page_title: Embryo drawing
section_title: Ernst Haeckel (1834-1919)
hierarchical_section_title: Embryo drawing / Famous embryo illustrators / Ernst Haeckel (1834-1919)
caption_attribution_description: Romanes' 1892 copy of Ernst Haeckel's allegedly fraudulent embryo drawings. Romanes version is often attributed incorrectly to Haeckel.
context_page_description: Embryo drawing is the illustration of embryos in their developmental sequence. In plants and animals, an embryo develops from a zygote, the single cell that results when an egg and sperm fuse during fertilization. In animals, the zygote divides repeatedly to form a ball of cells, which then forms a set of tissue layers that migrate and fold to form an early embryo. Images of embryos provide a means of comparing embryos of different ages, and species. To this day, embryo drawings are made in undergraduate developmental biology lessons.
  Comparing different embryonic stages of different animals is a tool that can be used to infer relationships between species, and thus biological evolution. This has been a source of quite some controversy, both now and in the past. Ernst Haeckel pioneered in this field. By comparing different embryonic stages of different vertebrate species, he formulated the recapitulation theory. This theory states that an animal's embryonic development follows exactly the same sequence as the sequence of its evolutionary ancestors.
context_section_description: Haeckel's illustrations show vertebrate embryos at different stages of development, which exhibit embryonic resemblance as support for evolution, recapitulation as evidence of the Biogenetic Law, and phenotypic divergence as evidence of von Baer's laws. The series of twenty-four embryos from the early editions of Haeckel's Anthropogenie remain the most famous. The different species are arranged in columns, and the different stages in rows. Similarities can be seen along the first two rows; the appearance of specialized characters in each species can be seen in the columns and a diagonal interpretation leads one to Haeckel's idea of recapitulation.
  Haeckel's embryo drawings are primarily intended to express his theory of embryonic development, the Biogenetic Law, which in turn assumes (but is not crucial to) the evolutionary concept of common descent. His postulation of embryonic development coincides with his understanding of evolution as a developmental process.  In and around 1800, embryology fused with comparative anatomy as the primary foundation of morphology. Ernst Haeckel, along with Karl von Baer and Wilhelm His, are primarily influential in forming the preliminary foundations of ‘phylogenetic embryology’ based on principles of evolution.  Haeckel's ‘Biogenetic Law’ portrays the parallel relationship between an embryo's development and phylogenetic history.  The term, ‘recapitulation,’ has come to embody Haeckel's Biogenetic Law, for embryonic development is a recapitulation of evolution.  Haeckel proposes that all classes of vertebrates pass through an evolutionarily conserved “phylotypic” stage of development, a period of reduced phenotypic diversity among higher embryos.  Only in later development do particular differences appear.  Haeckel portrays a concrete demonstration of his Biogenetic Law through his Gastrea theory, in which he argues that the early cup-shaped gastrula stage of development is a universal feature of multi-celled animals.  An ancestral form existed, known as the gastrea, which was a common ancestor to the corresponding gastrula.
  Haeckel argues that certain features in embryonic development are conserved and palingenetic, while others are caenogenetic. Caenogenesis represents “the blurring of ancestral resemblances in development,” which are said to be the result of certain adaptations to embryonic life due to environmental changes.  In his drawings, Haeckel cites the notochord, pharyngeal arches and clefts, pronephros and neural tube as palingenetic features.  However, the yolk sac, extra-embryonic membranes, egg membranes and endocardial tube are considered caenogenetic features.  The addition of terminal adult stages and the telescoping, or driving back, of such stages to descendant's embryonic stages are likewise representative of Haeckelian embryonic development.  In addressing his embryo drawings to a general audience, Haeckel does not cite any sources, which gives his opponents the freedom to make assumptions regarding the originality of his work.
caption: Romanes' 1892 copy of Ernst Haeckel's allegedly fraudulent embryo drawings (this version of the figure is often attributed incorrectly to Haeckel).[6]
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