Ontogenetic Depth 2.0: The Prequel
Okay. First admit the obvious.
Ontogenetic Depth (OD) 1.0 was -- well, it would be beyond charitable to say utterly inadequate. I realized this not long after reading PZ Myers' first wave of criticisms. As I'll explain, however, my realization stemmed not from Myers' specific points (most of which were either minor quibbles, or missed the mark completely), but rather from trying to apply OD 1.0 myself to the well-studied models systems of developmental biology. The OD 1.0 "metric" was no metric -- measuring stick -- at all. Thus, PZ's general judgment in 2004, if not his specific criticisms, was dead accurate: "This is a poorly expressed and unusable idea."
To my happy astonishment, however, trying to fix OD 1.0 took me far deeper into problems with current evolutionary theories than I could have imagined. OD 1.0 claimed "ontogenetic depth is a measure of the distance (in terms of cell division and differentiation) between a single-celled state and an adult animal (metazoan) capable of reproduction." Yet if one tries to apply this hopelessly crude metric to compare animal ontogenies, and assess the evolutionary distance between them, one will discover that the features most important for understanding the origin and macroevolution of animal form -- my original preoccupation -- are entirely neglected. To capture those features requires a more precise measuring stick (or set of different measures); but just how much more precise, I could not have realized in 2003, when "ontogenetic depth" first popped into my head as a fancy term to attach to the cell lineages of C. elegans and a couple of other model systems.
But the deeper journey to try to fix OD 1.0 wasn't simply a matter of finding better measuring sticks. As the now-notorious 1999 Chengjiang conference illustrated, no evolutionary theorist had even a glimmer of insight into the origin of animal form. C.H. Waddington's 1966 aphorism, that the "the whole real guts of evolution -- which is, how do you come to have horses and tigers, and things -- is outside [the Modern Synthesis]," turned out to be even more the case after the rapid rise to prominence of evo-devo in the 1980s. Most biologists (not to mention scientists in other fields) think that evolutionary theory tells us how the animals came to be: horses, tigers, chordates generally speaking; but echinoderms, too, and arthropods, and molluscs, and cnidarians -- you know: the origin of the animals. That's what Darwin was all about.
Nobody knows. And when one tries seriously to solve the problem, it gets much worse. A problem that explodes in difficulty the deeper one looks is a problem that ought to make one question background assumptions. In this OD 2.0 series, that's what I intend to do.
In his 2004 critique of OD 1.0, PZ Myers argued that the idea was intended to flesh out intelligent design. "Paul Nelson...has been peddling a peculiar idea he calls 'ontogenetic depth' as a scientific concept that emerges from Intelligent Design." But that wasn't my original intent. Like most ID theorists with a background in evolutionary theory, I'm as much -- probably more, in fact, given the embryonic state of ID theory -- a student of evolution. OD 1.0 was intended to give some handle of what is required to build an animal where none existed before.
That's not a problem for intelligent design. Designers make complicated things where they didn't exist before. PZ Myers "poofs" hundreds of sentences of English prose into existence every day. No magic required.
Rather, building animals de novo by known biological (evolutionary) processes is an evolutionary problem. Common descent by natural selection is the main theory on the table in 2010. It's the theory that, in this OD 2.0 series, I hope to show does not work.
In so doing, I'm not developing ID theory. That's a (very) different project. Rather, I'm working within the current evolutionary paradigm.
But I don't have to stay there if that paradigm crashes.
First up: What PZ Got Right and What He Didn't