December 12, 2008 | David F. Coppedge

Evolutionary Mutualism Flutters

A story on Science Daily is decorated with a butterfly collection.  Amazonian butterflies studied by an international team were chosen to test Darwin’s theory of mutualism – a kind of symbiosis in which two species benefit one another.  The test yielded a surprise.
    The idea going in was that sister species would evolve apart so as to minimize competition for scarce resources.  The work showed a surprise, however: “The work shows that some species of butterfly that live alongside one another have evolved in ways that, surprisingly, benefit both species.”  One would think they would separate or else compete.

However, this is not always the case.  The researchers show that butterfly species that have evolved similar wing patterns – which act as a warning to predators that they are poisonous – are often not evolutionarily close to each other.  Thus the similarity is not due to shared ancestry but is an evolutionary adaptation.  The similar pattern benefits both species, as predators will only need to learn once to avoid the signal – ‘learn’, in this context, being a euphemism for eating a poisonous butterfly.

Some of the unrelated species share the same habitat and fly at the same height, for example.  Instead of competing, they share the benefits of similar looks, the article said.  “The new paper shows that issues other than pure competition, such as protection from predators, can play an important role in evolution.” The scientists expected that the mimicry would pay benefits to the tasty species, but did not expect that both species would live alongside each other.

One can look at this story as a success for Darwin or a defeat for Darwin.  It provided an evolutionary explanation for an observation, but then again, it surprised the scientists.  That is why Darwin’s theory is so successful.  His idea allows for any data, even data opposite what was expected, to score points for the theory.
    The finding seems very un-Darwinian.  What happened to survival of the fittest?  Are they saying that two unrelated species in the same niche are equally fit?  What would Malthus think?  The scientists also failed to explain exactly how two unrelated species converged on the same patterns and behaviors.  Given such a bad track record, we won’t assume they know what relatedness means.

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Categories: Terrestrial Zoology

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