Platonic Ideal Forms Versus Evolutionary Developmental Biology
In a recent thread at Uncommon Descent,
Salvador Cordova wrote:
"[The existence of] platonic forms would strongly suggest that [evolutionary] transitional [form]s don’t exist. And if there are only lawful morphological forms, transitional forms, even in principle, couldn’t exist. Transitional forms and Platonic Forms don’t fit well together in any theory. It appears the two are mutually exculsive.
In engineering we have many platonic forms. As engineers we are taught to recognize and implement certain canned architectures. A lot of systems biology is mapping biological forms to the forms engineers recognize.
[The] quest for “correct designs” ... makes sense in a world of ideal forms, platonic forms. We instinctively have platonic forms in our mind. We have a sense that a defect is a defect, that an error is an error.
In the Darwinian world, it’s all about selective advantage. A blind cave fish is “selectively advantaged”. Defect is only a relative term. However in the eyes of plato, a blind cave fish is less than the ideal, it is a broken form. In such case, natural seleciton helped to infuse the defect in the population and thus introduce a defect that is not consistent with the ideal pattern.
The notion of platonic forms does not seem to be compatible with Darwinian evolution. [Emphasis added]
The idea of Platonic ideal forms in biology is an old one. The now mostly defunct tradition of orthogenesis is essentially a version of Platonic ideal forms applied to biology (and an argument can also be made that Lamarck’s progressive theory of evolution by means of the inheritance of acquired characteristics is as well). However, and contrary to what some might expect, applying the concepts of orthogenesis to "intelligent design theory" ("ID") is problematic, because in its early 20th century form, orthogenesis was considered to be progressive, but not goal oriented (i.e. teleological).
In addition to the early orthogenesists, two other names stand out in this tradition: D’Arcy Thompson and Stephen Jay Gould. Both were primarily concerned with the origin and evolution of form, and both developed theories of evolution based on this. Even J.B.S. Haldane (one of the founders of the “modern evolutionary synthesis”) wrote in this tradition in his essay "On Being the Right Size". Haldane’s musings on the relationship between size and constraints on form have become known as “Haldane’s Principle”, and have recently been applied to urban planning.
The newly emerging science of evolutionary developmental biology (”evo-devo”) has some similarities to orthogenesis, especially insofar as both are attempts to explain why the evolution of overall form (i.e. phenotype) appears to be constrained to certain types of forms, rather than all possible forms. The orthogenesists asserted that there are certain forms that are much more likely than others. These forms are similar in some ways to Platonic forms, in that there is no necessarily materialistic explanation for the predominance of certain forms, at least according to the theory of orthogenesis.
Evo-devo explains the similarities within “formal types” with reference to shared developmental programs, especially among eukaryotes. This shared developmental programming is based on the hierarchical gene regulation systems, most of which are based on homeotic gene regulatory mechanisms. Similar developmental constrains appear to exist among plants and fungi, but not so much among prokaryotes and multicellular protists. So, looking for things that resemble Platonic ideal forms in biology will probably involve identifying and categorizing the various developmental “channels” which are produced by these homeotic gene regulatory systems.
None of this, of course, says how the various hierarchical gene regulation systems originally evolved. This is another of those “deep time” problems, such as the origin of life and the origin of the genetic code. As I have commented repeatedly in the past, I believe that questions about such origins are almost certainly unanswerable using current empirical methods.
I also personally believe that the question of the origin of Platonic ideal forms (if such things exist and are empirically distinguishable from the various “channels” produced by the action of homeotic gene regulatory mechanisms) is both an open question and one that is almost certainly not answerable using empirical methods.
For more on the question of Platonic forms in biology, see this and this.
For a critique of my analysis of Platonic ideal forms in biology, see this.
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As always, comments, criticisms, and suggestions are warmly welcomed!
--Allen
Labels: D'Arcy Thompson, evo-devo, evolutionary developmental biology, homeotic gene, hox gene, ideal form, idealism, Platonic idealism, Stephen J. Gould
posted by Allen MacNeill @ 4/08/2009 10:59:00 AM
3 comments
3 Comments:
Platonic ideals don't exist. (That was easy.) Platonic ideals are merely mental constructs our brains create in order to categorize and make sense of our world.
I mostly agree, with the following caveats:
1)Something like Platonic ideals do exist. As Tiny Frog points out, they exist in our minds. Another name for them is "concepts", which are generalizations about consistent patterns that we perceive in the world around us (and, in some cases, in our minds).
For example, consider sugar maple trees. These most definitely exist, and there is enough consistency in their structure and function (and also their underlying genetic information) that systematists have classified them as a distinct species, Acer saccharum. Furthermore, sugar maple trees would continue to exist and have the characteristics that they have regardless of whether humans had classified them or recognized them as being similar.
However, the United States of America also exists, but it exists entirely within the minds of those people who believe in its existence. The difference between sugar maples and the United States is not a difference in their "existence" per se, but rather where and in what form they exist.
2) In the case of sugar maples, there is something about the characteristics of individual sugar maples that impresses itself upon us in such a way as to recognize them as being classifiable as a "concept". That is, something about sugar maples causes the regularities in their characteristics that causes us to form the concept "sugar maples" in our minds. Ergo, there is a "real" regularity in the sugar maples themselves, of which our concept of "sugar maples" is a more or less accurate representation.
However, I do not agree at all with the Platonic tradition that says that "ideal forms" exist independently of the individual objects out of the similarities of which concepts are formed in our minds. Again, those similarities would be there regardless of whether there were anyone who could recognize or formalize them.
Where do the regularities in living things come from? for evolutionary biologists, the answer is from a combination of causes, including the genomes of the organisms (inherited genetically from their ancestors) and from the similarities in their ecological circumstances, which produces convergence in characteristics as the result of similar selective pressures and developmental influences.
Evo-devo does not intend to show that there are some "platonic forms", has might be understood from this post.
The fact that after all, there are much fewer body plans that previously thought, makes more sense of Evolution!.
It is much easier to explain how a few gene networks evolved to become more and more complex, but with constrains on body plans, rather than how completely different genes and different plans emerged.
The evo-devo framework shows how all animals are connected in a deep sense, and not hoe intelligent design or platonic forms exist.
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