MUTATIONS 
The most brilliant contribution to the species problem has 
been the outcome of transferring the search for the cause of 
variation into an investigation of the factors responsible for 
the uniformity of individuals of successive generations. Out 
of this development of modern genetics has come not only a 
localization in the reproductive cells of the mechanism by 
which hereditary similarities are achieved, but an assurance 
that the inception of new species must take place in those 
same genes and a considerable acquaintance with the potenti- 
alities of genes. 
These laboratory studies have always led to the conclusion 
that changes in genes occur in sudden jumps, sometimes of 
small degree, sometimes of considerable size, but always as 
mutations which are complete as soon as they have occurred. 
This concept has been held in contrast with the neo-Darwinian 
conception of “fluctuating variations’’ which, by being ac- 
cumulated over many generations and bent in a given direc- 
tion by the force of natural selection, would gradually give 
rise to the characters of new species. Under this latter in- 
terpretation there may be incipient species of the sort con- 
ceived by many taxonomists in their definitions of varieties 
and subspecies; under the genetic interpretation the first 
mutant individual embodies all that the new species will con- 
tain, and is the new species as soon as it is given an oppor- 
tunity to perpetuate its mutant characters thru a population 
of individuals. 
The genetics data are conclusive as to the frequent occur- 
ence of mutations in the laboratory; there are numerous 
records of the appearance of similarly mutant individuals in 
nature, but there is little satisfactory evidence that these are 
the individuals out of which new species are made. Perhaps 
the best body of proof is that of Crampton’s (1909-1928) on 
the development of geographically isolated races of snails 
from mutant stocks in various Pacific Islands. In the tax- 
onomic literature there are a few other suggestions of 
similarly mutant origins of existent species, but such an ex- 
perienced field worker as Chapman is quoted (H. F. Osborn, 
1926) as finding among the birds next to no species which 
might be interpreted as owing their origin to mutation. 
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