Blute Blog

Blute's blog about evolutionary theory: biological, sociocultural and gene-culture.

Twelve evolutionary myths

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1) “Evolution equals mutation plus selection.” This is wrong on both counts. It would be more accurate to say that it equals hereditary innovation, selection and drift. There are forms of heredity other than the genetic including the epigenetic, behavioural, ecological and cultural for example. Even with genetic inheritance, in sexually reproducing species, including most familiar animals and plants, genetic recombination rather than mutation is the source of most hereditary innovations. Natural selection (roughly differences in the ability to survive and/or reproduce based on hereditary differences) is important, but so too is “drift” – the evolutionary term for sampling error, essentially accidents. Just as when tossing a fair coin, in a large number of tosses we expect an equal number of heads and tails but not so in every small group or short sequence of such. In finite populations (and no population is infinite in size), organisms do not always get what they would otherwise. Nature does throw dice.

2) “Mutations are random.” At best ambiguous, depending upon what is meant by random. As used in evolutionary theory, random does not mean uncaused, necessarily unique, or equiprobable. There are many known causes of mutations including ionizing radiation, some chemicals and some viruses for example. Mutations are often a recurrent affair – to the extent that the mutation rate from one version of a gene to another can sometimes balance selection acting against the latter, maintaining an otherwise maladaptive alternative in a population. All possible mutations are not equally probable – “forward” mutations from one version of a gene to another and “backward” ones, their reverse, often occur at different rates. If it does not mean uncaused, necessarily unique, or equiprobable, then what does it mean? As Donald Campbell made clear, the term “random” is ill-chosen. All it means is “blind” or “non-prescient”. On a statistical basis, mutations are not necessarily oriented in an adaptive direction. Most, in fact, are harmful. None of this should be taken to imply that mutation rates cannot be selected and evolve which they can and do in some cases.

3) “Lamarckian inheritance (the inheritance of acquired characteristics) has been proved false.” Not so. If a cell doubles in size and divides once, however the material is distributed among the two offspring cells, 50% of that material was acquired rather than inherited by the parental cell. Lamarckian inheritance then can be half the story. What is false is the theory of Lamarckian evolution – that acquired adaptations, as a result of “use” for example, are preferentially inherited over acquired maladaptations, as a result of “disuse” for example, which, if true, would be miraculous – a skyhook rather than a crane in Daniel Dennett’s memorable terms.

4) “Natural selection causes change in populations.” Not exclusively so. Natural selection can cause change in a population, but it can also maintain stability by selecting against new extremes. There is a story about the views of Charles Darwin and Herbert Spencer on this point. When Darwin read Malthus on over population, the penny dropped and he inferred that the resulting struggle could be the force causing species to change. (He had long believed that they do, in fact, change.) Spencer read Malthus too, but he inferred that the struggle resulting from over population could be the force maintaining the stability of species. When Darwin eventually published his theory, Spencer was chagrined that he had not thought of Darwin’s idea himself. But Spencer had not actually been wrong! Both are possible! Not only can selection cause directional change or maintain stability, but it can also drive wedges in populations splitting them apart as Darwin himself emphasized. After a long hiatus in which it was believed that only geographical isolation could do that, contemporary theory and empirical research now support Darwin’s view.

5) “Evolution equals survival of the fittest.” Only part of the story. Reproduction and not just survival matters. “What matters in evolution is reproduction.”Also only part of the story. In fact, modellers have shown that there is no single definition of “fitness” suitable to all types of populations – with overlapping as well as discrete generations, sexual as well as asexual, with different kinds of life histories, for declining as well as growing populations etc.

6) “Population genetics or the genetical theory of evolution is a complete theory of evolution.” Opinions on this differ as even a cursory review of the macro-evolution and evo-devo literatures reveal, but even confining ourselves to microevolution, I think not. The unification of Mendel’s theory of heredity and Darwin’s theory of evolution which defines evolution as a change in gene frequencies in a population (commonly known as neo-Darwinism in Britain or the synthetic theory of evolution in America and built mainly by Ronald Fisher, J.B.S. Haldane and Sewall Wright in the 1930’s), was a towering intellectual achievement which continues to be refined to this day. However, its elegant simplicity comes at a cost in that while it unifies genetics and evolution, it omits development and ecology. Ideally, a ‘new’ new evolutionary synthesis will be one including not only evolution and heredity, but also development and ecology. I for example have suggested that rather than defining evolutionary change as “a change in gene frequencies in a population”, it be defined as “any change in the inductive control of development (whether morphological, physiological or behavioural) by ecology and/or the construction of ecology by development which results in a change in the frequency of hereditary (including genetical) elements in a population.” As well as including development and ecology, this definition incorporates the cases of both old genes in new environments and new genes in old environments respectively.

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Written by Marion Blute

August 16, 2010 at 1:31 pm

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