There does not appear at first sight to be much connection between such distinct and apparently disconnected phenomena as 1, the orderly normal progress of development; 2, atavism and the resumption of feral characteristics; 3, the more ordinary resemblance inter se of nearer relatives; 4, the benefit of an occasional cross, and the usual sterility of hybrids; 5, the unconsciousness with which alike bodily development and ordinary physiological functions proceed, so long as they are normal; 6, the ordinary non-inheritance, but occasional inheritance of mutilations; 7, the fact that puberty indicates the approach of maturity; 8, the phenomena of middle life and old age; 9, the principle underlying longevity.
— from Essays on Life, Art and Science by Samuel Butler