Gene expression patterns in chordate embryonic development suggest partial applicability of Haeckel’s postulates

The relationship between embryonic development and evolution historically investigated based on embryo morphology, could now be reassessed using mRNA expression endophenotype. Here, we investigated the applicability of von Baer’s and Haeckel’s arguments at mRNA expression level by comparing the developmental changes among nine evolutionarily distinct species: from oyster to mouse. In agreement with models based on von Baer’s postulates, up to 36% of mRNA expression indicated nearly linear conservation of species’ developmental programs. By contrast, 5-15% of developmental expression profiles, enriched in neural genes, displayed an alignment pattern compatible with the terminal edition paradigm proposed by Haeckel. Thus, the development-evolution relationship based on mRNA expression agrees with early concepts based on embryo morphology and demonstrates that the corresponding patterns coexist in chordate development.