On The Origin of Species by Charles Darwin Chapter 1 Page 17

in two large volumes, is the fullest and the best on this subject. No breeder doubts how strong is the tendency to inheritance; that like produces like is his fundamental belief: doubts have been thrown on this principle only by theoretical writers. When any deviation of structure often appears, and we see it in the father and child, we cannot tell whether it may not be due to the same cause having acted on both; but when among individuals, apparently exposed to the same conditions, any very rare deviation, due to some extraordinary combination of circumstances, appears in the parent — say, once among several million individuals — and it reappears in the child, the mere doctrine of chances almost compels us to attribute its reappearance to inheritance.

Every one must have heard of cases of albinism, prickly