Re: Behe on Kansas in Today's NYT

Moorad Alexanian (
Sat, 14 Aug 1999 11:13:11 -0400

I think this whole thing of what embryos look like is nonsense. Folks, we
are in the atomic age and what matters is the description at the molecular
level andnot what appears to the naked eye of humans.


-----Original Message-----
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Date: Friday, August 13, 1999 5:00 PM
Subject: Re: Behe on Kansas in Today's NYT

>Greetings to One and All:
>Once again Behe is leaving certain crucial facts out his essay.
>> For example, let's look at three claims of
>> evidence for Darwinian evolution
>> often cited by high school textbooks.
>> Third, the embryos
>> of fish, amphibians, birds and
>> mammals look virtually identical in an early
>> stage of development, becoming
>> different only at later stages.
>> The story of the embryos is an object lesson
>> in seeing what you want to see. Sketches of
>> vertebrate embryos were first made in
>> the late 19th century by Ernst Haeckel, an
>> admirer of Darwin. In the intervening years,
>> apparently nobody verified the accuracy of
>> Haeckel's drawings.
>This is untrue, because in fact a large number of professional scientists
>used their own microscopes to compare Haeckel's drawings with their own
>preparations. Only a very few challenged the accuracy of Haeckel's
>nearly everyone accepted that Haeckel was being accurate, based on the
>standards at the time. What most of them opposed was Haeckel's theory
>explaining this similarity. Haeckel proposed that because ontogeny
>progressed by recaptulating adult phylogeny, early embryos looked alike
>because they were in an early stage of ontological development, which
>represented an early stage of phylogenetic development. In other words,
>Haeckel was saying that embryos evolved their way from a single cell to a
>fully developed modern form. von Baer represented an early group of
>objectors. He stated that the phylogenetic structures that were being
>recapitulated were fetal structures, not adult structures, and that their
>recapitulation was coincidental to ontological development, not the cause
>that development. However, he and his colleagues had no viable theory of
>ontological development to replace Haeckel's. His (Wilhelm His)
>a later group of objectors. His rejected recapitulation altogether and
>claimed that ontological development was a physiological phenomenon caused
>changes in cell growth rates. Because His rejected recapitulation, he also
>challenged the accuracy of Haeckel's drawings. His' concept of ontological
>development eventually proved correct, but only after the rediscovery of
>Mendelian genetics provided the mechanism that his theory lacked. Until
>then, Haeckel's theory remained dominant. In point of fact, it was never
>refuted; it was simply abandoned as the growing science of genetics made it
>irrelevant. Even so, von Baer's recognition of the recapitulation of
>embryonic features was readopted and applied to Haeckel's famous statement
>that ontogeny recapitulates phylogeny. Only now, instead of being the
>driving force behind embryology, it is simply a consequence of embryonic
>development. For more details see _Ontogeny and Phylogeny_ by Stephen Jay
>> Prominent scientists
>> declared in textbooks that the theory of
>> evolution predicted, explained and was
>> supported by the striking similarity of
>> vertebrate embryos. And that is what
>> generations of American students have learned.
>> Recently, however, an international team of
>> scientists decided to check the drawings'
>> reliability. They found that Haeckel had, well,
>> taken liberties: the embryos are significantly
>> different from each other. In Nature, the head
>> of the research team observed that "it looks like
>> it's turning out to be one of the most famous
>> fakes in biology."
>What Behe doesn't state is that this team wasn't challenging the idea that
>embryonic development supports evolution; what they were challenging were
>specific hypotheses based on the concept of the common body plan, which in
>chordates is called the "pharyngula". This is stated in a letter they
>to _Science_ (280:5366, 983-986) after creationists started using their
>report to criticize evolution: "Hackel's drawings are used in many modern
>textbooks, but not always as primary evidence for evolution. In _Molecular
>Biology of the Cell_, the drawings are used mainly to support hypotheses
>about the stages of development acted on by natural selection. It is only
>this limited context that we have reservations about the implications of
>drawings." The only evidence they chose to examine were Haeckel's
>despite the fact that -- contrary to their claim -- they are no longer the
>most significant evidence in support of these hypotheses. The tone of the
>article is due largely to the lead author, Michael Richardson, who
>has an axe to grind against Haeckel (based on personal communications and
>subsequent comments in Nature).
>> What's more, the embryonic
>> stages shown in the drawings are actually not
>> the earliest ones. The earliest stages show
>> much greater variation.
>What Behe fails to mention is that this is old news to embryologists; Behe
>also fails to mention the actual relationship these various embryonic
>have with each other. Embryologist have known for a long time that the
