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Another
area of intense debate concerns the primacy of purely ‘Darwinian’ gene-based
natural selection. One important difference between Darwin’s theory and those
which had been proposed before, such Lamarck’s, is the mode of inheritance.
Where Lamarck allowed for the inheritance of characteristics acquired during an
animal’s lifetime, Darwin realised that the inheritance of traits seen in
commercial animal breeding was sufficient to enable natural selection and
evolution. The integration of Mendelian genetics into evolutionary theory in
the 1930s provided a clear endorsement of Darwin’s intuition. Inheritance was
explained in terms of the transfer of genes from parent to offspring, so only
those traits that could be encoded in genes would be preserved. Furthermore,
the ‘central dogma’ of cell biology states that information cannot flow from
the organism to the gene. This means that the only unit of natural selection is
the gene, and in theory the entire ‘epic of evolution’ can be expressed as a
history of changes in gene-frequencies. This account is a triumph of reductionism.
Richard
Dawkins produced a masterful account of evolution in these terms in his 1976
book The Selfish Gene. There have
been ongoing discussions concerning his use of the word ‘selfish,’ but it did
make his message clear: evolution occurs at the level of genes. This dogmatic
understanding of evolution is essential if Darwinian natural selection is to
remain the sole explanation for the
origin and adaptation of species. However, from early on it was clear to Darwin
that selection may occur in other ways as well. The debate over possible
‘levels of selection’ and different kinds of selection is still very much
alive. Conway
Morris goes so far as to say that “claims for the primacy of the gene have
distorted the whole of biology.”
Most
arguments challenging a purely gene-centric view of evolution point to the
Baldwin effect. In 1896 James Mark Baldwin wrote a paper on ‘A New Factor in
Evolution’ arguing that the relationship between environment and organism was
not fully captured by a purely Darwinian explanation. While it is true that
organisms adapt to become fit in a given environment, mobile organisms can seek
out different environments. At a minimum, Baldwin’s proposal suggests that
offspring inherit more than genes from their parents; they also inherit the
environment into which their parents bear them and any disposition they may
have to travel to more favourable environments. In other words, the door is
open for adaptive behaviour to be inherited.
It
is conceivable that behaviours can be encoded in genes, but they can also be
learnt through mimicry. If
learnt behaviours are afforded a role in evolution then we have left the realm
of pure gene-based Darwinism. It is true that Darwin’s mechanism of natural
selection can be expected to operate in any system that has replication,
variation and some measure of fitness. As such, it can be applied to the
development and transmission of behaviours, ideas and culture. But behaviours
and ideas are far more fluid than genes, and the concept of fitness is once again
problematic. Dawkins developed the idea of the ‘meme’ and
attempted to show how Darwinian ideas could be applied to culture, but it has
acquired few advocates.
Darwin
himself came to the conclusion that “Natural Selection has been the main but
not exclusive means of modification.”Ruse represents the current situation as follows: “A Darwinian has to regard
natural selection as the most important evolutionary mechanism that there is. ...
There is disagreement over how important “most important” really is.” The
debate over higher levels and kinds of selection continues, however, it is
likely that we will see the distinction between ‘ultra-Darwinism’ and the
broader concept of evolution grow. It may be that natural selection and Darwin
will come to occupy positions analogous to gravitation and Newton in physics;
i.e. central, but just part of a much larger picture.
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| Feedback | Contributed by: Adrian Wyard
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