The Origins of Insects

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Science  07 Jun 2002:
Vol. 296, Issue 5574, pp. 1767
DOI: 10.1126/science.296.5574.1767a

In phylogenetic studies, the molecular clock hypothesis has become the basis for figuring the dates at which evolutionary lineages of organisms diverged. The number of nucleotide substitutions along the length of a branch of a phylogenetic tree is a surrogate parameter for the age of the branch. Because of variation in substitution rates, however, reliable molecular clocks are sometimes hard to identify.

Using GenBank sequence data, Gaunt and Miles have now been able to define a robust molecular clock for the insects—the most diverse of animal groups—that identifies the deepest nodes in the phylogenetic tree and is in accord with the fossil record. According to this clock, the earliest insects cleaved from their nearest relatives, the fairy shrimps, about 430 million years ago, close to the emergence of the first land plants. — AMS

Mol. Biol. Evol.19, 748 (2002).

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