[VoodooJuJu]

>95,000 years is plenty of time for adaptations in diet

Is it? Is it enough for all kinds of dietary adaptations? If me and my progeny eat grass for 95,000 years, will we adapt to be able to digest it?

On lactose: many of us carry the mutation that helps us digest lactose into adulthood (without any seeming issues). But does that make it ideal to consume? Is consumption of lactose into adulthood causing any issues that I can't readily detect?

[twobitshifter]

Yes if you eat grass and somehow survive to procreate you will have adapted to be able to digest it and sustain your species. Of course if you lack the genes you’ll die off and if the whole species lacks any genes and all that’s left to eat is grass, we all die. I believe from studying skeletons we know that agriculture first led to a decline in physical fitness and overall health - evidence that we weren’t well adapted at that time.

[hnthrowaway8493]

That's not how evolution works. The question to ask is, if most food sources except for grass disappeared, would humanity as a whole (through mass starvation and the resulting natural selection) adapt to be able to survive on grass within the next 95000 years? And the answer isn't necessarily yes; humans might also just go extinct.