GEORGE FORSTER. IoI 
more easily effected, and more often produce fertile off- 
spring than the unquestionably rarer crosses of species 
the frequent failure of crosses between species com- 
pletely accords with the modification of species in the 
lapse of time, as shown above. Provisionally, let us 
hold nothing to be established but that, as to fertility 
and the capability of persistent reproduction, the 
conditions of mongrels and of hybrids are essentially 
similar and differ only in degree, and that on these 
properties, no closer definition or limitation can be 
founded. 
If the older definitions of species go back to Paradise, 
and derive existent species lineally from ancestral pro- 
genitors, miraculously created from the first and never 
modified, the ingenuous statements of Linnzus show that 
all this was accepted as self-evident, and that no thought 
was given to the proof, which would indeed have been 
impossible to obtain. A letter from George Forster to 
Peter Camper, dated May 7th, 1787, proves however 
that, even in the last century, the voices of more far- 
sighted naturalists were raised against this superficial 
treatment of the idea of species. Systems, he said, were 
founded on this idea, yet everything was uncertain as 
long as this expression was not irremovably fixed. But 
hitherto all definitions of this word were hypothetical, 
and in themselves anything but clear. If we are to 
accept aS many species as were created, how is a 
created species to be distinguished from one produced 
by the intermixture of several others? To fall back 
upon the Creation is to lose oneself in the Infinite 
and the Impalpable. “This will never enable us to 
understand anything ; and definitions which rest on an 
