A Failed Bet

Here is a nice explanation of some science history from: Duboule D and Wilkins AS (1998) The evolution of “bricolage.” Trends in Genetics 14: 54–59.

Although there was abundant evidence by the mid-1970s that many of the products of specialized cell differentiation, the hemoglobins, insulin, steroid hormones, and so on, were widely shared in metazoans, little was known about the regulatory machinery in any of the animal phyla.  It was clear, however, that to understand the evolution of different forms would require understanding the evolution of the molecular and cellular regulatory machinery.  Yet just how similar or how different the regulatory molecules and mechanisms might be between butterflies and bats was anyone’s guess.  Most biologists, however, would probably have bet that diversity and difference in the underlying molecular systems was the general rule.

The work of the past two decades and, in particular, that of the past eight years has demonstrated the reverse: the key regulatory molecules and mechanisms across the world of metazoan are remarkably constant.  Indeed, this wholesale conservation of molecular machinery has been one of the most striking findings of recent years.  The conserved molecules include virtually all the important classes of transcription regulator and all the forms of the various signal transduction systems, from those based on tyrosine kinase receptors to ion channels. Furthermore, not only can identifiable homologues of these genes be found, but it is also known that several of the conserved molecular systems play comparable general roles in pattern formation and organogenesis in animals that have overtly different adult morphologies and developmental systems. (emphasis added)

So once again, it should be clear that even though the Modern Synthesis had been completed by the 1970s and 80s, it failed to guide scientists about the something as crucial as understanding the evolution of different forms.  You may as well say it missed the target on the most important question in evolution.  Has this point begun to sink in yet?

Most biologists would have bet “that diversity and difference in the underlying molecular systems was the general rule.”  If they turned out to be correct, the hypothesis of front-loading would be extremely weak (and I doubt my book or this blog would exist today). If that bet was won, the machinery needed to generate the different forms would have come into existence along with the different forms, long after any putative design event.  As it turns out, this machinery not only is the same machinery among the different forms (much like the same hardware running different software), but thanks to what we have learned in the last 10 years since Duboule and Wilkins wrote those words above, we also know it pre-existed the different forms.  “The work of the past two decades and, in particular, that of the past eight years,” made front-loading a serious hypothesis.

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2 responses to “A Failed Bet

  1. I wonder what an actual fair survey of the literature would show about what biologists actually thought about this question over the years. This story is always told in the service of the “EvoDevo is the Big New Thing” storyline, and then copied by creationists and other people interested in their own revolutions. But the idea of anatomical homology for e.g. all animals goes way way back. E.g. “coelomate”, “bilaterian”, Geoffrey St. Hilaire, etc.

  2. Hi Nick,

    I don’t think Duboule, Wilkins, Newman and Bhat are simply telling a story to serve some storyline in the peer-reviewed literature. As Mike Levine explained:

    In the case of the discovery of common homeotic genes among all animals, there was a strong sense in the ’70s and the ’80s that embryonic development among different animals involved completely different molecules, completely unrelated. This was such a strongly held view.

    As for revolutions, none here. Your stereotypes are causing you to misperceive again.

    As for anatomical homology, sure that goes way, way back. But did conventional theory teach that the legs of mice and flies were homologous? Did conventional theory teach that the eyes of mice and flies were homologous? Nope. As Newman explains:

    It came as a big surprise to workers in the fields of evolutionary and developmental biology to learn a decade ago (Quiring et al. 1994) that the Drosophila eyeless (ey) gene, mutations of which cause loss or reduction in size of eyes, has extensive DNA sequence similarity to the mouse and human Pax-6 genes, which when mutated reduce the size of the mammalian eye. Before this unexpected finding, insect and vertebrate eyes were believed to be analogues—independently evolved structures playing similar or corresponding functions—not homologues— structures whose similarity is based on a common ancestral prototype (e.g., Salvini-Plawen and Mayr 1977).

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