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Show 142 LAWS OF VARIATION. [CHAP, V. ives fewer offspring to the less fav?~red males. What~ ~ver the cause may be of the vanabi~Ity of secondary s~x~ ual characters, as they are highly varia]:>le, sexual selection will have had a wide scope for action, and ~ay thus readily have succeeded in giving to the _speme.s of the same group a greater ainount of diffe.rence In thell' sexual characters, than in other parts of theu structure. . It is a remarkable fact, that the secondary sexu.al chfferences between the two sexes of the same species ar.e generally displayed in ~he very sa~e parts of the }organisation in which the different speCies of ~he ~am~ g:enus differ from each other. Of this fact I will g1ve In Illustration two instances, the first which· happen to stand on my list ; and as the differences in these cases are o~ a very unusual nature the relation can hardly be accidental. The same number of joints in the tarsi is a characte~ generally common to very large groups of beetles, but In t!1e Engidre, as Westwood has. re~arke.d, th~ number vanes greatly ; and the numbc~ h_kew1se drf~fers In the two sexes of the same species : again In a fossonal hymenoptera, the manner of neuration of the wings is a character of tho highest importance, because co;n~o:r: t? large grou~s ; but in certain genera the neuratlon differs In the differ~nt ·species, and likewise in the tw_o sexes of t~e same species. This relation has a clear meanmg on my view of the subject: I look at all the species of the same gen~s as having as certainly descended from the same progemtor, as have the two sexes of any one of the species. Consequently, whatever part of the structure of the con;mon prog~n~tor, or of its early descendants, became vanable ; variations of this part would, it is highly probable, be taken advantage of by natural and sexual selection, in order to fit the several species to their several places in the economy of nature, and likewise to fit the two sexes of the same sp.ecies to each other, or to fit the Inales and females to different habits of life, or the males to struggle with other males for the possession of the females. . . . Finally, then, I conclude that the greater variabibty of specific characters, or those which distinguish species from species, than of generic characters, or those which the OII.AP. V.] LAWS OF VARIATION. 143 spe?ie~ :possess in common ;-that the frequent extrem varia"b't ihty do'f any part whic. h is developed 1· n a spem·e s I. ne an e~ r~or 1nary manner In comparison with the same p~::t 1:r: Its congeners ; and the not great degree of variablhty ~n .a part, however extraordinarily it may be developed, 1f 1t be .co~~on to a whole group of species ;-that the great var1ab1hty of secondary sexual characters and the great amount of difference in these same char~cters bet:vee:r; closel:y: allie~ species ;-that secondary sexual and ordinarily specific differences are generally displayed in the same parts of the organisation,-are all principles clo~~ly connected together. All being mainly due to the spemes of t~e same group having descended from a comInon progenitor, from whom they have inherited much in co~mon, -. to part~ whic~ have recently and largely var;ed bmng more hkely still to go on varyino- than parts whwh have long been inherited and have not varied -to ~atural selection having more or less completely, ac~ordlng ~o the lapse of time, overmastered the tendency to reve:; slon an~ ~o further variability,-to sexual selection ?mng less ngid than ordinary selection,-and to variations 1n the san1e parts having been accumulated by natural and sexual selecti?n, and tP,us adapted for secondary sexual, and for ordinary specific purposes. .[Jistinct specie~ present analogous variations j and ~ var~ety of. one sp~c~es often assu?nes some of the characters vf an allMd spem~~s, or reverts to some of the characters of an ~arly progen~tor.-These propositions will be most read1ly und~r~tood by looking to our domestic races. T~e most distinct breeds of pigeons, in countries most Widely apart, present sub-varieties with reversed feathers on the head and fe.at?ers on the feet,-characters not possessed by t~e ~bori_ginal rock-pigeon; these then are analogous variations ~n two or more distinct races. The frequent presence of fourteen or even sixteen tailfeathers in t~e pouter, may be considered as a variation representing t e normal structure of another race, the fantail. I pre~ s~me that no one will doubt that all such analogous varia4 tlons are due to the several races of the pigeon having |