Part 3 (2/2)

[16] _Life and Letters_, i. p. 16. Darwin's reverence for his father ”was boundless and most touching. He would have wished to judge everything else in the world dispa.s.sionately, but anything his father had said was received with almost implicit faith; ... he hoped none of his sons would ever believe anything because he said it, unless they were themselves convinced of its truth--a feeling in striking contrast with his own manner of faith” (_Life and Letters_, i. pp. 10, 11).

[17] _Ibid._, i. p. 38.

[18] _Life and Letters_, ii. p. 14.

[19] _Origin of Species_, pp. 117, 118.

[20] _Ibid._, p. 180.

[21] _Contemporary Review_, December, 1875, pp. 89, 93.

[22] _Variation of Animals and Plants under Domestication_, i. 292.

[23] _Variation of Animals and Plants under Domestication_, i. 299-301.

[24] To keep pace with this lateral increase in weight, the leg-bones should have lengthened considerably so that their total deficiency in proportional length is 17 per cent.,--a changed proportion which being _linear_ is more excessive than the increase of weight by 28 per cent.

So marked is the effect of the combined thickening and shortening that in the Aylesbury breed--which is the most typically representative one--the leg-bones have become 70 per cent. heavier than they should be if their thickness had continued to be proportional to their length.

[25] This excessive thickening under disuse appears to be due partly to a positive lateral enlargement or increase of proportional weight of about 7-1/2 per cent., and partly to a shortening of about 15 per cent.

Carefully calculated, the reduction of the weight of the wing-bones in this breed is only 83 per cent. relatively to the whole skeleton, or only 5 per cent. relatively to the skeleton _minus_ legs and wings. The latter method is the more correct, since the excessive weight of the leg-bones increases the weight of the skeleton more than the diminished weight of the wing-bones reduces it.

[26] _Variation of Animals and Plants under Domestication_, i. 284.

[27] _Variation of Animals and Plants under Domestication_, i. 184, 185.

[28] _Ibid._, i. 144, 145.

[29] _Ibid._, i. 185.

[30] _Variation of Animals and Plants under Domestication_, i. 175.

[31] _Variation of Animals and Plants under Domestication_, i. 184. I suspect that Darwin was in poor health when he wrote this page. He nods at least four times in it. Twice he speaks of ”twelve” breeds where he obviously should have said eleven.

[32] If a prominent breast is admired and selected by fanciers, the sternum might shorten in a.s.suming a more forward and vertical position.

If the shortening of the sternum is entirely due to disuse, it seems strange that Darwin has not noticed any similar shortening in the sternum of the duck. But selection has not tended to make the duck elegant, or ”pigeon-breasted”; it has enlarged the abdominal sack instead, besides allowing the addition of an extra rib in various cases.

[33] _Variation of Animals and Plants under Domestication_, 144, 175.

[34] _Variation of Animals and Plants under Domestication_, i. 179.

[35] In the six largest breeds the shortening of the sternum is nearly twice as great as in the three smaller breeds which remain nearest the rock-pigeon in size. We can hardly suppose that use-inheritance especially affects the eight breeds that have varied most in size. If we exclude these, there is only a total shortening of 7 per cent. to be accounted for.

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