Yep, rates of evolution (in particular mutation rate and drift) are proportional to population size, and we have a larger population size than we ever have in the past.
~2 billion base pairs * ~1 in a billion error rate = 2 mutations per generation (on average)
Edit: Slight clarification and a brief (and greatly oversimplified) lesson on how this works.
Let Ne = effective population size. And I'll define "fitness effect" as the advantage conferred by a particular mutation in a particular fitness landscape. e.g., If you're an E. coli, the fitness conferred by penicillin resistance is very high if you're sitting in a pool of penicillin, but generally mildly negative otherwise because you're wasting energy.
When the fitness effect size is much larger in magnitude than 1/Ne (or 1/2Ne if you're diploid, like us), the fate of the gene is largely determined by natural selection. (But add the occasional coin toss in there b/c the real world is messy.)
When the fitness effect size is much smaller in magnitude than 1/Ne, the fate of the gene is largely determined by genetic drift. https://en.wikipedia.org/wiki/Genetic_drift (tl;dr Mostly chance mod a few other effects, like if the mutation of interest has a physical location close to another mutation with strong selection pressure)
However, there are slightly deleterious or slightly advantageous mutations, whose fitness effect size is close to 1/Ne (or 1/2Ne for diploids), and things get kinda interesting, because it's a combination of genetic drift and natural selection. For instance, if it's a slightly deleterious mutation, it will decrease Ne slightly (increasing the proportion of mutations that are considered neutral of the new value of Ne), and the previously "slightly deleterious" mutation may now be effectively neutral for the new value of Ne.
There is a lot of evidence that the "slightly" deleterious and the "slightly" advantageous mutations contribute substantially to evolutionary dynamics.
This is further complicated by the fact that the fitness (whether a mutation is deleterious or advantageous) is not constant everywhere geographically, or over time.
Speed of evolution depends on how strongly the adaptation influences reproductive success. It's possible that grain causes subtle long-term damage that mostly kills people past reproductive age, whereas lactose tolerance is of immediate benefit. If this is true then grain tolerance would evolve much slower than lactose tolerance. But note that the "subtle long term" damage argument applies to all foods, and it's uncertain if grains are significantly worse than any other.
> It's possible that grain causes subtle long-term damage that mostly kills people past reproductive age, whereas lactose tolerance is of immediate benefit.
Sure, and it's also possible the human body has already adapted to processing grains without long term damage, and it's possible that there was never any damage by consuming grains in the first place (the body is highly adaptable). All this line of argument is stating is that without any information, we have no information.
What Retric was stating is different though. There exists digestive adaptations that have happened relatively rapidly in relatively recent history, therefore merely the fact that foods were not available in more ancient history is not sufficient to argue that they "aren't good" for the body.
And, as many gluten-sensitive (but not allergic) people told in a recent thread on reddit, where the topic came up, they have next to no issue with the hand-baked bread you find in small bakeries in Europe, but the issues often only show when eating mass-produced bread.
It’s more likely that gluten sensitivity is just caused by a cross-interaction with an additive used for bleaching or similar.
Aren't lactose tolerances wildly different between populations? With e.g. Northern European ancestry people having very high lactose tolerance and East Asian ancestry people having much lower lactose tolerance?
