it's easy enough to piece together a theory that ice age humans may have been unable to access sufficient minerals from the soil (because it was frozen, or hidden underneath the snow and ice) and consequently adjusted by relying on meat for mineral absorption, instead. in the process, those who could best utilize the minerals in meat were most successful. so, those genes were passed on.

but, that would have only been true in areas affected by the ice age.

in warmer climates, those evolutionary pressures would have been limited, and the reliance on the soil for minerals would have continued.