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Chapter 11 Recapitulation I myself am convinced that the theory of evolution, especially the extent to which it’s been applied, will be one of the great jokes in the history books of the future. Posterity will marvel that so very flimsy and dubious an hypothesis could be accepted with the incredible credulity that it has. —Malcolm Muggeridge, British journalist and author In 1874, a german comparative embryologist and Darwin enthusiast, Ernst Haeckel, began publishing his drawings of vertebrate embryos in various stages of development to explain common ancestry and to support Darwin’s theory of evolution. Haeckel drew the first phylogenies and coined the term “tree of life” (see chapter 13). His skillful and detailed drawings clearly showed that the early-stage embryos of many species of vertebrates are nearly if not wholly identical. With his drawings and accompanying descriptions , Haeckel promoted the idea that “ontogeny recapitulates phylogeny,” also called the biogenic law. The biogenic law states that the path of an organism during its embryological development (ontogeny) is a summary of its evolutionary history (phylogeny). For example, a human embryo has structures that resemble gill slits, just like a fish.The human embryo then loses these structures and grows a tail and four limbs, resembling a reptile.The tail disappears, and the embryo begins resembling a primate. Haeckel tirelessly promoted his biogenic law, and many biologists in the nineteenth and into the twentieth centuries embraced it as a simple explanation of evolution. How convenient that all we had to do was look at embryological development to understand an organism’s evolutionary history! While Haeckel had many supporters, he was not without his early critics. Almost immediately, many of Haeckel’s fellow embryologists noticed that he had taken artistic liberties in his drawings to support his ideas, yet few rejected the biogenic law outright. One of the first written criticisms of the biogenic law appeared in an 1894 article by zoologist Adam Sedgwick in the Quarterly Journal of Microscopic Science. Sedgwick argued that the biogenic law conflicted with a principle known as von Baer’s law, after Karl Ernst von Baer, one of the 99 CH011.qxd 3/26/09 5:30 AM Page 99 founders of embryology. Baer had noted, contrary to Haeckel, that the embryos of higher animal forms resembled the embryos, not the adults, of earlier forms.Thus, for example, a human embryo may pass through a stage in which it resembles a fish embryo, but not an adult fish. Sedgwick noted, “Embryos of different members of the same group are more alike than the adults, and the resemblances are greater the younger the embryos examined.” He continued that when the actual embryos were examined, “a blind man could distinguish between them.” As the twentieth century unfolded and the fields of empirical embryology and genetics emerged, it became clear that in his drawings Haeckel had emphasized similarities between the embryos of various vertebrate classes and neglected the differences. It is not clear whether he purposely altered his drawings to better fit his ideas. In any case, the drawings fascinated lay people and scientists outside the fields of embryology and evolution. Biology textbook authors looking for detailed and authoritative images to illustrate their chapter pages happily included the drawings. Due to the cost-effective practice of recycling images and their accompanying explanations, as well as the paucity or even lack of evolutionary biologists on the editorial staffs of textbook companies, the drawings remained in many textbooks until the 1970s. During this time, many teachers who had little or no background in evolution taught their students that the drawings were evidence of evolution, and the students were encouraged to understand and memorize the catchy phrase, “ontogeny recapitulates phylogeny.” Finally, in 1977, in his book Ontogeny and Phylogeny, Stephen Jay Gould carefully dissected Haeckel’s drawings and disproved the general ideas behind the biogenic law. Later, in one of his last essays in Natural History magazine (March 2000), Gould explained that while Ernst Haeckel was regarded among his contemporaries as a master naturalist, he often “took systematic license in ‘improving’ his specimens to make them more symmetrical or more beautiful .” Most likely as a result of Gould’s careful critique, Haeckel’s drawings are no longer found in today’s biology textbooks. Haeckel was not wholly wrong.As we will see later, phylogeny is indeed to some extent recapitulated in embryological development. What Haeckel got wrong, however, was his belief in the recapitulation of the adult forms. Rather, embryological...

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