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Two Views of Biology: Structuralism vs. Functionalism

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Editor's note: In his new book Evolution: Still a Theory in Crisis, Michael Denton not only updates the argument from his groundbreaking Evolution: A Theory in Crisis (1985) but also presents a powerful new critique of Darwinian evolution. This article is one in a series in which Dr. Denton summarizes some of the most important points of the new book. For the full story,get your copy of Evolution: Still a Theory in Crisis. For a limited time, you'll enjoy a 30 percent discount at CreateSpace by using the discount code QBDHMYJH.

Regarding the fundamental nature of organic form, biologists have for two centuries adhered to two opposing conceptions. One is referred to as structuralism (or formalism), and the other as functionalism. I am going to explore each of these in turn.

ETSC square.jpegAccording to the structuralist paradigm, a significant fraction of the order of life and of every organism is the result of basic internal constraints or causal factors arising out of the fundamental physical properties of biological systems and biomatter. In other words, these constraints do not arise as adaptations to satisfy particular functional ends. One of the simplest examples of this kind of order, "structural order," is the cell membrane, which organizes itself into a thin layer covering the surface of the cell due entirely to the hydrophobic character of its lipid components -- i.e., due to physical law -- irrespective of any functional end it may serve.

These internal constraints, or "laws of biological form" as they were referred to in the 19th century, were believed by many biologists before Darwin to limit the way organisms are built to a few basic designs or Types, just as the laws of chemical form or crystal form limit chemicals and crystals to finite sets of lawful forms. This view implies that many of life's basic forms arise in the same way as do other natural forms -- ultimately from the self-organization of matter -- and are genuine universals.

Of course, all structuralists accepted that organisms exhibit adaptations to serve external environmental conditions. But these were considered to be "adaptive masks," grafted as it were onto underlying ground plans or "primal patterns." Thus the great diversity of vertebrate limbs -- fins for swimming, hands for grasping, wings for flying -- are all modifications of the same underlying plan or pattern, which serves no particular environmental necessity.

According to the opposing paradigm, often referred to as functionalism, the main fundamental organizing principle of biology is adaptation to serve various functional ends. On this view, the main type-defining homologs (pentadactyl limb, etc.) are not the result of physical law. Instead, functionalists see homologs as a result of adaptations built by cumulative selection during the course of evolution to meet particular environmental constraints. Adaptations built in this way are contingent in the sense that they are undetermined by natural law. According to the functionalist view, organisms are, in essence, like machines, contingent assemblages of functional parts arranged to serve particular adaptive ends.

This is, of course, the currently prevailing and mainstream view. All Darwinists, and hence the great majority of evolutionary biologists, are functionalist by definition, as all evolution according to classical Darwinism comes about from cumulative selection to meet functional ends.

It is hard to imagine two scientific frameworks as diametrically opposed as structuralism and functionalism. Where structuralism proposes an internalist model of causation, functionalism proposes an externalist causal model. It is extraordinary to think that leading biologists have seen exactly the same empirical facts as pointing in such very different directions.

The English-speaking world adhered to some version of functionalism for so long that it is inconceivable to most English-speaking biologists that living things might contain a significant degree of order that arises from basic internal physical constraints and could not be the direct result of any sort of adaptive process. And there is no doubt that the structuralist claim -- that the biological realm is undergirded by "crystal-like" ground plans or primal patterns specified in the laws of nature, which serve no specific external adaptive purpose and never have (although the adaptive masks built upon them certainly do) -- is very alien to English-speaking biology.

But that is precisely what I think the evidence in nature indicates. In Evolution: Still a Theory in Crisis, I cite various examples of non-adaptive structures including some of the basic ground plans such as the pentadactyl limb and the insect body plan. If I am correct, and these examples are fundamentally non-adaptive forms, they provide an existential challenge to Darwinian evolution.

Deep patterns in nature that are non-adaptive are completely out of the reach of Darwin's mechanism of natural selection, and necessitates positing new causal mechanisms beyond just-so stories and the contingencies of history. I suggest that it is time to reconsider the pre Darwinian model of life and the radical structuralist claim that life is an integral part of nature.

Image credit: © Silver / Dollar Photo Club.