Ernst Haeckel formulated the known Fundamental Biogenetic Law, in which he describes the parallelism between embryonic development and the phylogenetic history, claiming that embryonic development is a rapid recapitulation of the evolution, or “ontogeny recapitulates phylogeny”. Most conservative people viewed Haeckel’s propositions as a challenge to the more religious views about the origin of man. Haeckel made comparisons between early embryos from different species; his famous drawings, that appeared in his works, especially in Natürliche Schöpfungsgeschichte, were famous at the time, and they were criticized by other scientists. Some people at the time claimed that the only evidences for this proposition were the drawings made by Haeckel, but we have to consider that experimental biology was at a sort of “very early stage of development”. Hence, Haeckel’s work was abandoned from the main stream of science, especially between the World Wars, when chemistry and physics gained much more attention. However, Haeckel’s work likely inspired many future scientists, including his students. One of them was Hans Spemann, who later made one of the most important experiments in biology. Even, when the findings of Spemann and Mangold can be considered as opposed to Haeckel’s biogenetic law (because now the embryological development is driven by hidden forces with molecular nature, and since all organisms are different, these forces should differ in nature), the work of Spemann led in time to the discovery and (partial) understanding of the Wnt pathway, which is maybe one of the most conserved signaling pathways in nature and one of the most important driving forces in embryological development, validating Haeckel’s work: indeed, embryological development involves the expression and function of conserved genes through evolution. This realization brought Haeckel’s work one more time into the public attention, and once again, critics to his work appeared, with high press coverage at the time.
Image attributed to Ernst Haeckel, published in his work Natürliche Schöpfungsgeschichte, and illustrates the similarities between embryos of different species (man, dog and turtle). His rivals argued that embryos compared in Haeckel’s drawings usually had abnormalities and that they corresponded to different developmental stages. Image source: Wikipedia Commons.
Today, two papers published in Nature (vol. 468, Number 7325) “recapitulate” this classic debate: Domazet-Lošo and Tautz show in Zebrafish that the transcriptome expressed during the phylotypic stage (the stage in which species from a phylum resemble each other) is older compared with the transcriptome expressed in adult stages. They conclude that “our study provides strong molecular support for a correlate between phylogeny and ontogeny”, which agrees with the propositions of Haeckel and previous researchers (like K. von Baer). In the same issue, Kalinka and co-workers took a similar approach with six Drosophila species, observing also maximal conservation of gene expression at the phylotypic stage. Haeckel was discredited by many scientists, even in these days. He has been accused to be convinced to fraud, showing that embryos in drawings are stylized, altering embryos, and heterochrony is not considered in the drawings itself. With the available tools nowadays, we know that embryological development is variable between species. I believe that this is not the point. Haeckel’s work helped to popularize an important idea in biology, and we can discuss at which extent conserved genes and signaling pathways are integrated in the early (or late) development, validating the general concept about the relationship between evolution and development.
It should be an outstanding improvement in scientific journals, to include historical profiles and short reviews (no more than one page) about these relevant figures in biology (and science in general).