Commensalism is a relationship between organisms in which one organism benefits and the other is unaffected. Today’s Daily (pseudo)Science Update – Bacteria Share Light Spectrum with Plant Leaves – boils down to Mr Thomas asserting that such a relationship could not have evolved.

Chlorophyll absorbtion spectra

The specific example is a paper called Microbial rhodopsins on leaf surfaces of terrestrial plants which found that Microbes that live on leaves and which use light to power proton pumps tend to use those that plants don’t, i.e. the area in the middle of the above graph, where blue is left, green is middle and red is on the right.

The study authors predicted that “A mode of phototrophy that is compatible with the plant’s photosynthesis would offer a significant ecological advantage to microbes inhabiting this environment.” And they indeed found that that is what happens. Brian Thomas’ problem, as I said, is that he doesn’t realise that the fact that this is advantageous means that natural selection will favour it, and instead thinks that this is evidence of Design and impossible for evolution:

Charles Darwin proposed that natural selection developed all living systems through a “struggle for life.” He imagined that competition between creatures built new biological structures to make them more fit to survive. But the specific biochemicals of these plants and bacteria enable them to cooperate without competing.

There are two points to be noted here before I finish. For one, intraspecific competition – competition between members of the same species – is generally more intense than interspecific competition. Secondly, this game theory type stuff is something that Darwin didn’t really know about at the time, but we do now.

To summarise, the study linked above (you can read the whole thing at that link) is quite interesting, but Brian Thomas’ article…isn’t. How surprising.


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