>of the common body plan, known as the phylotypic stage, is preceeded by a
>fair number of earlier stages. This is necessary, however, because the
>elements of the body plan arise during these earlier stages. Embryologists
>have also known for some time that many aspects of development in these
>stages differ between classes and even between orders and families. There
>are two types of differences: differences in egg size, shape, shells and
>accessory food sources, which are provided by the mother and the germline
>cells before fertilization; and differences in the extra-embryonic tissues
>developed by the embryo itself. Yet despite all these differences, some
>aspects of development are conserved, and it is these that produce the
>elements of the common body plan, which for chordates is chiefly the
>notocord, the dorsal hollow nerve cord, the pharyngeal gill pouches and the
>post-anal tail. This body plan is possessed by all chordates, including
>ascidians, even though the the exact form of the pharyngula differs from
>class to class, and even between orders and families. These differences
>created by the different developmental stages leading up to the chordate
>phylotypic stage. Then of course, further development after the pharyngula
>has formed causes the embryos to diverge further as they develop the adult
>form. However, some aspects of post-phylotypic development are also
>conserved, thus constraining this divergence. See _Cells, Embryos, and
>Evolution_ by John Gerhart and Marc Kirschner for more details.
>In any event, the point is this. Behe implies that development between
>chordate classes, orders and families are now seen to be virtually
>but this is untrue. All known chordates have different developmental
>pathways for oogenesis, primary and secondary axis specification,
>endo-mesoderm induction, organizer inductions, gastrulation and
>but they all end up at the same intermediate developmental stage with the
>same basic body plan. This is the stage that Haeckel drew, and most modern
>embryologists agree that all chordates go through this stage. Even the
>authors of the report Behe mentioned agree with this: "On a fundamental
>level, Haeckel was correct: All vertebrates develop a similar body plan
>(consisting of a notochord, body segments, pharyngeal pouches, and so
> This shared developmental program reflects shared evolutionary history.It
>also fits with overwhelming recent evidence that development in different
>animals is controlled by common genetic mechanisms." They later state:
>suggest that Haeckel was right to show increasing difference between
>as they develop. He was also right to show strong similarities between his
>earliest embryos of humans and other eutherian mammals (for example the cat
>and the bat)." Their only major complaint was that by drawing the embryos
>having virtually no differences at this stage, Haeckel implies that there
>virtually no evolutionary change in early embryonic stages of development.
>> But I would also want them to learn to make
>> distinctions and ask tough questions. Questions
>> we might discuss include these:
>> If supposedly identical embryos were touted
>> as strong evidence for evolution, does the recent
>> demonstration of variation in embryos now count
>> as evidence against evolution?
>According to the authors of that report, the answer is no. Again from the
>letter to _Science_: "Our work has been used in a nationally televised
>debate to attack evolutionary theory, and to suggest that evolution cannot
>explain embryology. We strongly disagree with this viewpoint. Data from
>embryology are fully consistent with Darwinian evolution." "Unfortunately,
>Haeckel was overzealous. When we compared his drawings with real embryos,
>found that he showed many details incorrectly. He did not show significant
>differences between species, even though his theories allowed for embryonic
>variation." "This does not negate Darwinian evolution. On the contrary,
>mixtures of similarities and differences among vertebrate embryos reflects
>evolutionary change in developmental mechanisms inhereted from a common
>ancestor." "Thus, certain 'phylotypic' embryonic stages, which Haeckel
>showed as identical, may in fact be significant targets for natural
>selection." "Haeckel's inaccuracies damaged his credibility, but they do
>invalidate the mass of published evidence for Darwinian evolution.
>Ironically, had Haeckel drawn the embryos accurately, his first two valid
>points in favor of evolution would have been better demonstrated."
>In other words, embryonic variation (which has been known for sme time and
>was not just recently demonstrated as Behe claims) actually strengthens
>evolution rather than weakens it.
>> If some
>> scientists relied for a century on an old, mistaken
>> piece of data because they thought it supported
>> the accepted theory, is it possible they might
>> even now give short shrift to legitimate contrary
>> data or interpretations?
>As long as analyses like the one Behe mentioned are published, I doubt that
>will become a problem.
>What I find more troubling is Behe's insistence upon mischaracterizing
>research in order to make his case. This is the third instance I have
>discovered of this trend in as many months. This is a trait of political
>activists, not scientists.
>Kevin L. O'Brien