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Core muscle proteins are present in sponges that lack true muscles


And, via independent (convergent) evolution, we are told, humans, insects, and jellyfish have the same type of muscle cell.

From Patrick R. H. Steinmetz et al’s Letter to Nature, “Independent evolution of striated muscles in cnidarians and bilaterians” (Nature 487, 231–234 (12 July 2012) doi:10.1038/nature11180), we learn,

Muscles stretch back a long way

The ultrastructural similarity between striated skeletal muscles in higher bilaterian animals, such as humans and insects, and non-bilaterian animals, such as jellyfish, suggests a common evolutionary origin of this important contractile cell type. However, the precise evolution of striated muscles has not been confirmed. In this phylogenomic study, Ulrich Technau and colleagues show that core muscle proteins are present in unicellular organisms, such as sponges, that do not have true muscles. Their analysis supports a convergent-evolution model for striated muscles. According to this model, novel proteins were added to the ancient contractile apparatus during the independent evolution of the cnidarians and bilaterians, resulting in strikingly similar ultrastructures.

Should there be a new term for this type of evolution, of a faculty that could not obviously be of use to the life form that possesses it? But might be to others?


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