Orthologous nature of mammalian insulin genes.

Investigation of 17 insulin sequences from a bony fish, a bird, and 5 mammalian species showed that guinea pig and coypu insulin, that have a strongly divergent primary and quarternary structure, are not the result of gene duplication in an ancient vertebrate or invertebrate ancestor but they they diverged from the other mammals after divergence of the mammals from the other vertebrates. After this divergence both insulins underwent evolution at a highly increased rate.