La evaluación desde el enfoque formativo

Let us examine again some of Lynn Margulis’ views concerning the role of symbiotic systems in generating variation:

,..according to present-day neo-Darwinian evolutionary theory, the only source of novelty is claimed to be by incorporation o f random mutations, by recombination, gene duplication and other DNA arrangements. As is emphasised by those using the term “symbiogenesis”, symbiosis analysis contradicts these assertions by revealing “Lamarckist” cases o f the inheritance o f acquired genomes... The standard textbooks on evolution catechize all species and higher taxa (genera, families, phyla) as having evolved in the same way: by gradual accumulation of favourable mutations. .. Yet not a single example o f the origin o f such lower taxa (species) exists in the literature.

Leaving aside whether or not the specific genetic mechanisms mentioned really are the only ones admissible in neo-Darwinism, let us divide the ideas suggested above into three separate issues. One, the notion that symbiosis provides a means of variation generation beyond mere “random mutation”. Two, that neo-Darwinism insists upon ‘gradualism’ in evolution, and symbiosis provides a means o f the generation of variation which is not ‘gradual’. And third, that symbiosis is in some sense

Michelle Speidel 116

“Lamarckist” . This third question will be dealt with in section 4.4.3, concerning heredity.

Many o f the issues concerning ‘randomness’ were examined in the last chapter, and it was noted there that it is difficult to precisely locate the ‘element of chance’ in evolutionary theory. With no clear means of delineating the precise way in which ‘randomness’ functions in a theory o f evolution with a strong stochastic element, it is not easy to evaluate quite how symbiosis-based approaches are at odds with the idea of variation through random mutations, as neo-Darwinism seems to suggest superficially.

In section 3.2, in the discussion concerning random drift, it was noted that for ‘randomness’ to make any sense at all as an element in evolutionary theory, it must be random with respect to something else. That is, random with respect to some ostensible or observed order in the evolutionary system. And we also saw that neo- Darwinism, as anti-Lamarckist, claims that mutations or adaptations are ‘random’ with respect to adaptive advantage, that is, adaptations do not arise because they will be useful in future, they merely arise ‘randomly’ and are culled by the forces of selection.

We can reconstruct the symbiotic position on randomness in two different ways. One, it could be that symbiosis provides a means o f generation of variation that does not proceed by the gradual accumulation of random mutations or gene recombination. O^two, it may be that symbiosis denies that evolution is random in the sense that symbiosis is Lamarckist in process. If the former is the correct reconstruction, then symbiosis-based approaches must rather be characterised as ‘anti­ gradualist’ rather than simply ‘anti-random’. For what seems to be at issue is the way in which evolution occurs on a phylogenetic level. In the case of the symbiotic origin of eukaryotes, it is clear that for proponents of symbiosis, the way in which eukaryotes formed is, perhaps, ‘saltationalist’ rather than ‘gradualist’, since the symbiotic union of prokaryotes to form the eukaryote cell happened ‘all at once’, and there was no “missing link” in a gradual transformation through the accumulation of piecemeal adaptations between prokaryote and eukaryote.

But there is an important distinction to be made here, for it is not the case that neo-Darwinism depends solely upon random mutation as a characterisation of variation generation; all it requires is that variation be random with respect to advantage And even a symbiotic cooperative innovation does not appear to entail that this innovation be directed, or non-random with respect to advantage. Margulis then perhaps means to

say that evolution happens more quickly if it is characterised by cooperative symbioses, rather than slow mutation. But neo-Darwinism, though it is gradualist, is not gradualist by depending solely on random mutations in the sense of slow changes, but rather through its insistence that variations are not directed by the environment

