[lurquer]

> There is no disadvantage to being able to synthesise vitamin C, and no advantage in dropping the trait.

So why did the trait of that mutant primate spread throughout the entire population? There should instead be a mixture of those who can and those who can’t synthesize vitamin C.

(Indeed, one should perhaps not so blithely assume that there was sufficient fruit for everyone and so C didn’t matter… for it is precisely the ability to survive in times of drought and scarcity that drive evolution, and there id no reason to suspect a population that could synthesize their own vitamin C was less fit than a population that couldn’t. The issue of vitamin C is far from simple…)

[arp242]

There is no reason for it to spread, but also no reason for it not to. Presumably there was another (completely unrelated) trait, and it happened to spread because of that.

> There should instead be a mixture of those who can and those who can’t synthesize vitamin C.

Probably was for a long time. All of this happened about 60 millions years ago. It's been a while.

[shellfishgene]

It's more likely that a mutation in the gene/pathway arose multiple times independently, instead of one spreading through the population.