[electromagnetic]

IIRC lactose tolerance is only believed to have become endemic since about 8000 years ago, incidentally right around when agriculture hit the big time.

I wonder if the control of pasture lands necessitated the higher calorific quantity an animal provides when it is milked. Less herd land means a farmer would need to extract more calories per animal to survive. Similarly less migration also means less danger and higher populations, which again require more calories per animal to sustain.