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Descent of Man [ 1871]

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Author Topic: Descent of Man [ 1871]  (Read 2888 times)
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« on: February 09, 2009, 01:09:01 pm »

The Direct and Definite Action of Changed Conditions.- This is a
most perplexing subject. It cannot be denied that changed conditions
produce some, and occasionally a considerable effect, on organisms
of all kinds; and it seems at first probable that if sufficient time
were allowed this would be the invariable result. But I have failed to
obtain clear evidence in favour of this conclusion; and valid
reasons may be urged on the other side, at least as far as the
innumerable structures are concerned, which are adapted for special
ends. There can, however, be no doubt that changed conditions induce
an almost indefinite amount of fluctuating variability, by which the
whole organisation is rendered in some degree plastic.
  In the United States, above 1,000,000 soldiers, who served in the
late war, were measured, and the States in which they were born and
reared were recorded.* From this astonishing number of observations it
is proved that local influences of some kind act directly on
stature; and we further learn that "the State where the physical
growth has in great measure taken place, and the State of birth, which
indicates the ancestry, seem to exert a marked influence on the
stature." For instance, it is established, "that residence in the
Western States, during the years of growth, tends to produce
increase of stature." On the other hand, it is certain that with
sailors, their life delays growth, as shewn "by the great difference
between the statures of soldiers and sailors at the ages of
seventeen and eighteen years." Mr. B. A. Gould endeavoured to
ascertain the nature of the influences which thus act on stature;
but he arrived only at negative results, namely that they did not
relate to climate, the elevation of the land, soil, nor even "in any
controlling degree" to the abundance or the need of the comforts of
life. This latter conclusion is directly opposed to that arrived at
by, Villerme, from the statisties of the height of the conscripts in
different parts of France. When we compare the differences in
stature between the Polynesian chiefs and the lower orders within
the same islands, or between the inhabitants of the fertile volcanic
and low barren coral islands of the same ocean,*(2) or again between
the Fuegians on the eastern and western shores of their country, where
the means of subsistence are very different, it is scarcely possible
to avoid the conclusion that better food and greater comfort do
influence stature. But the preceding statements shew how difficult
it is to arrive at any precise result. Dr. Beddoe has lately proved
that, with the inhabitants of Britain, residence in towns and
certain occupations have a deteriorating influence on height; and he
infers that the result is to a certain extent inherited, as is
likewise the case in the United States. Dr. Beddoe further believes
that wherever a "race attains its maximum of physical development,
it rises highest in energy and moral vigour."*(3)

  * Investigations in Military and Anthrop. Statistics, &c., 1869,
by B. A. Gould, pp. 93, 107, 126, 131, 134.
  *(2) For the Polynesians, see Prichard's Physical History of
Mankind, vol. v., 1847, pp. 145, 283. Also Godron, De l'Espece, tom.
ii., p. 289. There is also a remarkable difference in appearance
between the closely-allied Hindoos inhabiting the Upper Ganges and
Bengal; see Elphinstone's History of India, vol. i., p. 324.
  *(3) Memoirs, Anthropological Society, vol. iii., 1867-69, pp.
561, 565, 567.

 Whether external conditions produce any other direct effect on man is
not known. It might have been expected that differences of climate
would have had a marked influence, inasmuch as the lungs and kidneys
are brought into activity under a low temperature, and the liver and
skin under a high one.* It was formerly thought that the colour of the
skin and the character of the hair were determined by light or heat;
and although it can hardly be denied that some effect is thus
produced, almost all observers now agree that the effect has been very
small, even after exposure during many ages. But this subject will
be more properly discussed when we treat of the different races of
mankind. With our domestic animals there are grounds for believing
that cold and damp directly affect the growth of the hair; but I
have not met with any evidence on this head in the case of man.

  * Dr. Brakenridge, "Theory of Diathesis," Medical Times, June 19 and
July 17, 1869.

  Effects of the increased Use and Disuse of Parts.- It is well
known that use strengthens the muscles in the individual, and complete
disuse, or the destruction of the proper nerve, weakens them. When the
eye is destroyed, the optic nerve often becomes atrophied. When an
artery is tied, the lateral channels increase not only in diameter,
but in the thickness and strength of their coats. When one kidney
ceases to act from disease, the other increases in size, and does
double work. Bones increase not only in thickness, but in length, from
carrying a greater weight.* Different occupations, habitually
followed, lead to changed proportions in various parts of the body.
Thus it was ascertained by the United States Commission*(2) that the
legs of the sailors employed in the late war were longer by 0.217 of
an inch than those of the soldiers, though the sailors were on an
average shorter men; whilst their arms were shorter by 1.09 of an
inch, and therefore, out of proportion, shorter in relation to their
lesser height. This shortness of the arms is apparently due to their
greater use, and is an unexpected result: but sailors chiefly use
their arms in pulling, and not in supporting weights. With sailors,
the girth of the neck and the depth of the instep are greater,
whilst the circumference of the chest, waist, and hips is less, than
in soldiers.

  * I have given authorities for these several statements in my
Variation of Animals and Plants under Domestication, vol. ii., pp.
297-300. Dr. Jaeger, "Uber das Langenwachsthum der Knochen," Jenaische
Zeitschrift, B. v., Heft. i.
  *(2) Investigations, &c., by B. A. Gould, 1869, p. 288.
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