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of preservation, and those scorpions are hardly distinguishable from 
such as now live. . . . Close scrutiny is needed in order to 
distinguish them from living scorpions.” 
These instances, culled from Mr. Huxley’s New York 
Lectures on Evolution, amply suffice to illustrate the prin 
ciple that some species remain unaltered from age to age. 
We may, then, accept the long-continued stability of 
species as an undoubted fact, and proceed at once to con 
sider what explanation can be given of this phenomenon. 
In the first place, it may be surmised that species some 
times remain unchanged because the external conditions 
remain essentially unmodified. We must remember that 
the transmutation of a species implies that that species 
is already in existence ; that it has been adapted to the 
conditions of life by which it has been surrounded ; and 
that a change of external conditions to which it is neces 
sary that the species should be adapted is, in many cases, 
though not in all, the occasion, if not the cause, of the 
transmutation. If this view be correct, the fixity of some 
species implies that the outward conditions of life have 
remained unaltered or so little altered as not to affect 
the correlation between the organism and the conditions 
among which it lives and moves and has its being. If the 
flora and fauna of Egypt have remained unaltered during 
the last six thousand years, so also, we have every reason 
to believe, has the climate. 
It should, however, be observed that, in order to account 
for the stability of species, it is not absolutely necessary to 
assume that the climate of any one spot on earth has 
remained unchanged during the geological ages. We have 
only to suppose that certain species have migrated from a 
sphere which has become unsuitable to them, and have 
found another to which they are already adapted. During 
successive glacial periods it is certain that many species