Ornithology, Evolution, and Philosophy 123

A Modern Unified Theory of Evolution 219
with them only a very small proportion of the genetic variability of the parent population.
This idea goes back to an early formulation by Rensch (1939: 184) who,
however, did not appreciate its importance. He emphasized (transl.) that “the gene
pool of a few individuals [establishing a new island population] never corresponds
to the total gene pool of the numerous individuals of the parent population. In
such cases the newly developing island race is not characterized by an increase but
byadecreaseofgenes” (italics in the original).
In a later article on “Change of genetic environment and evolution” (which he
considered as one of his most important publications) Mayr (1954c) discussed the
genetic processes during speciation of peripherally isolated founder populations.
His main idea was that in the limited gene pool the selective value of the genes
would be different from the original condition in the parent population particularly
owing to inbreeding and a rise in homozygosity. Later the population will
enlarge and gradually build up its depleted genetic variability. Rapid evolution
in founder populations may lead to the development of strongly differentiated
bizarre peripheral isolates (p. 158). Such forms, however, have low evolutionary
success, when subsequently exposed to competition with mainland stocks. Mayr
did not claim, however, that every founder population speciates, that every genetic
change in a founder population is a genetic revolution or that speciation occurs
only in founder populations. On the other hand, he was already fully aware of the
consequences of his theory pointing out that geographical isolation and the small
size of speciating founder populations may explain the phenomenon of lack of
documentation of speciation in the fossil record.
As he stated, “Many paleontologists have postulated various kinds of typostrophic
‘saltations’ in order to explain the absence of crucial steps from the fossil
record. If these changes have taken place in small peripheral isolated populations,
it would explain why they are not found by paleontologists” (1954c: 210).
Many years later the paleontologists Eldredge and Gould (1972) based their
theory of “punctuated equilibrium” on Mayr’s observations. Although they did
refer to his relevant publications, this intellectual debt got almost lost in later
years. In developing his model of genetic revolutions during the speciation process
Mayr (1954c) applied the “new genetics” of Dobzhansky, Wallace and others who
like Wright emphasized the interaction of genes and their varying selective values
depending on their “genetic environment” or “genetic background.” Mayr (l.c.)
introduced these latter terms which were widely appreciated and applied in discussions
of the integration of the gene pool or of coadaptation among genes (Williams
1966: 59). Mayr got the idea of “genetic reorganization” (or “genetic revolution”) in
peripherally isolated populations when visiting Naples, Italy during the summer
of 1951 and lectured on it already in Oxford during September of that year. At that
time, E.B. Ford asked him to contribute a paper on this topic to a festschrift for
Julian Huxley which only appeared 3 years later. Until then Mayr was “mortally
afraid that someone else would get ahead of me.”
In retrospect Mayr commented on his idea of “genetic revolutions” during
speciation in an interview as follows: “I still think that this is an important idea.
The key thing is that the smaller the population, the more important the chance