"Heredity is a convenient term for the genetic relation between successive generations."—"Heredity determines the individual life."—J. Arthur Thomson.
"Life is short and the art long; the occasion fleeting; experience fallacious and judgment difficult."—"It is the business of the physician to know, in the first place, things similar and things dissimilar." Thus spoke the Father of Medicine.
Human experience teaches that like tends to beget like in the propagation of plants and animals. Yet no two are exactly alike. Resemblances, similarities and differences are found among individuals of any species, but Nature has produced no duplicates. Each individual is truly the first and last of its particular kind. However close may be the kinship of individual A and individual B, they are never equal in their natural endowments. A is always more or less competent than B in structure and function; always more or less competent than B in capacities for