As far as the evolution of the principal animal
groups is concerned, is there any correlation between
the burst of gene duplications of signalling components
and the phylogenetic diversification of these taxa?
Some recent results indicate that extensive duplications
of genes that encode signalling molecules might have
occurred at least twice, once before the divergence of
the PARAZOANS and the EUMETAZOANS (~1,070 Myr ago)
and again around the divergence of the CYCLOSTOMES and
the GNASTHOSTOMES (~500 Myr ago)41 (FIG. 2). According
to this analysis, the Cambrian explosion, the period
~520 Myr ago during which many phyla are thought to
have originated was, however, not accompanied by
gene duplication.