221 
propagation), each parent gives one half of the resulting 
being.* 
Another source of variety is the dissimilarity of race 
amongst mankind. This is as great as can be deemed con- 
sistent with a common origin, and once markedly impressed 
seems to be almost imperishable. The resemblance of ancient 
types to their modern representatives has been abundantly 
illustrated by Cuvier and those who have succeeded him. I do 
not see how this differentiation can have been caused by 
external circumstances, as it penetrates so deeply into the 
physical structure. A white man will become dai’k- coloured by 
exposure to an African sun, but he would never acquire the 
peculiarities of a negro, and the descendants of white parents 
would perish from the torrid zone long before they could have 
acquired the peculiar skin and the specialities of organization 
suitable to such a climate. 
Moreover, we find a vast variety of strongly-marked types 
amongst such a population as inhabit the British Isles, and 
there is, perhaps, no family of persons that can trace back 
their pedigree for many generations who must not be con- 
strained to admit that some prevalent features of disposition 
or of mental constitution have been manifest in them from 
one generation to another. 
This indestructibility of organization appears to me to be 
irreconcilable with the notions of evolution. The phenomenon 
of atavism, or recurrence to type, deserves especial study in 
this connection. 
In fact, if there is anything which must strike an observer 
in the organized world it is the order and the constancy which 
we see reigning for ages. The cause of all this is simple 
and unique. If we could suppress infecundity between the 
species — suppose that the unions between wild species were 
in all senses and indefinitely fruitful, as they are among our 
doves and in our stables, what would happen ? The barriers 
between species, between genera, would be taken away. 
Crossing would take place in all directions ; everywhere would 
appear intermediate types ; everywhere the actual distinctions 
would gradually become effaced and disappear. It is impos- 
sible to imagine where the confusion would stay its course. 
It would become a chaos of misformed creatures, such as the 
Babylonians dreamt of, and such as Lucretius described. 
“ Infecundity between species in the organic world has consequently as 
important a part as the force of gravity in the celestial world. It maintains 
* See Appendix E. 
Q 
VOL. Xfl. 
