be determined by evidence. I'm not convinced it can't be. But I find this presentation of it to be somewhat weak.
They aren't saying "we see these things now, so they must be good" but rather things like "we see these selected for from 9kya to 3kya, but from then to the present they were selected against"; they are specifically looking at how apparent selective pressures changed over time.
> the idea that things that "were selected for" in the past can be determined by evidence
When the evidence is a copious selection of ancient genomes, distributed over both space and time, they certainly can be.
The callout on "evidence" I have there is that I meant that to only be present evidence. And again, I am not convinced it can't be done. It takes a lot of work. Which, the article is doing. But just saying that traits that helped you survive are typically retained, so by definition increase fitness, does not.
It's like holding a large ball in place on a hill that sees frequent tremors. If the ball is still halfway up the hill it's being held in place, if it's being held in place it's still halfway up the hill. It might be considered a tautology if you're only working with symbols and ignore all the mechanistics.
"degraded"? Aren't random mutations precisely one of the core mechanism of adaptation?
Remember, all improvements are changes, but most changes aren't improvements. The trick that makes evolution works is this: out of lots of random changes, most of which are harmful, the harmful ones tend to be weeded out and the useful ones tend to spread.
- lactose tolerance
- immunity and disease resistance
- lighter skin at northern latitudes
- metabolism and vitamin D processing changes in response to changes in diet after the rise of agriculture
Wrong. Fitness is not "beyond" increasing the odds of survival, fitness is ONLY that. Fitness is not about quality of life.
- in that ecosystem they are inhabiting, be more healthy than those who don't.
Survival of the fittest says nothing about how healthy they are, only whether they survive and reproduce or not.
So it should really be "If it survives it must have been fit"