Reviews.



303



It is impossible in a short review to deal in detail with a

book so abounding in facts and of so controversial a nature.

Its main themes are as follows:—


(1) That great as is the power of Natural Selection it cannot


originate varieties, but must use and perfect those varia¬

tions which arise.


(2) That there is a limit to the perfecting power of Natural


Selection, since, as soon as a variety is sufficiently ‘pro¬

tectively’ coloured to escape its pursuers, Natural Selection

cannot go on perfecting it in the minute particulars in

which such resemblances are often found, as, for instance,

in the case of a Kallima butterfly, which mimics a dead leaf

even to the venations and possibly also the fungus spots !


(3) That Natural Selection cannot perfect or eliminate varieties


when they are as yet too slight to be of any service or

harm to the individual.


(4) That variations tend to be correlated, that is to say, two or


more variations tend to be inherited together, so that

Natural Selection in perfecting one variety may, at the

same time be permitting other varieties (provided they are

not harmful) to persist. Hence varieties may develop

which are of no special utilitarian or other service to the

animal.


(5) That‘to prey or be preyed upon,’ which are usually con¬


sidered the chief factors through which Natural Selection

acts, are only one of the several causes leading to the

limitation in the numbers of any particular species.

The authors point out that isolation, climate, food supply,

and so forth, have a much more limiting effect than is

generally allowed, and if this be so it seems doubtful if

the colouration of many animals is due to the modifying

action of Natural Selection.


Only two new suggestions or ideas are brought forward,

neither of which, in the writer’s opinion, seem to bear much

weight.


The first is that inheritance may be due to what is termed

‘Biological Molecules.’ For instance, there is supposed to be a

Biological Molecule of colour made up of atoms, each of which



