Pre-Darwinian Homology

Thursday, January 22nd, 2009 | Theory

In a recent post Malte C. Ebach and David M. Williams criticize a paper by Anastasia Thanukos for bringing up the concept of common ancestry into the definition of homology. Their criticism seems a little harsh to me since, as they noted, the paper is aimed at Science teachers and it is therefore written on a “text-book” tone. This issue aside, however, I find their complain somewhat out of touch.

Their main argument is an historical one, namely that the concept of homology predates the general acceptance of evolution, and hence its definition should remain non-evolutionary. Not doing so will be “whiggish history”. They seems not to realize, however, that the language of science, its concepts and definitions, behave like scientific hypothesis themselves, changing and adjusting as more knowledge about the world accumulates. Yes, surely Belon did not think in evolutionary terms and Owen was a closeted transmutationist, but they did realize that there was something behind those patterns that called for an explanation, they just didn’t know what it was (or were not ready to accept). Their pre-darwinian concepts and definition of homology reflected the standards of their times, something that prepared Natural History for the big change in the way of viewing things that was about to come.

But today, objecting to the notion that the human five-fingered hand and the five-toed foot of a lizard, as homologous features, were both inherited from our common ancestor is equivalent to objecting at the definition of water as H2O. Water, and most of its properties, were know before the atomic theory of elements, but it is through this theory that we are now able to explain and predict the behavior of this compound. Today, we gain nothing by insisting on a non-atomic definition of water.

Like Ebach and Williams, I am fond of pre-darwinian concepts (as the title of this blog should reveal), and thus welcome that historians and philosophers of science are shifting focus away from Darwin an into the interesting nineteen century science that has been eclipsed by The Origin of Species. I also share the view that the discussion on just how much we need to assume about the evolutionary process in order to reconstruct evolutionary patterns is an interesting one. On a general level, I do think that questioning our epistemological limits is a healthy exercise. Nevertheless, I also share John S. Wilkins recent remark that one shouldn’t make of the pattern everything that there is.

Ebach and Williams close their post stating that “[t]here is a misconception in science that everything needs to be explained.” Well, in science everything does need to be explained. That the explanation into why we have a given paraphyletic group has to do with a taxonomist’s misjudgment or preference for non-natural groups rather than due to the existence of some evolutionary processes is another matter.

References
Anastasia Thanukos (2008). Bringing Homologies Into Focus. Evolution: Education and Outreach, 1 (4), 498-504 DOI: 10.1007/s12052-008-0080-5