raised in Britain from seed gathered at different altitudes.
Among animals exactly analogous facts occur. When geese
were first introduced into Bogota they laid few eggs at long
intervals, and few of the young survived. By degrees the
fecundity improved, and in about twenty years became equal
to what it is in Europe. The same author tells us that,
according to Garcilaso, when fowls were first introduced
into Peru they were not fertile, whereas now they are
as much so as in Europe. C. Darwin adduced the following
examples. Merino sheep bred at the Cape of Good Hope have
been found far better adapted for India than those imported
from England; and while the Chinese variety of the Ailanthus
silk-moth is quite hardy, the variety found in Bengal will
only flourish in warm latitudes. C. Darwin also called
attention to the circumstance that writers of agricultural
works generally recommend that animals should be removed
from one district to another as little as possible. This
advice occurs even in classical and Chinese agricultural
books as well as in those of our own day, and proves
that the close adaptation of each variety or breed to the
country in which if originated has always been recognized.
Constitutional Adaptation often accompanied by External
Modification.--Although in some cases no perceptible
alteration of form or structure occurs when constitutional
adaptation to Climate has taken place, in others it
is very marked. C. Darwin collected a large number of
cases in his Animals and Plants under Domestication.
In his Contributions to the Theory of Natural Selection
(p. 167), A. R. Wallace has recorded cases of simultaneous
variation among insects, apparently due to climate or
other strictly local causes. He found that the butterflies
of the family Papilionidae, and some others, became
similarly modified in different islands and groups of
islands. Thus, the species inhabiting Sumatra, Java and
Borneo are almost always much smaller than the closely
allied species of Celebes and the Moluccas; the species or
varieties of the small island of Amboyna are larger than
the same species or closely allied forms inhabiting the
surrounding islands; the species found in Celebes possess
a peculiar form of wing, quite distinct from that of the
same or closely allied species of adjacent islands; and,
lastly, numerous species which have tailed wings in India and
the western islands of the Archipelago, gradually lose the
tail as we proceed eastward to New Guinea and the Pacific.
Many of these curious modifications may, it is true, be due
to other causes than climate only, but they serve to show how
powerfully and mysteriously local conditions affect the form
and structure of both plants and animals; and they render it
probable that changes of constitution are also continually
produced, although we have, in the majority of cases, no
means of detecting them. It is also impossible to determine
how far the effects described are produced by spontaneous
favourable variations or by the direct action of local
conditions; but it is probable that in every case both causes
are concerned, although in constantly varying proportions.
Selection and Survival of the Fittest as Agents in
Naturalization. ---We may now take it as an established
fact that varieties of animals and plants occur, both in
domesticity and in a state of nature, which are better or
worse adapted to special climates. There is no positive
evidence that the influence of new climatal conditions
on the parents has any tendency to produce variations in
the offspring better adapted to such conditions. Neither
does it appear that this class of variations are very
frequent. It is, however, certain that whenever any animal
or plant is largely propagated constitutional variations will
arise, and some of these will be better adapted than others
to the climatal and other conditions of the locality. In a
state of nature, every recurring severe winter or otherwise
unfavourable season weeds out those individuals of tender
constitution or imperfect structure which may have got on
very well during favourable years, and it is thus that the
adaptation of the species to the climate in which it has to
exist is kept up. Under domestication the same thing occurs
by what C. Darwin has termed ``unconscious selection.''
Each cultivator seeks out the kinds of plants best suited
to his soil and climate and rejects those which are tender
or otherwise unsuitable. The farmer breeds from such of
his stock as he finds to thrive best with him, and gets
rid of those which suffer from cold, damp or disease. A
more or less close adaptation to local conditions is thus
brought about, and breeds or races are produced which are
sometimes liable to deterioration on removal even to a short
distance in the same country, as in numerous cases quoted
by C. Darwin (Animals and Plants under Domestication).
The Method of Acclimatization.--Taking into consideration
the foregoing facts and illustrations, it may be considered
as proved---1st, That habit has little (though it appears
to have some) definite effect in adapting the constitution of
animals to a new climate; but that it has a decided, though
still slight, influence in plants when, by the process of
propagation by buds, shoots or grafts, the individual can be
kept under its influence for long periods; 2nd, That great
and sudden changes of climate often check reproduction even
when the health of the individuals does not appear to suffer.
