Chapter V: Heredity and the Origin of Variations (3)

But there is no reason why such influence should not be assumed as a provisional hypothesis.

NOTES

[BD] "Animals and Plants under Domestication," vol ii. p. 239.

[BE] Or in certain "physiological units" (Herbert Spencer), or
"plastidules" (Haeckel), which may be regarded as organic
molecules exhibiting their special properties under vital
conditions.

[BF] _Nature_, vol. xxxix. p. 486.

[BG] Darwin, "Animals and Plants under Domestication," 2nd edit., vol.
ii. chap. xxvii., from which the following description and
quotations are taken.

[BH] For an excellent account of the genesis and growth of the modern
views of heredity, see Mr. J. Arthur Thomson's paper on "The
History and Theory of Heredity:" Proceedings of the Royal Society
of Edinburgh, 1889.

[BI] Geddes and Thomson, "The Evolution of Sex," p. 92.

[BJ] Weismann, "Essays on Heredity," English translation, p. 173.

[BK] Weismann, "Essays on Heredity," p. 205.

[BL] A few pages earlier (p. 200) in the same essay, Professor Weismann
says, "A sudden transformation of the nucleo-plasm of a somatic
cell into that of a germ-cell would be almost as incredible as the
transformation of a mammal into an am[oe]ba." This at first sight
does not seem quite consistent with the subsequent sentence which
I have quoted in the text; for here, at any rate, the daughters of
"mammals" are said to be converted into "am[oe]bæ." But this is no
doubt because the am[oe]bæ (germ-plasms) are _contained in_ the
mammals (body-cells). (See the quotations that follow in the
text.)

[BM] Weismann, "Essays on Heredity," p. 207.

[BN] Weismann, "Essays on Heredity," p. 179.

[BO] It will, of course, be understood that a minute fragment of
germ-plasm is capable of almost unlimited growth by assimilation
of nutritive material, its properties remaining unchanged during
such growth.

[BP] Latency is here neglected. Mr. Francis Galton has shown,
statistically, that the offspring, among human folk, inherit 1/4
from each parent, 1/16 from each grandparent, and the remaining
1/4 from more remote ancestors. In domesticated animals, reversion
to characters of distant ancestors sometimes occurs. This,
however, does not invalidate the argument in the text, which is
that sexual admixture tends towards the mean of the race
(ancestors included), and cannot be credited with new and
unusually favourable variations. The prepotency of one parent is
also here neglected.

[BQ] See his valuable paper on "Divergent Evolution," Lin. Soc. Zool.,
No. cxx.

[BR] One parthenogenetic form--the drone--has been shown by Blochmann
to extrude a second polar cell. This observation is in serious
opposition to Dr. Weismann's theory.

[BS] Weismann, "Essays on Heredity," pp. 355, 378.

[BT] The law of compensation of growth or balancement was suggested at
nearly the same time by Goethe and Geoffrey Saint-Hilaire. The
application in the text has not, so far as I know, been before
suggested.

[BU] Darwin spoke of changed conditions acting "directly on the
organization or indirectly through the reproductive system." Now,
since Professor Weismann has taught us to reconsider these
questions, we speak of such conditions as acting directly on the
germ or indirectly through the body. The germ is no longer
subordinate to the body, but the body to the germ.

[BV] July 15, 1876. Since reprinted in "The Advancement of Science," p.
273.

[BW] Herbert Spencer, "Principles of Biology," vol. i. p. 256.

[BX] Mr. J. A. Thomson has published a most valuable "Synthetic Summary
of the Influence of the Environment upon the Organism"
(Proceedings Royal Physiological Society, Edinburgh: vol. ix. pt.
3, 1888). The case of the Amazonian parrots was communicated to
Darwin by Mr. Wallace ("Animals and Plants under Domestication,"
vol. ii. p. 269).

[BY] St. George Mivart, "On Truth," p. 378.

[BZ] _Op. cit._, p. 47. I venture to say, "with some assurance,"
because Charles Darwin, who had also considered this matter,
writes, "Who will pretend to decide how far the thick fur of
Arctic animals, or their white colour, is due to the direct action
of a severe climate, and how far to the preservation of the
best-protected individuals during a long succession of
generations?" ("Animals and Plants under Domestication," p. 415).

[CA] "Organic Evolution," English translation, p. 88.

[CB] "Contributions to Natural Selection," p. 197.

[CC] Since this was written, Mr. Poulton has described his results in
an interesting volume on "The Colours of Animals" (_q.v._).

[CD] See _Journal of Anatomy and Physiology_, vol. xxii. p. 215.

[CE] See Professor Herdman's Inaugural Address, Liverpool Biological
Society, 1888.

[CF] Francis Galton, "Inquiries into Human Faculty," p. 216.

[CG] That the epidermis is thicker on the palms of the hands and the
soles of the feet in the infant long before birth, may be
attributable to the inherited effects of use or pressure. It can
hardly be held that the thickening of the skin in these parts is
of elimination value.

[CH] The instances cited are from "Animals and Plants under
Domestication."