But the discovery that the bug has the ability to survive milk processing is likely to provoke calls to research the issue.

BBC: Minister declares milk 'safe'

One gene that spread in many parts of Europe along with the migrants gave adults lactose tolerance, or the ability to digest milk.

WSJ: Migrations Spurred Agriculture Spread, Studies Indicate

These hormones include cortisol (which is related to stress), estradiol (the main female sex hormone) and prolactin (which, as its name suggests, triggers her breast tissue to develop the ability to secrete milk).

ECONOMIST: Hormones and fatherhood