It's clear that agricultural societies were more fit than hunter-gatherer societies.
Agricultural societies could breed more people and use them to kill the hunter-gatherers and take their land.
Even if the meat/vegetable eaters were bigger and stronger than the grain eaters, there were simply a lot more grain eaters.
Classic Greek myths are full of references to "golden age" men who were displaced by more degenerate modern, civilized men. I can't help read those myths as a story of the rise of agriculture.
> [Men] lived like gods without sorrow of heart, remote and free from toil and grief: miserable age rested not on them; but with legs and arms never failing they made merry with feasting beyond the reach of all devils. When they died, it was as though they were overcome with sleep, and they had all good things; for the fruitful earth unforced bare them fruit abundantly and without stint. They dwelt in ease and peace.
> In the 5th century BCE, the philosopher Empedocles, like Hesiod before him, emphasized the idea of primordial innocence and harmony in all of nature, including human society, from which he maintained there had been a steady deterioration until the present.
My original question was a bit cheeky as I already knew the answer.
The Icelandic ancestors didn't have that luxury in their country's bitter cold