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Show 248 THE DESCENT OF MAN. PAUl' I. jecting supra-orbital ridges. It is not improbable that the texture of the hair, which differs much in the different races, may stand in some kind of correlation with the structure of the skin ; for the colour of the hail~ and skin are certainly correlated, as is its colour and texture with the 1\fandans. 53 The colour of the skin and the odour emitted by it are likewise in some manner connected. With the breeds of sheep the number of hairs within a given space and the number of the excretory pores stand in some relation to each other.5 .. If we may judge from the analogy of our domesticated animals, many modifications of structure in man probably come under this principle of correlated growth. vVe have now seen that the characteristic differences between the races of man cannot be accounted for in a satisfactory manner by the direct action of the conditions of life, nor by the effects of the continued use of parts, nor through the principle of correlation. We a~e therefore led to inquire whether slight individual differences, to which man is eminently liable, may not have been preserved and augmented during a long series of generations through natural selection. But here we are at once met by the objection that beneficial variations alone can be thus preserved; and as far as we are enabled to judge (although always liable to error on this head) not one of the external differences between the races of man are of any Jirect or 53 Mr ... Catlin states (' .N. Amu·icnn Indians,' 3rtl edit. 1842, vol. i. p. 49) tuat m the whole tnbe of the Mandans, about one in ten or twelve of t.he ~ember~ of all ages and both sexes have bright silvery grey hair, which 1s hereditary. Now this hair is as coarse and harsh as that of a hor~e's mane, whilst the hair of other colours is fine and soft. 54 On the ?dour of :he skin, Godron, 'Sur l.'Espece,' tom. ii. p. 217. On the pores m the skm, Dr. Wilckens, 'Die Auf,.aben der landwirth. Zoot ~choik,' 18G9, s. 7. o CHAP. VII. THE RACES OF l\1AN. 249 special service to him. The intellectual and moral or social faculties must of course be excepted from this remark · but differences in these faculties can have had little ~r no influence on external characters. The variabilitv of all the characteristic differences between the races,· before referred to, likewise indicates that these differences cannot be of much importance ; for, had they been important, they would long ago have bee? either fixed and preserved, or eliminated. In th1s respect man resembles those forms, called by naturalists protean or polymorphic, which have remained extremely variable, owing, as it seems, to their variations being of an indifferent nature, and consequently to theiL· having escaped the action of natural selection. We have thus far been baffled in all our attempts to account for the differences between the races of man ; but there remains one important agency, namely Sexual Selection, which appears to have acted as powerfully on man, as on many other animals. I do not intend to assert that sexual selection will account for all the differences between the races. An unexplained residuum is left, about which we can in our ignorance only say, that as individuals are continually born with, for instance, heads a little rounder or narrower, and with noses a little longer or shorter, such slight differences might become fixed and uniform, if the unknown agencies which induced them were to act in a more constant manner, aided by long-continued intercrossing. Such modifications come under the provisional class, alluded to in our fourth chapter, which for the want of a better term have been called spontaneous variations. Nor do I pretend that the effects of sexual selection can be indicated with scientific precision; but it can be shewn that it would be an inexplicable fact if man had not been modified by this agency, which Las |
