THE VEGETABLE AND ANIMAL KINGDOMS. 145 



tration of the principle of development, although in an 

 operation limited to the production of sex only. Let it not be 

 said that the phenomena concerned in the generation of bees 

 may be very different from those concerned in the reproduction 

 of the higher animals. There is a unity throughout nature, 

 which makes the one case an instructive reflection of the 

 other. 1 



We shall now see an instance of development operating 

 within the production of what approaches to the character of 

 variety of species. It is fully established that a human family, 

 tribe, or nation, is liable, in the course of generations, to be either 

 advanced from a mean form to a higher one, or degraded from a 

 higher to a lower, by the influence of the physical conditions in 

 which it lives. The coarse features and other structural pecu- 

 liarities of the negro race only continue while these people live 

 amidst the circumstances usually associated with barbarism. In 

 a more temperate clime, and higher social state, the face and 

 figure become greatly refined. The few African nations which 

 possess any civilization exhibit forms approaching the Euro- 

 pean j and when the same people in the United States of 

 America have enjoyed a within-door life for several generations, 

 they assimilate to the whites amongst whom they live. On 

 the other hand, there are authentic instances of a people 

 originally well-formed and good-looking being brought, by 

 imperfect diet and a variety of physical hardships, to a meaner 

 form. It is remarkable that prominence of the jaws, a reces- 

 sion and diminution of the cranium, and an elongation and 

 attenuation of the limbs, are peculiarities always produced by 

 these miserable conditions, for they indicate an unequivocal 

 retrogression towards the type of the lower animals. Thus we 

 see nature alike willing to go back and to go forward. Both 

 effects are simply the result of the operation of the law of 

 development in the generative system. 



Let us trace this law also in the production of certain classes 

 of monstrosities. A human foetus is often left with one of the 

 most important parts of its frame imperfectly developed ; the 

 heart, for instance, goes no further than the three-chambered 



1 M. Hampe has observed in the creeping willow (salix repens) that 

 twigs above the water blossom as females, whilst those twigs which have 

 been in the water, and subsequently blossomed when the water dried up, 

 had only male blossoms. This seems a case analogous to that of the 

 determination of sex by the bees, and may be held as an additional 

 proof of the power of circumstances to affect development to very im- 

 portant results. 



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