46 THE DESCENT OP MAN. 



creased; or that, as each district became fully stocked, this same 

 power was diminished. No doubt in this case, and in all other-, 

 many checks concur, and different checks under different circum- 

 stances; periodical dearths, depending on unfavorable seasons, 

 being probably the most important of all. So it will have been 

 with the early progenitors of man. 



Nutm-dl Selection. — We have now seen that man Is variable in 

 body and mind; and that the variations are induced, either di- 

 rectly or indirectly, by the same general causes, and obey the 

 same general laws, as with the lower animals. Man has spread 

 widely over the face of the earth, and must have been exposed, 

 during his incessant migrations,"" to the most diversified condi- 

 tions. The Inhabitants of Tierra del Fuego, the Cape of Good 

 Hope, and Tasmania in the one hemisphere, and of the Arctic 

 regions in the other, must have passed through many climates, 

 and changed their habits many times, before they reached their 

 present homes." The early progenitors of man must also have 

 tended, like all other animals, to have increased beyond their 

 means of subsistence; they must, therefore occasionally have been 

 exposed to a struggle for existence, and consequently to the rigid 

 law of natural selection. Beneficial variations of all kinds will 

 thus, either occasionally or habitually, have been preserved, and 

 injurious ones eliminated. I do not refer to strongly-marked de- 

 viations of structure, which occur only at long intervals of time, 

 but to mere individual differences. We know, for instance, that 

 the muscles of our hands and feet, which determine our powers of 

 movement, are liable, like those of the lower animals,"" to incessant 

 variability. If then the progenitors of man Inhabiting any dis- 

 trict, especially one undergoing some change in its conditions, 

 were divided into two equal bodies, the one halt which included all 

 the Individuals best adapted by their powers of movement for gain- 

 ing subsistence, or for defending themselves, would on an average 

 survive in greater numbers, and procreate more offspring than the 

 other and less well endowed half. 



Man in the rudest state in which he now exists is the most domi- 

 nant animal that has ever appeared on this earth. He has spread 

 more widely than any other highly organized form; and all others 

 have yielded before him. He manifestly owes this Immense superi- 



or See some g-ood remarks to this effect by W. Stanley Jevons, "A 

 "Deduction from Darwin's Theory," 'Nature,' 1869, p. 231. 



'* Latham, 'Man and his Migrations,' 1S51, p. 135. 



«= Messrs. Murie and Mivart in their 'Anatomy of the L^muroidea' 

 ('Transact. Zoolog. Soc. vol. vii. 1869, pp. 96-98) say, "some muscles are 

 "so irregular in their distribution that they cannot be well classed in 

 "any of the above groups." These muscles differ even on the oppo- 

 site sides of the same individual. 



