3. Glabella, chin, clavicle.
4. Palm, buttock, popliteal space.
5. Neck.
6. Back.
7. Lower eyelid, cheek.
8. Nipple, loin.
These two tables show the great differences in the range of sensitiveness to cold and to warmth in different parts of the body. I doubt if any one will attempt to show that these differences of range of sensation can be accounted for either by natural selection or by the Lamarckian hypothesis.
Of course, it does not necessarily follow that, because this is true for the warm and cold spots, that it must also be true for the tactile organs; but I think that the fact of such a great difference in the responsiveness to cold and to warmth in different parts of the body should put us on our guard against a too ready acceptation of Spencer’s argument. More especially is this seen to be necessary, when, as has been shown above, the distribution of the touch-organs themselves by no means closely corresponds to what we should expect, if they have developed in response to contact, as Spencer maintains.
The other main argument advanced by Spencer to fortify the theory of the inheritance of acquired characters, and at the same time to show the inadequacy of the theory of natural selection, is based on the idea of what he calls the “coöperation of the parts” that is required in order to carry out any special act. Spencer contends that “the relative powers of coöperative parts cannot be adjusted solely by the survival of the fittest, and especially where the parts are numerous and the coöperation complex.”
Spencer illustrates his point by the case of the extinct Irish elk, whose immensely developed horns weighed over a hundredweight. The horns, together with the massive skull, could not have been supported by the outstretched neck without many and great changes of the muscles and bones of the neck and of the fore-part of the body. Unless, for instance, the fore-legs had been also strengthened, there would be failure in fighting and in locomotion. Since “we cannot assume spontaneous increase of all these parts proportionate to the additional strains, we cannot suppose them to increase by variations one at once, without supposing the creature to be disadvantaged by the weight and nutrition of the parts that were for a time useless,—parts, moreover, which would revert to their original sizes before the other needful variations occurred.”