Две теории биологической эволюции. Гродницкий Д.Л. - 129 стр.

UptoLike

ВУЗ: 

СФУ | Красноярск

Составители: 

Рубрика: 

stopped reproducing bisexually (Maynard Smith 1983). Moreover, the only experi
ment that resulted in the origin of a taxon reproductively isolated from its parental
population was conducted on organisms reproducing parthenogenetically without
meiosis, i. e. in the absence of or at drastically reduced recombination of genes
(Shaposhnikov 1961, 1965, 1966).
Third, the synthetic theory predicts that evolution is impossible, when a popu
lation is deprived of hidden genetic variation. Therefore, haploid organisms should not
evolve or only extremely slowly evolve (Rasnitsyn 1980). All mutations in haploid
organisms are immediately expressed phenotypically. Since mutations are usually
deleterious, mutant individuals should not mate; their genotypes cannot offer suffi
cient genic material for recombination. Thus, natural selection is deprived of oppor
tunity to transform deleterious recessive mutations into new useful dominant genes.
Nonetheless, insects in which one sex is haploid (e. g. hymenopterans) have under
gone no less intensive evolution than the taxa in which both sexes are diploid.
Fourth, according to the synthetic theory, any isolated population must eventu
ally evolve into a new taxon, since the absence of gene flow from adjacent populations
enable mutation and recombination to generate unique genotypes. Because no two
absolutely identical environments exist on earth, the character of natural selection
also differs in different geographic locations. Hence, growth of genetic barriers to
reproduction is just a question of time (Maynard Smith 1958). However, isolation is
neither necessary nor sufficient for speciation. On one hand, neighboring populations
are known that do not mix although are well able to cross in experimental conditions
(see the «area effect» in Cain & Currey 1963). On the other, many populations sep
arated by the continental drift more than 80 mln yr ago still belong to the same
species (Rasnitsyn, 1987).
Fifth, fluctuations of population density must be followed by evolutionary events
(TimofeeffRessovsky et al 1977; Vorontsov 1980). Mass outbreaks should provide
excellent conditions for action of all neoDarwinian factors of evolution: almost all
individuals survive as population density increases, next all the generated genetic
diversity is subject to catastrophic selection. That is why it looks unusual, from the
viewpoint of the synthetic theory that no evolutionary significant changes have been
reported for species exhibiting periodical mass outbreaks (Rasnitsyn, 1987), the
more so that many economically important species have been intensively studied
through decades and even centuries.
Sixth, following from neoDarwinian axioms, a species cannot originate twice,
owing to randomness of the processes generating new genes and their combinations.
By contrast, several species of domestic plants were first selected by man in the pre
historic time, so that the ancestors of these species remained unknown. In our era,
these species were again «resynthesized» by means of hybridization of certain wild
plants (Dobzhansky 1951). Even the assumption that mutation is a constrained
process cannot explain how it would be possible to generate a copy of the genome of
the previously existing domestic plants from the genomes of their probable ancestors
after hundreds and thousands generations of allopatric life. An analogous result was
SUMMARY
130

Страницы