sure causes individuals to vary; but if
these individuals continue to live and to be reproduced under the same
difference of circumstances, distinctions are brought about in them
which become in some degree essential to their existence. In a word, at
the end of many successive generations, these individuals, which
originally belonged to another species, are transformed into a new and
distinct species.[791]

Thus, for example, if the seeds of a grass, or any other plant which
grows naturally in a moist meadow, be accidentally transported, first to
the slope of some neighboring hill, where the soil, although at a
greater elevation, is damp enough to allow the plant to live; and if,
after having lived there, and having been several times regenerated, it
reaches by degrees the drier and almost arid soil of a mountain
declivity, it will then, if it succeeds in growing, and perpetuates
itself for a series of generations, be so changed that botanists who
meet with it will regard it as a particular species.[792] The
unfavorable climate in this case, deficiency of nourishment, exposure to
the winds, and other causes, give rise to a stunted and dwarfish race,
with some organ more developed than others, and having proportions often
quite peculiar.

What nature brings about in a great lapse of time, we occasion suddenly
by changing the circumstances in which a species has been accustomed to
live. All are aware that vegetables taken from their birthplace, and
cultivated in gardens, undergo changes which render them no longer
recognizable as the same plants. Many which were naturally hairy become
smooth, or nearly so; a great number of such as were creepers and
trailed along the ground, rear their stalks and grow erect. Others lose
their thorns or asperities; others, again, from the ligneous state which
their stem possessed in hot climates, where they were indigenous, pass
to the herbaceous; and, among them, some which were perennials become
mere annuals. So well do botanists know the effects of such changes of
circumstances, that they are averse to describe species from garden
specimens, unless they are sure that they have been cultivated for a
very short period.

"Is not the cultivated wheat" (_Triticum sativum_), asks Lamarck, "a
vegetable brought by man into the state in which we now see it? Let any
one tell me in what country a similar plant grows wild, unless where it
has escaped from cultivated fields? Where do we find in n