Beyond Haeckel's Law: Walter Garstang and the Evolutionary Biology that Might Have Been.

At the beginning of the twentieth century Haeckel's biogenetic law was widely questioned. On the one hand, there were those who wanted to dismiss it altogether: ontogeny and phylogeny did not have any systematic or interesting relation. On the other hand, there were those who sought to revise it. They argued that while Haeckel's recapitulationism might have been erroneous, this should not deter the research over the relation between evolution and development. The British embryologist Walter Garstang was one of the main figures on the "revisionists" side. In this paper, I first situate Garstang's contribution to embryology and evolution within the extraordinarily creative period of the first three decades of the twentieth century. Then, I review some of Garstang's specific ideas in detail, especially his most well-known 1922 paper "The Theory of Recapitulation." Finally, I look at how the demise of the biogenetic law in light of Garstang's views-as well as from the perspective of contemporary developmental evolution-should be understood. My main concern is not about the dismissal of Haeckel's law or the sidelining of embryology in the twentieth-century evolutionary biology. I am rather interested in exploring why Garstang's revised version of biogenetic law-which was entirely consistent with the neo-Darwinian perspective underpinning the Modern synthesis-did not spur a major new agenda in evolutionary biology after the 1930s.