The embryo drawings are still widely printed in reference books and student texts, and have therefore been widely accepted as teaching devices (Gould, 2000). They are also used in technical scientific publications (Duboule, 1994 ; Butler and Juurlink, 1987). Their modern use is to illustrate one or more of the same three points that Haeckel intended, namely : embryonic resemblance as evidence of evolution ; phenotypic divergence ; and recapitu- lation. The eight embryos from NatuW rliche SchoW pfungs- geschichte (Haeckel, 1874c) are redrawn in the modern text Biology (Arms and Camp, 1995), and were used to illustrate embryonic development in The Study of Animal Life (Thomson, 1917).
The most widely reproduced of Haeckel’s embryo drawings are the set in the first edition of Anthropogenie (Haeckel, 1874 a). In several text books, the drawings are used as scientific illustrations to show the reader what embryos look like (Wilson, 1886 ; Lull, 1927 ; Cole, 1933). They have been widely used in numerous standard works (e.g. Alberts et al., 1994; Collins, 1995 ; Gilbert, 1997) and in countless student texts (e.g. Kardong, 1995; Gould, Keeton & Gould, 1996; Gerhart & Kirschner, 1997; Mu$ ller, 1997). Embryo plates from later Anthropogenie editions are copied by some authors (e.g. Platt and Reid, 1967; Leakey, 1986). These texts faithfully reproduce scientific errors in Haeckel’s original (e.g. his depiction of the forelimb bud of the chick embryo, in the middle row of the plate, as being a caudal member of the pharyngeal arch series).
Some texts appear to have copied their drawings second-hand, rather than directly from Haeckel. The version in Darwin and After Darwin (Romanes, 1892) is the commonest secondary source (Fig. 6). Some books (e.g. Phillips, 1975; Minkoff, 1983).
Haeckel presented the embryo drawings as data in support of his hypotheses. Therefore, scientists disagreeing with Haeckel’s views have often chal- lenged the accuracy of the drawings (Richardson et al., 1997), and their interpretation. Other criticisms of the drawings, which will not be discussed here, are religious or political in motivation (e.g. Assmuth & Hull, 1915).
Wilhelm His was ideologically opposed to Haeckel’s views (Gerber, 1944 ; Richardson & Keuck, 2001) and used an empirical, morphometric approach to challenge the embryonic resemblances depicted in Haeckel’s drawings (see Section IV. 4b) below). Unfortunately, however, most scientists discussing embryonic similarity have done little more than make subjective judgements about overall appearances, and this approach to comparative embryology is essentially phenetic. For example, Yapp (1955 : p. 673) claims that : ‘ ... a 545 day chick and a 13-day rabbit embryo are almost indis- tinguishable ’. Dubious phenetic statements of this type reflect the lack of a rigorous approach to comparative embryology.
Scientific objections to Haeckel’s drawings (Table 2) include charges of : (i) doctoring (the alteration of images during copying); (ii) fabrication (the in- vention of features not observed in nature) ; and (iii) selectivity (the use of a misleading phylogenetic sample). Various authors have made these charges, as reviewed by Gursch (1981), who concentrates on non-scientific aspects of the controversy.
