ORIGINAL PAPER Alexei Sewertzoff and Adolf Naef: revising Haeckel’s biogenetic law Georgy S. Levit • Uwe Hossfeld • Lennart Olsson Received: 30 August 2014 / Accepted: 9 September 2014 Ó Springer International Publishing AG 2014 Abstract Ernst Haeckel formulated his biogenetic law, famously stating that ontogeny recapitulates phylogeny, in 1872. The Russian evolutionist Alexei Sew- ertzoff, and the Swiss-born zoologist Adolf Naef were among those who revised Haeckel’s law, thus changing the course of evolutionary theory and of develop- mental biology. Although Sewertzoff and Naef approached the problem in a similar way and formulated similar hypotheses at a purely descriptive level, their theoretical viewpoints were crucially different. While Sewertzoff laid the foundations for a Darwinian evolutionary morphology and is regarded as a forerunner of the modern synthesis, Naef was one of the most important figures in ‘‘idealistic morphology’’, which is usually seen as a type of anti-Darwinism. Both Naef and Sewertzoff aimed to revise Haeckel’s biogenetic law and came to comparable conclusions at the empirical level. This paper is an attempt to explain how their fundamentally dif- ferent theoretical backgrounds influenced their views on the relationship between ontogeny and phylogeny. Keywords Biogenetic law Á Ernst Haeckel Á Alexei Sewertzoff Á Adolf Naef Á Idealistic morphology Á Evolutionary morphology G. S. Levit Á U. Hossfeld Arbeitsgruppe Biologiedidaktik, Biologisch-Pharmazeutische Fakulta ¨t, Friedrich-Schiller- Universita ¨t Jena, Am Steiger 3, Bienenhaus, 07743 Jena, Germany G. S. Levit (&) Á U. Hossfeld ITMO University, Lomonosov Str. 9, 191002 St. Petersburg, Russia e-mail: georgelevit@gmx.net L. Olsson Institut fu ¨r Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universita ¨t Jena, Erbertstr. 1, 07743 Jena, Germany 123 HPLS (2015) 36(3):357–370 DOI 10.1007/s40656-014-0043-9