Endosymbiosis and its implications for evolutionary theory

Abstract

Historically, conceptualizations of symbiosis and endosymbiosis have been pitted against Darwinian or neo-Darwinian evolutionary theory. In more recent times, Lynn Margulis has argued vigorously along these lines. However, there are only shallow grounds for finding Darwinian concepts or population genetic theory incompatible with endosymbiosis. But is population genetics sufficiently explanatory of endosymbiosis and its role in evolution? Population genetics "follows" genes, is replication-centric, and is concerned with vertically consistent genetic lineages. It may also have explanatory limitations with regard to macroevolution. Even so, asking whether population genetics explains endosymbiosis may have the question the wrong way around. We should instead be asking how explanatory of evolution endosymbiosis is, and exactly which features of evolution it might be explaining. This paper will discuss how metabolic innovations associated with endosymbioses can drive evolution and thus provide an explanatory account of important episodes in the history of life. Metabolic explanations are both proximate and ultimate, in the same way genetic explanations are. Endosymbioses, therefore, point evolutionary biology toward an important dimension of evolutionary explanation.endosymbiosis | evolutionary theory | macroevolution | eukaryogenesis | metabolism M any historical accounts have viewed organelle-producing endosymbioses and symbioses in general as competing conceptually against standard evolutionary theory. Although there are several older claims to this effect, I will focus on Lynn Margulis's conjectures about how endosymbioses can be interpreted as posing problems for neo-Darwinian evolutionary theory. My aim is to assess whether endosymbiosis does in fact put pressure on evolutionary biologists and philosophers of evolution to expand beyond gene frequencies and encompass alternative explanatory frameworks.Rather than agents of revolution bent on overthrowing evolutionary theory, it is more likely that endosymbiotic relationships offer their greatest explanatory value as model systems for macroevolution. Such systems can tell us a great deal about conflict and control dynamics in ongoing organismal interactions. They provide remarkable examples of enduring evolutionary game-changing mutualistic relationships, and call out for an account of why such relationships persist and become increasingly stable.However, instead of focusing on "informational" properties of organisms, endosymbiotic systems draw attention to metabolism as a central organizing feature of life. A metabolic perspective focuses explanatorily on biochemical networks rather than genes, on phenotypic interactions rather than informational inheritance, on communities in addition to isolated organisms and lineages, and on major diversifications in the history of life. "Endosymbiotic" views of evolution are therefore valuable for expanding evolutionary explanations, even if they do not constitute a fullblown theoretical alternative to standard evolutionary...

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