If we take the length of the body as the standard of comparison, the limbs of the large rabbits have not increased in length in due proportion by one inch and a half. Again, if we take as the standard of comparison the length of the skull, which, as we have before seen, has not increased in length in due proportion to the length of body, the limbs will be found to be, proportionally with those of the wild rabbit, from half to three-quarters of an inch too short. Hence, whatever standard of comparison be taken, the limb-bones of the large lop-eared rabbits have not increased in length, though they have in weight, in full proportion to the other parts of the frame; and this, I presume, may be accounted for by the inactive life which during many generations they have spent. Nor has the scapula increased in length in due proportion to the increased length of the body.

The capacity of the osseous case of the brain is a more interesting point, to which I was led to attend by finding, as previously stated, that with all domesticated rabbits the length of the skull relatively to its breadth has greatly increased in comparison with that of the wild rabbits. If we had possessed a large number of domesticated rabbits of nearly the same size with the wild rabbits, it would have been a simple task to have measured and compared the capacities of their skulls. But this is not the case: almost all the domestic breeds have larger bodies than wild rabbits, and the lop-eared kinds are more than double their weight. As a small animal has to exert its senses, intellect, and instincts equally with a large animal, we ought not by any means to expect an animal twice or thrice as large as another to have a brain of double or treble the size. (4/27. See Prof. Owen's remarks on this subject in his paper on the 'Zoological Significance of the Brain, etc., of Man, etc.' read before Brit. Association 1862: with respect to Birds see 'Proc. Zoolog. Soc.' January 11, 1848 page 8.) Now, after weighing the bodies of four wild rabbits, and of four large but not fattened lop-eared rabbits, I find that on an average the wild are to the lop-eared in weight as 1 to 2.17; in average length of body as 1 to 1.41; whilst in capacity of skull they are as 1 to 1.15. Hence we see that the capacity of the skull, and consequently the size of the brain, has increased but little, relatively to the increased size of the body; and this fact explains the narrowness of the skull relatively to its length in all domestic rabbits.


I. Length of Skull (inches).

II. Length of Body from Incisors to Anus (inches).

III. Weight of whole Body (pounds and ounces).

IV. Capacity of Skull measured by Small Shot (grains).

V. Capacity calculated according to Length of Skull relatively to that of No. 1 (Wild Rabbit, Kent) (grains).

VI. Difference between actual and calculated capacities of Skulls (grains).

VII. Showing how much per cent the Brain, by calculation according to the length of the Skull is too light (-) or too heavy (+), relatively to the Brain of the Wild Rabbit No. 1.



1. Wild Rabbit, Kent: 3.15 17.4 3,5 972 .. .. +2

2. Wild Rabbit, Shetland Islands: 3.15 .. .. 979 .. .. +2

3. Wild Rabbit, Ireland: 3.15 .. .. 992 .. .. +2

4. Domestic rabbit, run wild, Sandon: 3.15 18.5 .. 977 .. .. +2

5. Wild, common variety, small specimen, Kent: 2.96 17.0 2,14 875 913 38 - 4

6. Wild, fawn-coloured variety, Scotland: 3.1 .. .. 918 950 32 - 3

7. Silver-grey, small specimen, Thetford warren: 2.95 15.5 2,11 938 910 28 +3

8. Feral rabbit, Porto Santo: 2.83 .. .. 893 873 20 +2 9. Feral rabbit, Porto Santo: 2.85 .. ..

Charles Darwin

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