Evolution: Parallel lives

Kevin Padhian in Nature:

LizNevertheless, Improbable Destinies is deep, broad, brilliant and thought-provoking. Losos explores the meaning of terms such as fate, chance, convergence and contingency in evolution. Why do similar solutions — morphological, genetic and molecular — crop up again and again? He became intrigued by these questions when, as a student, he began to study the Caribbean Anolislizards, following groundbreaking work by ecologist Thomas Schoener. These lizards inhabit a great range of island sizes and habitats, and tend to evolve similar adaptations and roles in similar circumstances. However, species on different islands that resemble each other aren't each other's closest relatives. Why not?

The answer, we think, is that closely related lineages have similar genetic components, so under comparable ecological conditions they are likely to produce similar mutations that are then selected for. Many call this convergence; I prefer the term parallelism for closely related lineages. 'Convergence' is appropriate for reinvention in very different groups — the superficially similar wings of birds and pterosaurs, or the elongated grub-seeking fingers of the aye-aye (Daubentonia madagascariensis) and striped possum (Dactylopsila trivirgata). We can catalogue examples all day, but is there any real theory of convergence? We cannot assert that some lineages are 'fated' to converge on these features. Biological ideas of determinism went out with Jean-Baptiste Lamarck in the late eighteenth century. Evidence against determinism is the prevalence of creatures whose adaptations have never been duplicated: the kangaroo, the platypus (Ornithorhynchus anatinus), the century plant (Agave americana, which blooms only once in its multidecade life) — and humans. Primates have the equipment apparently needed to evolve flight: arboreal habits, large brains, good coordination and active metabolisms. Yet no primate seems to have evolved gliding, let alone powered flight. No evolutionary duplication is inevitable.

More here.

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