Science for University Students. Part II. Translations. Сологуб Л.И. - 48 стр.

UptoLike

ВУЗ: 

СГАУ | Самара

Составители: 

Рубрика: 

evolution. Recently, many evolutionists (particularly developmental biologists
and paleontologists) have rejected neo-Darwinism as a universal guide for
studying evolution, finding its recognition of only a single important level of
causality too restrictive. Macroevolutionary trends and novelties are investigated
alternatively as the product of multiple, hierarchically organized causal forces
that act at the genic, organismal, and species levels. Historical processes
producing differential speciation and extinction among lineages on a geological
time scale augment population-genetic processes as important causes of
evolution. The higher-level processes may oppose and thereby cancel or reverse
the effects of population genetic processes. Conflict between the neo-Darwinian
and hierarchical theories has split evolutionary biology. Levinton seeks to
reunify the field by introducing some explicitly hierarchical elements into neo-
Darwinism while retaining natural selection as the primary cause of organismal
evolution.
Developmental biology has challenged neo-Darwinism repeatedly from the
work of Richard Goldschmidt to the currently popular theories of epigenesis. I
found Levinton’s discussion of Goldschmidt particularly insightful. Levinton
shows that Goldschmidt argued simultaneously the now-discredited notion that
higher taxa originate via special chromosomal mutations that produce aberrant
“hopeful monsters” and the substantive position that developmental processes
mediate gene expression and evolutionary directionality. The latter claim
underlies recent structuralist epigenetic theories that attribute a large component
of evolutionary directionality to constraints imposed by developmental
processes rather than to natural selection. Saltational origin of novel structures is
seen to result from the response of a developmental process to genetic
perturbations that affect early ontogenetic stages. Levinton’s theory includes an
important evolutionary role for developmentally mediated constraints and
discontinuities, but it remains firmly within the neo-Darwinian tradition by
asserting that the alternative, complex phenotypes subject to developmental
regulation are built gradually by natural selection and then tied to genetic
switches that allow them to be suppressed and reactivated. Genetic switching is
said to produce a false appearance of saltatory origin for key features. Levinton
thereby rejects, in favor of population genetic mechanisms, the structuralist
notion that generative processes intrinsic to organismal development can
determine evolutionary novelties and trends.
Levinton acknowledges a role for evolutionary processes that transcend the
species level in generating dominance patterns among taxa, but he maintains that
no processes of differential speciation and extinction have assembled complex
adaptations. He is particularly critical of punctuated equilibrium, which
proposes that species maintain static morphologies that are disrupted only during
infrequent events of branching speciation. Punctuated equilibrium views
accumulated speciation rather than accumulated intraspecific evolution as the
primary source of morphological change. Levinton accepts the phenomenon of
47

Страницы