The Making of Species 
ditions are comparatively uniform, nevertheless 
it boasts of no fewer than fifteen out of the thirty- 
seven known species of cormorant. A possible 
explanation of this phenomenon may be found 
in the comparatively easy conditions under which 
cormorants live in New Zealand.t| Under such 
circumstances mutants may be permitted by 
natural selection to survive, whereas in other 
parts of the world such mutants have not been 
able to hold their own. 
Prof. Bateson has likened natural selection 
to a competitive examination to which every 
organism must submit. The penalty for failure 
is immediate death. The standard of the ex- 
amination may vary with the locality. 
Isolation, then, is a very important factor in 
the making of species, for without it, in some 
form, the multiplication of species is impossible. 
Let us, in conclusion, briefly summarise what 
we now know of the method in which new species 
are made. We have studied the various factors 
of evolution—variation and correlation, heredity, 
natural selection, sexual selection, and the other 
kinds of isolation. How do these combine to bring 
new species into being, and to establish the same? 
Let us first consider the factor known as 
natural selection, since this is the one on which 
1 Hutton and Drummond record other examples of this in the 
valuable work entitled The Anzmals of New Zealand. 
382 
