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The so-called Biogenetic law: "Ontogeny recapitulates Phylogeny", asserts that an animal passes through the stages of its evolutionary history during development.
Paul Nelson replies:
Haeckel's practices were highly questionable,
even by the standards of the time. The distinguished historian
of embryology Jane Oppenheimer (1987, p. 134) notes, for instance:
It was a failing of Haeckel as a would-be scientist that his
hand as an artist altered what he saw with what should have
been the eye of a more accurate beholder. He was more than
once, often justifiably, accused of scientific falsification,
by Wilhelm His and many others. For only two examples, in
_Anthropogenie_ he drew the developing brain of a fish as
curved, because that of reptiles, birds, and mammals is bent.
But the vesicles of a fish brain always form in a straight
line. He drew the embryonic membranes of man as including
a small sac-like allantois, an embryonic organ characteristic
of and larger in reptiles, birds, and some nonhuman mammals.
The human embryo has no sac-like allantois at all. Only its
narrow solid stalk remains to conduct the umbilical blood
vessels between embryo and placenta. Examples could be
significantly multiplied.
Even more dubious was Haeckel's use of the same printing blocks to
illustrate embryonic stages in different species. As the Polish
physician and historian of science Ludwik Fleck (1979, p. 36)
observes,
When Haeckel, the romantic, high-spirited champion of truth,
wanted to demonstrate his ideas about descent, he did not
shrink from occasionally using the same blocks for the
illustration of different objects such as animal and
human embryos which should look alike according to his
theory. His History of Natural Creation abounds with
biased illustrations appropriate for his theory.
The Swiss embryologist Gunter Rager has reproduced some of these
illustrations in his 1986 article, "Human embryology and the law of
biogenesis" (Rager 1986). He writes:
On page 248 of the Naturliche Schopfungsgeschichte (1868)
Haeckel published 3 figures which were supposed to show the
embryos of a dog, a chick and a turtle, respectively. These
3 figures are completely identical. Even the asymmetry of
the 10th pair of somites and the number and length of lines
in...each of the figures are the same. (1986, p. 451)
Rager gives other examples from Haeckel's publications of the
same practice, calling the illustrations "faked material" and
"cheating tricks" (1986, pgs. 449 and 452). Whatever label one
wants to attach to Haeckel's practices, there is no reasonable
defense for using exactly the same diagram to illustrate three
different species.
Some have suggested that, Haeckel's law (or
von Baer's law) is very much alive and well, and that in a basic fashion,
ontogeny really does recapitulate phylogeny.
But Von Baer's laws differ profoundly from Haeckel's.
Indeed, von Baer formulated his generalizations precisely in opposition
to the sort of recapitulation Haeckel favored. In any case, neither
von Baer's laws, nor Haeckel's, are reliable generalizations today
about the patterns of metazoan ontogeny. Looking simply within the
vertebrates, for instance, the earliest stages of development are
strikingly different (e.g., between an amphibian, a chick, and a mammal).
For further discussion, see Raff (1996) or the latest edition of Scott
Gilbert's developmental biology text, and the literature cited therein.
References
Fleck, L. 1979. Genesis and Development of a Scientific Fact.
Chicago: University of Chicago Press.
Oppenheimer, J. 1987. Haeckel's variations on Darwin. In Biological
Metaphor and Cladistic Classification, eds. H.M. Hoenigswald
and L.F. Weiner. Philadelphia: University of Penn. Press.
Raff, R. 1996. The Shape of Life. Chicago: University of Chicago Press.
Rager, G. 1986. Human embryology and the law of biogenesis. Rivista
di Biologia - Biology Forum 79:449-465.
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