Аннотация
H E N a species occupies a very large territory, local differentiation is usually
noticeable in the form of geographical races. Each race may in turn consist
of numerous colonies which are differentiated to a less noticeable extent. The
underlying differentiation in genetic constitution may reflect the local differences
of selective pattern or may be the results of chance occurrence of different mutant
genes, but these factors cannot act effectively unless some sort of isolation ensures
the accumulation of genetic differences.
It is well known that existence of geographical barriers greatly favors the for-
mation of races and new species. However, even if such barriers do not exist, the
large size of the whole area as compared with the migration distance of an indi-
vidual may prevent the species from forming a single panmictic unit, and this
will produce a sort of isolation which WRIGHT
called “isolation by distance”
(WRIGHT 1943). He proposed a model of population structure in which a popula-
tion is distributed uniformly over a large territory, but the parents of any given
individual are drawn from a small surrounding region. He studied, by his method
of path coefficients, the pattern of change in the inbreeding coefficient of sub-
groups relative to a larger population in which they are contained (WRIGHT
1940, 1943, 1946, 195 1 ) . The problem of local differentiation may also be studied
(1948,
in terms of change in correlation with distance as considered by MAL~COT
1955, 1959) ; individuals living nearby tend to be more alike than those living
far apart. In the mathematical theory of population genetics, the problem of local
differentiation of gene frequencies in a structured population is one of the most
intricate, and so far the main results are due to these two authors.
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