with white hairs mixing in

(A)

Hair grows slowly from deep in your skin with the growing hair under the skin pushing the visible ends forward. So the only living part of your hair is underneath the skin, while all the hair that you see above the surface is dead and cannot change color. Hair gets its color from cells containing a pigment called melanin, which is found only in living hairs underneath your skin. You develop gray hair when the living cells underneath your skin stop making melanin, and this happens slowly with aging. Some hairs have their normal color, but the ones without melanin will be completely white. So there is no such thing as gray-colored hair. Gray hair is dark hairs with white hairs mixing in.

 

(B)

Lorenz devoted much of his time to observe birds, including geese. From these observations came one of his most important discoveries. In 1935, Lorenz concluded that if a mother goose is not present when her baby geese hatch, they will consider the first moving object they see being their mother. Lorenz found that if the moving object happened to be himself, the baby geese would follow him as if he were their mother. He found this to be true with ducks, too. Lorenz called this behavior imprinting. Imprinting is important because in order for baby animals to survive, they must recognize a mother who will feed and protect them.