Obesity among US adults has gone from 10-15% in the 60s to 40% now. It's extremely unlikely that genetics changed in 60 years, but environmentals did.
I understand that some have genetics that make it harder for them to keep off weight, either by metabolism, neural hunger stimuli or otherwise, but then we're still back to the fact that environmental changes made the biggest effect, not genetics. Why can't this be the case in your other examples too?
TL;DR: Yes, genetics matter. What's more relevant is, how much?
I've always viewed genetics and talent as essentially your maximum potential. Lots of ways to drag you down from being all that you can be (lead, malnutrition, a good knock on the head), but given a sufficiently good environment, genetics (or perhaps inherent ability might be better) then become the limiting factor on how far you can go.
Your random guy on the street ain't going to be Newton, no matter how much he studies or loves math. Similarly, the man born with muscular dystrophy isn't going to be setting marathon records.
This is a simplification of course, but I hope it conveys the point.
Epigenetics does not change your DNA or what you pass down to your children, and is reversible, so I wouldn't call that "shaping genetics", at least not in the way I was referring to.
But epigenetic changes during foetal development could effect the likelihood of being successful at passing ones genes along at all, although I've no idea how you'd manage to isolate or replicate these effects in any scientifically useful fashion.
Someone in these discussions always brings up epigenetics at some point, its impact there far exceeding its impact on population genetics I would guess :) Nobody ever talks about genetic drift or gene flow however, probably because despite being actual things that affect population genetics talking about "nearly neutral drift in small populations" is really hard to wedge into an ideological shouting match dressed up as a scientific debate.
I understand that some have genetics that make it harder for them to keep off weight, either by metabolism, neural hunger stimuli or otherwise, but then we're still back to the fact that environmental changes made the biggest effect, not genetics. Why can't this be the case in your other examples too?
TL;DR: Yes, genetics matter. What's more relevant is, how much?