170 NATURAL SCIENCE [September 
“The greatest danger,’ writes Dr Wallace, “to a species under new 
and adverse conditions is, that it should not be able to adapt itself 
to them with sufficient rapidity. It is for this reason that, as 
Darwin concludes, new species arise from those which have a large 
population, which occupy a wide area, and which present much varia- 
tion, a combination . . . rarely found except in continental areas.” * 
How far is this hypothesis borne out by facts? As a matter of fact 
the majority of species of a country have not a large population, 
nevertheless many of such species have varied as much as, if not 
more, indeed, than the more gregarious species with large popula- 
tions ; thus, it is easy to think of plants, of which large populations 
exist, generally gregarious, and therefore supplying the primary 
condition supposed to be requisite for natural selection; but the 
remarkable feature about them is that they have never been known 
to vary! Thus, Sir J. D. Hooker gives no varieties whatever to any 
of the following species, Ranunculus ficaria, Caltha palustris, 
Lychnis diurna, Erica cinerea, Bellis perennis, Urtica diorea, Galiwnr 
verum, Scilla nutans, Lemna minor, Pteris aquilina, &. And 
when we cross the channel (though England is really or physically 
part of the Continent) we find no more signs of variation there, 
whether in France, Germany, Switzerland, the Tyrol, &c. 
On the other hand, take an extremely common plant, Polygonwm 
aviculare ; though abundant, it is scarcely a social plant, at least, to 
the extent of those mentioned. It produces several varieties, but 
are they found in the midst of the commonest, say, the roadside 
type? Sir J. D. Hooker says:—“ Var P. littorale (littoral) a 
passage to P. maritimwm (maritime); Var. agrestinum (field 
form); Var. arenastrum (sand-loving form); Var. rurivagum (way- 
side form);” hence these varieties are not found in the midst of 
the commonest form, but away from it, in localities characterised 
by special physical features. In other words, these varieties arise 
by self-adaptation to their special environments, respectively. 
The second condition requisite for variations consists of “ changed 
conditions of life.’ Both Darwin and Dr Wallace admit that “a 
change of climate and food” is requisite for a new variety to arise 
among the parent type. The latter writer says:—“ Now let some 
important change occur, either in climate, in abundance of food, or 
by the irruption of some new and hitherto unknown enemies, a 
change which at first injuriously affects the species.”? Similarly 
Darwin writes :—‘“ Let the external conditions of the country alter,” 
and again, “take the case of a country undergoing some .. . change.” 
The question at once arises, where and when do we find these - 
changes occurring in, or coming to, any particular district, where 
some species with a large population happens to be? Is nature 
1 Loe. cit., p. 484. 2 Loe. cit., p. 483. 3 “Origin, etc.,” p. 68: 
