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,
