Universal convergence

Convergence is by no means restricted to such seemingly “engineered” solutions as camera eyes, but is actually ubiquitous, as the forces of selection can lead unrelated organisms living in similar situations to acquire remarkably similar adaptive traits in response. Literally the solutions range from molecules to societies, from echolocation to walking.

Carbonic anhydrase tructure graphicRegarding molecular convergence, we would be deeply suspicious if for example we came across proteins in unrelated animals with exactly the same amino acid sequences, as the number of possible alternative arrangements of the 20 amino acids (or 21 including selenocysteine) in any given protein is gigantic. However, we don’t see that but rather molecular convergences are identified at the level of active sites, reaction mechanisms or other biochemical and structural properties. Consider one of life’s key enzymes, carbonic anhydrase. Because it serves to hydrate (that is add a molecule of water to) carbon dioxide this enzyme is absolutely central to carbon based life-forms, being crucial in such roles as respiration and photosynthesis. Carbonic anhydrase is so important in fact, that one might reasonably predict that its appearance must date back to the very dawn of life, and so be inherited by all subsequent organisms. This is not the case: carbonic anhydrase is rampantly convergent and has evolved independently at least five (and maybe six) times.

Big-eared Townsend bat photoThe ability of bats to sense their world using echolocation is now well known, but during the Second World War it was assumed that there had been a major security leak when scientists were found eagerly chatting about their new discoveries in bats and it was assumed they had somehow found out about the top-secret sonar. In addition to the evolution of sound-based detection systems in bats and the invention of sonar by humans, sonar has evolved convergently not only in whales and dolphins but even in birds, where it has actually appeared at least three times.

What about locomotion? You run after a cockroach, and it in turn flees. Two legs pound after six legs, but did you know that the mechanics of running and the underlying neural networks are strongly convergent between you the mammal, and the cockroach the insect? So striking is this convergence that it is now being used to help design robots.

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