For two hundred years, scientists have noticed that the appearance of embryos in related species converge in their appearance mid-way in development, diverging thereafter. But is this 'phylotypic stage' real, and how is it connected with the genetic basis of development? Here, a method linking the genes transcribed at various stages of development (the transcriptome) with the evolutionary history of those genes is used. Genes transcribed in the phylotypic stage are, in evolutionary terms, the oldest and most conserved. This suggests that the phylotypic stage does represent the body plans of related species at their most unadorned, selection having sculpted the earlier and later stages of embryonic form to suit the particulars of each creature.