in's works he would
have found that, when thus extended, the principle of natural selection
is bound to work in favour of the co-operative instincts in the case of
so highly social an animal as man; and that of these instincts
conscience is the highest imaginable exhibition.

[30] For cases, see _Animal Intelligence_, in the chapters on Ants
and Bees; and, for discussion of principles, _Mental Evolution in
Animals_, in the chapters on Instinct.

What I have called tribal fitness--in contradistinction to individual
fitness--begins with the family, developes in the community (herd, hive,
clan, &c.), and usually ends with the limits of the species. On the one
hand, however, it is but seldom that it extends so far as to embrace the
entire species; while, on the other hand, it may in some cases, and as
it were sporadically, extend beyond the species. In these latter cases
members of different species mutually assist one another, whether in the
way of what is called symbiosis, or in a variety of other ways which I
need not wait to mention. For the only point which I now desire to make
clear is, that all cases of mutual aid or co-operation, whether within
or beyond the limits of species, are cases which fall under the
explanatory sweep of the Darwinian theory[31].

[31] Prince Kropotkin in the _Nineteenth Century_ (Feb. 1888, Apr.
1891) has adduced a large and interesting body of facts, showing the
great prevalence of the principle of co-operation in organic
nature.

* * * * *

Another important point to notice is, that it constitutes no part of the
theory of natural selection to suppose that survival of the fittest must
invariably lead to _improvement_ of type, in the sense of superior
organization. On the contrary, if from change of habits or conditions of
life an organic type ceases to have any use for previously useful
organs, natural selection will not only allow these organs in successive
generations to deteriorate--by no longer placing any selective premium
upon their maintenance--but may even proceed to assist the agencies
engaged in their destruction. For, being now useless, they may become
even deleterious, by absorbing nutriment, causing weight, occupying
space, &c., without conferring any compensating benefit. Thus we can
understand why it is that parasites, for example, present the phenomena
of what is called _degeneration_, i. e. showing by their who