Haeckel believed that the development of an embryo revealed the adult stages of the organism’s ancestors. Haeckel represented this idea with drawings of vertebrate embryos at similar developmental stages. This is Haeckel’s embryo grid, the most common of all illustrations in biology textbooks. Yet, Haeckel’s embryo grids are much more complex than any textbook explanation. I examined 240 high school biology textbooks, from 1907 to 2010, for embryo grids. I coded and categorized the grids according to accompanying discussion of (a) embryonic similarities (b) recapitulation, (c) common ancestors, and (d) evolution.

Biology textbooks are everybody's business. In accepting the view that texts are created with specific social goals in mind, I examined 127 twentieth-century high school biology textbooks for representations of animal development. Paragraphs and visual representations were coded and placed in one of four scientific literacy categories, including descriptive, investigative, nature of science, and HETS, or human embryos, technology, and society. I then interpreted how embryos and fetuses have been socially constructed for students. I also examined the use of Haeckel's embryo drawings to support recapitulation and evolutionary theory. Textbooks revealed that publications of Haeckel's drawings were influenced by evolutionists and anti-evolutionists in the 1930s, 1960s, and the 1990s. Haeckel's embryos continue to persist in textbooks because they 'safely' illustrate similarities between embryos and are rarely discussed in enough detail to understand the role of comparative embryology in the support of evolution.