- 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"
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.
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.