_On the state of Development of Ancient Forms._--There has been much
discussion whether recent forms are more highly developed than ancient. I
will not here enter on this subject, for naturalists have not as yet
defined to each other's satisfaction what is meant by high and low forms.
The best definition probably is, that the higher forms have their organs
more distinctly specialised for different functions; and as such division
of physiological labour seems to be an advantage to each being, natural
selection will constantly tend in so far to make the later and more
modified forms higher than their early progenitors, or than the slightly
modified descendants of such progenitors. In a more general sense the {337}
more recent forms must, on my theory, be higher than the more ancient; for
each new species is formed by having had some advantage in the struggle for
life over other and preceding forms. If under a nearly similar climate, the
eocene inhabitants of one quarter of the world were put into competition
with the existing inhabitants of the same or some other quarter, the eocene
fauna or flora would certainly be beaten and exterminated; as would a
secondary fauna by an eocene, and a palaeozoic fauna by a secondary fauna. I
do not doubt that this process of improvement has affected in a marked and
sensible manner the organisation of the more recent and victorious forms of
life, in comparison with the ancient and beaten forms; but I can see no way
of testing this sort of progress. Crustaceans, for instance, not the
highest in their own class, may have beaten the highest molluscs. From the
extraordinary manner in which European productions have recently spread
over New Zealand, and have seized on places which must have been previously
occupied, we may believe, if all the animals and plants of Great Britain
were set free in New Zealand, that in the course of time a multitude of
British forms would become thoroughly naturalized there, and would
exterminate many of the natives. On the other hand, from what we see now
occurring in New Zealand, and from hardly a single inhabitant of the
southern hemisphere having become wild in any part of Europe, we may doubt,
if all the productions of New Zealand were set free in Great Britain,
whether any considerable number would be enabled to seize on places now
occupied by our native plants and animals. Under this point of view, the
productions of Great Britain may be said to be higher tha