If symbiosis is ‘anti-gradualist’ then it is not obvious that it is a true challenge to neo-Darwinism.154 For it should be clear that none of the three elements o f neo- Darwinism (natural selection, variation, heredity) are ‘time-indexed’ in any way. Neo- Darwinism does not provide any account o f the rate of evolution in itself. Of course, there has been an enormous amount o f research on the rate o f genetic change in populations, on the macro- and micro-level, with a view to understanding what the general rate o f evolutionary change must be. This information would be immensely valuable in evaluating the time at which species diverged, for instance. But a generalised rate of evolution or even o f mutation rate, has been difficult to find. For example, Maynard Smith reports some of Haldane’s estimates in his Theory o f Evolution. These estimates proceed by assigning a value defined as the “intensity of selection” which is a measure o f how many organisms in a population die because they are less fit than others; this value then can be used to calculate the number of deaths due to poor fitness in terms o f the number of generations that must pass before an unfit trait is supplanted entirely by the fitter trait.155 But these studies simply reference the rate o f evolutionary change under certain conditions, work only for a small number of fitness traits, and are, to some extent, unreliable. There is no suggestion that these seek to provide an account of any underlying rate o f change over time. Symbiosis may, on this account, deny that evolution happens as slowly as neo-Darwinism claims, but it must be conceded that neo-Darwinism in itself has no account o f any privileged time scale fo r evolutionary change.

So if symbiosis is a criticism of gradualism, or neo-Darwinism’s dependence on random mutation as the only source for variation, or if it is an attempt to show that evolution happens more quickly than neo-Darwinism might have it, it is not clear that it could be classed as a challenge to neo-Darwinism o f great importance If it merely queries the time-scale of evolution, and criticises neo-Darwinism’s dependence on

154 Maynard Smith makes a similar point in “A Darwinian View of Symbiosis” in

Symbiosis as a Source o f Evolutionary Innovation: Speciation and Morphogenesis

eds. Lynn Margulis and Rene Fester (Cambridge MA: MIT Press, 1991)p 37-8 155 Maynard Smith, John The Theory o f Evolution p 47, pp 282-5

Michelle Speidel 118 ‘random’ mutation simply as an exemplar o f neo-Darwinism’s inherent ‘gradualism’, then it must be said that neo-Darwinism as a research programme has little to say about the time-scale o f evolution in this sense. If a symbiosis-based research programme’s assumptions have only this to say, then it is perfectly compatible with neo-Darwinism. At best, it might be said to be a sub-research programme, one that may dispute some of the more metaphysical core assumptions of neo-Darwinism (gradualism being perhaps one of them) but agrees with all of the mechanisms which instantiate neo-Darwinism’s conception o f the way in which its three components work together.

O f course, if symbiosis queries neo-Darwinism’s characterisation of variation as ‘random’ for other reasons than the ones outlined above, this may be a more serious challenge. We have seen that ‘random’ ought to be read as ‘random with respect to adaptive advantage’ as a core mechanism o f neo-Darwinism. If symbiosis disputes this particular reading of random, then it contravenes a significant mechanism o f neo- Darwinism, as well as its metaphysical counterpart: that is, it would violate the anti- Lamarckist stricture of random, rather than directed, variation, and violate the anti- teleological metaphysical assumption of neo-Darwinism by allowing variation to occur toward an adaptive goal. This would constitute symbiosis-based research programmes

-form­

as a separate research programme tljan that o f neo-Darwinism.

To return to the quote by Margulis offered above, I want merely to make it clear that there is some difficulty with disputing neo-Darwinism as postulating evolution through the accumulation of random mutations. The difficulty is that this characterisation may mean that neo-Darwinism is gradualist, and symbiosis is then in a sense ‘saltationalist’, or it may mean that neo-Darwinism is anti-Lamarckist, and symbiosis is Lamarckist. Clearly these are different, and the latter is far more o f a challenge than the former The remarks by Margulis perhaps mean to say that symbiotic evolution is ‘saltationalist’ because it makes use of Lamarckist mechanisms such as the inheritance of acquired genomes. If this is correct, then symbiosis is surely a challenge to neo-Darwinism, but now the question must be: Are the mechanisms described by symbiosis truly Lamarckist, do they themselves postulate a different means of heredity that is outlawed by neo-Darwinism, and do they entail teleological evolution?