That is exactly how evolution works. Now if you wanted to argue that evolutionary pressure no longer applied due to modern medicine and safety regulations... you'd still be wrong, but at least you'd look less silly. So there's two kinds of people:

- People who've heard about about the marshmallow impulse control study + the effects that medieval-plagues/cousin-marriage has had on the human gene pool

- People who say silly things like "Modern humanity hasn't existed for an eye blink compared to.."

You're much better off reading a long term study on the life trajectories of people who had their impulse control quantified as children - spoiler: they do not do well in the modern world relative to everyone else enjoying a reduced probability of incarceration.