Biology Reference
In-Depth Information
light on, the microscopic (i.e., molecular) data on organisms that have been
accumulating in biology over the past one and a half centuries. Just as Newtonian
mechanics failed to account for microscopic observations (e.g., blackbody radia-
tion, atomic line spectra, the photoelectric effect), so it would not be surprising if
Darwin's theory of evolution will be found inadequate to account for certain
molecular data on living systems (e.g., the role of DNA in inheritance and morpho-
genesis, the genetic codes, signal transduction cascades, the cell cycle, cell differ-
entiation, genetic drift, etc.). This is why it is absolutely essential that a microscopic
theory of evolution be constructed that can not only account for molecular data on
living systems but also subsume the Darwinian theory of evolution, just as quantum
mechanics subsumed Newtonian mechanics.
As pointed out by Mayr (1991), Darwin's theory of evolution is not a single
theory but a system of at least four theories:
1. Organisms are not permanent but change in time.
2. Species multiply by branching into daughter species or by forming founder
populations that evolve into new species.
3. Evolutionary changes occur gradually and not by the sudden production of new
individuals belonging to a new species.
4. Evolution occurs through (a) variation of heritable traits and (b) selective
survival of individuals adapted to their environment.
It is probably safe to assume that Items (1) and (2) have been confirmed by
empirical data. Some evolutionary biologists may dispute the validity of Item (3)
based on the theory of punctuated equilibrium (Eldredge and Gould 1972). Apply-
ing the generalized Franck-Condon principle (Sect.
2.2.3
) to evolution, it can be
predicted that phylogenesis (i.e., the evolutionary development of groups of
organisms) will be rate-limited by the speed of geological changes (Ji 1991),
which would be consistent with the idea of punctuated equilibria. Item (4) may
also be viewed as confirmed by empirical data, although the microscopic
mechanisms underlying the variation of heritable traits are still unknown.
Darwin's theory of evolution was constructed in the absence of any knowledge
about (1) how variations of individual characteristics arose and (2) how these
characteristicswere transmitted fromone generation to the next. The so-called
Modern
Evolutionary Synthesis
(Mayr 1991) was formulated between the mid-1930s and
the mid-1940s to fill these lacunae by invoking (1)
random mutations
as the source
of genetic variations and (2) the
Mendelian genetics
as the mechanism of inheritance.
As already pointed out, Darwin's theory of evolution is a
macroscopic
theory
(and to a large extent this is also the case with the Modern Evolutionary Synthesis)
that was formulated at least a century before the full-fledged science of molecular
biology was born with the discovery of DNA as the key molecule of inheritance, as
succinctly summarized by Zimmer (2009):
While Darwin recognized that variation and heredity were the twin engines that made
evolution possible, he did not know what made them possible. It would take almost
a century after the publication of On the Origin of Species for biologists to determine
that the answer was DNA
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