The Foundations of the Origin of Species: Two Essays written in 1842 and 1844

ON THE VARIATION OF ORGANIC BEINGS UNDER

DOMESTICATION; AND ON THE PRINCIPLES OF

SELECTION

T

he most favourable conditions for variation seem to be when organic be-

ings are bred for many generations under domestication{186}: one may

infer this from the simple fact of the vast number of races and breeds of

almost every plant and animal, which has long been domesticated. Under

certain conditions organic beings even during their individual lives become

slightly altered from their usual form, size, or other characters: and many

of the peculiarities thus acquired are transmitted to their offspring. Thus in

animals, the size and vigour of body, fatness, period of maturity, habits of

body or consensual movements, habits of mind and temper, are modified or

acquired during the life of the individual{187}, and become inherited. There

is reason to believe that when long exercise has given to certain muscles great

development, or disuse has lessened them, that such development is also in-

herited. Food and climate will occasionally produce changes in the colour

and texture of the external coverings of animals; and certain unknown con-

3 CHARLES DARWIN

ditions affect the horns of cattle in parts of Abyssinia; but whether these pe-

culiarities, thus acquired during individual lives, have been inherited, I do

not know. It appears certain that malconformation and lameness in horses,

produced by too much work on hard roads, -that affections of the eyes in

this animal probably caused by bad ventilation, -that tendencies towards

many diseases in man, such as gout, caused by the course of life and ulti-

mately producing changes of structure, and that many other diseases pro-

duced by unknown agencies, such as goitre, and the idiotcy resulting from

it, all become hereditary.

{186} The cumulative effect of domestication is insisted on in the Origin, see

e.g. Origin, Ed. i. p. 7, vi. p. 8.

{187} This type of variation passes into what he describes as the direct effect

of conditions. Since they are due to causes acting during the adult life of the

organism they might be called individual variations, but he uses this term for

congenital variations, e.g. the differences discoverable in plants raised from

seeds of the same pod (Origin, Ed. i. p. 45, vi. p. 53).

It is very doubtful whether the flowers and leaf-buds, annually produced

from the same bulb, root, or tree, can properly be considered as parts of the

same individual, though in some respects they certainly seem to be so. If they

are parts of an individual, plants also are subject to considerable changes dur-

ing their individual lives. Most florist-flowers if neglected degenerate, that

is, they lose some of their characters; so common is this, that trueness is of-

ten stated, as greatly enhancing the value of a variety{188}: tulips break their

colours only after some years' culture; some plants become double and oth-

ers single, by neglect or care: these characters can be transmitted by cuttings

or grafts, and in some cases by true or seminal propagation. Occasionally

a single bud on a plant assumes at once a new and widely different charac-

ter: thus it is certain that nectarines have been produced on peach trees and

moss roses on provence roses; white currants on red currant bushes; flowers

of a different colour from that of the stock, in Chrysanthemums, Dahlias,