The Problems of Evolution by Mark Ridley





revisiting an old reference

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This
recommended reading for my biology class a couple of decades ago is sometimes a
crisp and fair summary of why evolution is the powerful theory that it is.
Discussion is a little convoluted in places and use of terminology and
discursive argument does not aid comprehension by a less expert reader. The
index is good and, while the further reading could now be considered dated, the
nominated authors are really timeless pillars of evolutionary biology that
deserve inclusion. Overall, this is a partly out of date introduction to
evolution that aims more to tick the boxes on areas of one-time controversy than
to explain them simply. It is an interesting reminder of how popular science
writing, including by this author, has leaped ahead in the last couple of
decades. Certainly better introductions now exist. It was not always an easy
read but my comments follow.

A succinct and logical comparison with
creationism and transformism lays the foundation for a discussion on heredity
and the mechanism of evolution. Some aspects, such as the story of Mendel's
peas, may be well known to the reader and are easily skimmed. Their inclusion
remains important to mount the overall case.

Introducing the mechanisms
of evolution, the water gets a little muddy. Ridley spends some time extracting
the theory of evolution from charges of tautology made due to the maxim of
"survival of the fittest". In explaining the gradual evolution of complex eye
function (p 34), one mechanism, "symbiosis", is characterised as where "the
parts of a complex organ evolve separately, in different species, and are only
put together later, when many of the parts have been separately perfected". I
trust this fundamental misunderstanding of speciation and, for that matter of
the direction of evolution as previously defined in the text, is an editing
error. When the proposed mechanism of symbiosis is explained, reference is
properly made to the Margulis theory of cellular evolution, but further
reference back to the putative example of the complex eye is omitted. In a
scholarly text, this confusion is a head-shaker for me and the factual error to
be condemned.

In describing `Natural Selection in Action', Ridley works
around selection at the gene level, showing why group selection probably will
not work. This book was written before Dawkins's popularisation of the selfish
gene theory - as a result it is less confident and clear in its expression.
There is less excuse for the prosaic discussion of evolutionary constraint
because an robust and elegant debate had occurred on this issue, such as through
Gould and Lewontin's `Spandrels of San Marco ...', and which provided clear and
unambiguous language from which the author could postulate.

Thirty
years after publication, it is not surprising that the chapter `Molecular
Evolution' is dated. Today the extrapolation of the molecular theories of
neutralism and selectionism is less relevant, in fact the next chapter on the
`Principles of Classification' sets the scene for developments since this book
was published. Navel-gazing comparisons between phenetic and phylogenetic
classification have been overtaken by the power of genomics and computing. The
discussion of cladism is important historically, although none of these issues
now cause the level of `problem' they did earlier.

The key phenomenon of
speciation is introduced with the problem of the reproductive and morphological
concepts and concludes that both are real and not necessarily competing. Then
the adaptive and gene flow mechanisms of speciation are posited with the
conclusion that both are relevant but to uncertain extents. I felt that this
chapter could have been argued in more direct language and the reader would then
be allowed a clearer take-home message. The second chapter on speciation
assesses sympatric and allopatric speciation and the arguments against the
former. The arguments were generally sound with the possible exception of why
natural selection works against hybrid and heterozygous forms. I looked forward
to this explanation but the example offered seemed simplistic and
artificial.

`The Rates of Evolution' is a comparison of gradualism and
punctuated equilibria. The facts are covered and I expect macro-mutations would
be explained more clearly now due to the progress in molecular genetics. In the
chapter `Macro-evolution', Ridley notes that many arguments, for example that
favouring faster evolution of larger animals, can be weak. Certainly basing an
argument on the contention that modern marsupials are larger than their
ancestors needs to consider the Australian megafauna which became extinct in the
last 100 000 years - I became very sceptical about any case based on that
example.