important are hardly perceptible to any one but a
naturalist--are usually not found in the same but in widely separated
countries. Thus, the nearest allies to our European golden plover are
found in North America and East Asia; the nearest ally of our European
jay is found in Japan, although there are several other species of jays
in Western Asia and North Africa; and though we have several species of
titmice in England they are not very closely allied to each other. The
form most akin to our blue tit is the azure tit of Central Asia (Parus
azureus); the Parus ledouci of Algeria is very near our coal tit, and
the Parus lugubris of South-Eastern Europe and Asia Minor is nearest to
our marsh tit. So, our four species of wild pigeons--the ring-dove,
stock-dove, rock-pigeon, and turtle-dove--are not closely allied to each
other, but each of them belongs, according to some ornithologists, to a
separate genus or subgenus, and has its nearest relatives in distant
parts of Asia and Africa. In mammalia the same thing occurs. Each
mountain region of Europe and Asia has usually its own species of wild
sheep and goat, and sometimes of antelope and deer; so that in each
region there is found the greatest diversity in this class of animals,
while the closest allies inhabit quite distinct and often distant areas.
In plants we find the same phenomenon prevalent. Distinct species of
columbine are found in Central Europe (Aguilegia vulgaris), in Eastern
Europe, and Siberia (A. glandulosa), in the Alps (A. Alpina), in the
Pyrenees (A. pyrenaiea), in the Greek mountains (A. ottonis), and in
Corsica (A. Bernardi), but rarely are two species found in the same
area. So, each part of the world has its own peculiar forms of pines,
firs, and cedars, but the closely allied species or varieties are in
almost every case inhabitants of distinct areas. Examples are the deodar
of the Himalayas, the cedar of Lebanon, and that of North Africa, all
very closely allied but confined to distinct areas; and the numerous
closely allied species of true pine (genus Pinus), which almost always
inhabit different countries or occupy different stations. We will now
consider some other modes in which natural selection will act, to adapt
organisms to changed conditions.

_Adaptation to Conditions at Various Periods of Life._

It is found, that, in domestic animals and cultivated plants, variations
occurring at any one period of life reappear in the offspring at the