The biogenetic law and the Gastraea theory: From Ernst Haeckel's discoveries to contemporary views

Abstract

More than 150 years ago, in 1866, Ernst Haeckel published a book in two volumes called Generelle Morphologie der Organismen (General Morphology of Organisms) in the first volume of which he formulated his biogenetic law, famously stating that ontogeny recapitulates phylogeny. Here, we describe Haeckel's original idea as first formulated in the Generelle Morphologie der Organismen and later further developed in other publications until the present situation in which molecular data are used to test the “hourglass model,” which can be seen as a modern version of the biogenetic law. We also tell the story about his discovery, while traveling in Norway, of an unknown organism, Magosphaera planula, that was important in that it helped to precipitate his ideas into what was to become the Gastraea theory. We also follow further development and reformulations of the Gastraea theory by other scientists, notably the Russian school. Elias Metchnikoff developed the Phagocytella hypothesis for the origin of metazoans based on studies of a colonial flagellate. Alexey Zakhvatin focused on deducing the ancestral life cycle and the cell types of the last common ancestor of all metazoans, and Kirill V. Mikhailov recently pursued this line of research further.

Beyond recapitulation: Past, present, and future

“…Recapitulation theory has inspired us to develop future research directions. Levit et al (2021) provide an interesting review of the history of Haeckel's contributions. With a special focus on the Gastraea theory (Haeckel, 1872) and recapitulation theory (Haeckel, 1866), they summarize how his original ideas have developed up until now.…”

Theories, laws, and models in evo‐devo

“…in Haeckel, 1873 , pp. 254–255; Levit et al, 2021 ). De Robertis and Sasai have commented: “Although simplistic, the Gastrea theory historically was very useful because it proposed that all multicellular animals were monophyletic” (De Robertis & Sasai, 1996 , p. 40).…”

“…This theory holds that development is a re‐run (recapitulation) of evolutionary history (Haeckel, 1866a , p. 7; de Beer, 1951 ; Gould, 1977 ; Kuratani et al, 2020 ; Levit et al, 2021 ; Olsson et al, 2017 ; Rádl, 1909 ; Richardson & Keuck, 2002 ; Russell, 1916 ). Meckel and Serres were early proponents of recapitulation (Meckel, 1811 , p. 3; M. Serres, 1827 , p. 82–85; E. R. A. Serres, 1860 , p. 401; reviewed by Gould, 1977 ; Jahn, 2002 ).…”

Oogenesis and embryogenesis in a cryptogenic species of calcareous sponge (Calcaronea, Heteropiidae) in the southwestern Atlantic

“…The Gastraea theory proposes that all metazoans derive from a hypothetical organism for which there is no paleontological evidence but that can be seen in the gastrulation stage in several living animals. Because he observed a "gastrula" stage in some calcareous sponges, he proposed that all animals, from sponges to mammals, had a common ancestor similar to this stage of animal development (Levit et al, 2022). Studies on reproduction and development helped to resolve doubts about Porifera belonging to the Metazoa lineage (Duboscq & Tuzet, 1937).…”