In order, therefore, to have the best chance of acclimatizing
any animal or plant in a climate very dissimilar from that of
its native country, and in which it has been proved that the
species in question cannot live and maintain itself without
acclimatization, we must adopt some such plan as the following:--
1. We must transport as large a number as possible of
adult healthy individuals to some intermediate station, and
increase them as much as possible for some years. Favourable
variations of constitution will soon show themselves, and
these should be carefully selected to breed from, the
tender and unhealthy individuals being rigidly eliminated.
2. As soon as the stock has been kept a sufficient time to
pass through all the ordinary extremes of climate, a number
of the hardiest may be removed to the more remote station,
and the same process gone through, giving protection if
necessary while the stock is being increased, but as soon
as a large number of healthy individuals are produced,
subjecting them to ail the vicissitudes of the Climate.
It can hardly be doubted that in most cases this plan would
succeed. It has been recommended by C. Darwin, and at
one of the early meetings of the Societe Zoologique d'
Acclimatation, at Paris, Isodore Geoffroy St Hillaire insisted
that it was the only method by which acclimatization was
possible. But in looking through the long series of volumes
of Reports published by this society, there is no sign that
any systematic attempt at acclimatization has even once been
made. A number of foreign animals have been introduced, and
more or less domesticated, and some useful exotics have been
cultivated for the purpose of testing their applicability to
French agriculture or horticulture; but neither in the case of
animals nor of plants has there been any systematic effort to
modify the constitution of the species, by breeding largely
and selecting the favourable variations that appeared.
Take the case of the Eucalyptus globulus as an example.
This is a Tasmanian gum-tree of very rapid growth and
great beauty, which will thrive in the extreme south of
France. In the Bulletin of the society a large number
of attempts to introduce this tree into general cultivation
in other parts of France are recorded in detail, with the
failure of almost all of them. But no precautions such as
those above indicated appear to have been taken in any of
these experiments; and we have no intimation that either the
society or any of its members are making systematic efforts
to acclimatize the tree. The first step would be, to obtain
seed from healthy trees growing in the coldest climate and at
the greatest altitude in its native country, sowing these very
largely, and in a variety of soils and situations, in a part
of France where the climate is somewhat but not much more
extreme. It is almost a certainty that a number of trees
would be found to be quite hardy. As soon as these produced
seed, it should be sown in the same district and farther north
in a climate a little more severe. After an exceptionally cold
season, seed should be collected from the trees that suffered
least, and should be sown in various districts all over
France. By such a process there can be hardly any doubt
that the tree would be thoroughly acclimatized in any part of
France, and in many other countries of central Europe; and
more good would be effected by one well-directed effort of
this kind than by hundreds of experiments with individual
animals and plants, which only serve to show us which are
the species that do not require to be acclimatized.
Acclimatization of Man.---On this subject we have,
unfortunately, very little direct or accurate information.
The general laws of heredity and variation have been proved
to apply to man as well as to animals and plants; and numerous
facts in the distribution of races show that man must, in
remote ages at least, have been capable of constitutional
adaptation to climate. If the human race constitutes a single
species, then the mere fact that man now inhabits every
region, and is in each case constitutionally adapted to the
climate, proves that acclimatization has occurred. But we have
the same phenomenon in single varieties of man, such as the
American, which inhabits alike the frozen wastes of Hudson's
Bay and Tierra del Fuego, and the hottest regions of the
tropics,---the low equatorial valleys and the lofty plateaux
of the Andes. No doubt a sudden transference to an extreme
climate is often prejudicial to man, as it is to most animals
and plants; but there is every reason to believe that, if
the migration occurs step by step, man can be acclimatized to
almost any part of the earth's surface in comparatively few
generations. Some eminent writers have denied this. Sir Ranald
Martin, from a consideration of the effects of the climate
of India on Europeans and their offspring, believed that there
is no such thing as acclimatization. Dr Hunt, in a report
to the British Association in 1861, argued that ``time is no
agent,'' and--``if there is no sign of acclimatization in one
generation, there is no such process.'' But he entirely ignored
the effect of favourable variations, as well as the direct
influence of climate acting on the organization from infancy.
Professor Theodor Waitz, in his Introduction to Anthropology,
adduced many examples of the comparatively rapid constitutional
adaptation of man to new climatic conditions. Negroes,
for example,who have been for three or four generations
acclimatized in North America, on returning to Africa become
subject to the same local diseases as other unacclimatized
individuals. He well remarked that the debility and
sickening of Europeans in many tropical countries are wrongly
ascribed to the climate, but are rather the consequences of
indolence, sensual gratification and an irregular mode of
life. Thus the English, who cannot give up animal food and
spirituous liquors, are less able to sustain the heat of
the tropics than the more sober Spaniards and Portuguese.
