1882.] 
Evolution by Segregation . 
461 
lessen rather than to augment the multiplicity of animal and 
vegetable forms. Hence it will be rather a negative than a 
positive factor in the origin of species, not so much favour- 
ing the origin of new varieties as eliminating those — ex hypo - 
thesi the majority — which are not in harmony with their 
surroundings. 
We may even venture to infer that the variety and rich- 
ness of any flora or fauna will be inversely as the severity of 
the struggle for existence. This is no mere supposition, 
since wherever that struggle is intensified by man, whether 
through his own direCt agency or through his introduction 
into any region or island of foreign plants or animals, the 
immediate result is the extirpation of a number of the indi- 
genous species, and the diminution to that extent of the 
total number of organic forms present on the globe. An 
instance of this kind, in California, is noted and commented 
on by Dr. Behr,* in these words : — “Our original vegetation 
has very little power of resistance. Its very variation is a 
proof of a certain want of vitality, for any more vigorous 
organisation, by superseding the weaker ones, would have 
produced originally the monotony developed at present by 
the immigration of foreign plants.” “ Species,” says Mr. 
Wallace, “ can arise only where there is room for them.” 
This passage is, we submit, a substantial admission that 
variation is greatest where natural selection is least aCtive. 
Instances of a similar kind to that in California are but too 
plentiful. 
The aboriginal flora of St. Helena has been substantially 
extirpated by the introduction of the goat, the pig, the rat, 
and the rabbit, conjointly with certain European weeds. 
Similar causes are at work in Mauritius and its adjacent 
islands, in the Galapagos, &c., and even in such extensive 
regions as the Cape, Australia, and La Plata the native flora 
is being impoverished by the very same cause. The abori- 
ginal birds of the Sandwich Islands will, in another half 
century, be known only from stuffed specimens and from 
plates. 
On the other hand, we never find, so far, that this in- 
tensification of the struggle for existence has led to the 
formation of any new species, better qualified than the ori- 
ginal types to cope with or evade the intruders. The only 
changes in this direction which we perceive are modifications 
of habits, in accordance with new or increased dangers, as 
has repeatedly been observed in the more populous parts of 
the United States. 
* California Rural Press, 
