Investigating Dms from an Adaptive Perspective

Chapter 2 Investigating DMs from an Adaptive Perspective

The previous chapter established that a certain Darwinian perspective was required to investigate DMs’ context-construction function. The current chapter is concerned with the methodology such a perspective entails. But let us begin with an outline of Darwin’s Theory of Evolution (TE), from which the perspective under consideration stems.

2.1 Darwin’s Theory of Evolution

On the Origin of Species by means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life was published in 1859. What is known as Darwin’s theory of evolution (TE) in fact comprises five theories:1 a) ‘Evolution as such’, whereby the “characteristics of lineages of organisms change over time.”2 b) ‘Common descent’, whereby all species diverge from one or a few common ancestors. c) ‘Gradualness’, whereby differences between organisms evolve by small gradual steps through intermediate forms (rather than by leaps or ‘saltations’). d) ‘Population speciation’, whereby “evolution occurs by changes in the proportions of individuals” within a population that differs in one or more hereditary characteristics. (This concept of population evolution also applies to the formation of new species from a common ancestor.) e) ‘Natural selection’,3 whereby a non-random selection process (natural selection) is responsible for the change in the proportions of variant individuals within a species.

In other words, natural selection4 operates within classes of biological entities that differ in one or more characteristics. Within a defined context, this

1 This is based on Futuyma (1998: 21–22). See also Mayr 1982. 2 This is not an original idea of Darwin. 3 This was independently proposed by Wallace (1858). 4 Futuyma (1998: 349) defines natural selection as “any consistent difference in fitness (i.e., survival, reproduction) among phenotypically different biological entities”, which may be

© koninklijke brill nv, leiden, ��6 | doi ��.��63/9789004273818_003 Investigating Dms From An Adaptive Perspective 25 difference results in a difference in ‘fitness’ (i.e., survival and reproduction), in that those endowed with advantageous traits have a better chance to survive and to pass such traits on to the next generation. Consider a species of plant in which the leaves are finely dissected in some individuals but not in others. In a hot region, where finely dissected leaves constitute an advantage, those which possess that feature would be favoured by natural selection over those which do not (Futuyma 1998: 357). A feature which “has become prevalent or is maintained in a population (or species, or clade) because of natural selection for that function” is defined by Futuyma (1998: 355) as an adaptation5 for that function. However, the concept of adaptation is a complex one, and, as Mayr (1983: 325) comments,

The one thing about which modern authors are unanimous about is that adaptation is not teleological, but refers to something produced in the past by natural selection.

A feature that is found to “enhance reproductive success [. . .] relative to other possible features” (Futuyma 1998: 354) may be an adaptation, but it may also be the result of phylogenetic history. Further complications include the fact that while a feature that serves a current function may have originally evolved for that function, it is also possible that it originally evolved for no function at all, or a different function. In which case, following Gould and Vrba (1982), one may want to refer to it as a ‘pre-adaptation’, or an ‘exaptation’, depending on the stage at which it is being considered, that is, before or after it was co-opted for its current function.

2.2 Alternative Theories of Evolution

The Origin of Species encountered much opposition. While evolution by common descent was accepted by most scientists by the 1870s, natural selection was widely rejected until the Evolutionary Synthesis of the 1930s and 1940s. Anti-Darwinian theories included neo-Lamarckism, orthogenetic and mutationist theories. Neo-Lamarckism was based on the belief that characteristics acquired during an organism’s lifetime can be inherited. Orthogenesis

“individual genes (which must have some phenotypically variable property, if they differ consistently in fitness), groups of genes, individual organisms, populations, or taxa, such as a species.” 5 In evolutionary biology, ‘adaptation’ is also used to refer to the “process of becoming adapted” (Futuyma 1998: 354).