Monday, January 4, 2016

The deep conservatism of biological systems; some lessons for linguists

Linguistic theory and biology have long had a mutually beneficial trade in ideas. Kai Jerne (here) explicitly cites the influence of Generative Grammar on the way he approached the immune system (here). The Principles and Parameters (P&P) theory and the Monod-Jacob theory of biological switches drank from the same stream of ideas and Chomsky has long noted the similarity of his Rationalist take on biology to that of ethologists like Tinbergen, Lorenz and von Frisch.

The most recent instance of the convergence/influence of views comes with the rise of Evo-Devo (ED) adjustments to the standard Darwinian story of natural selection. Here, I want to focus on one property of such accounts that I believe carry an important lesson for grammatical theory; the deep conservation of basic biological mechanisms. Let me explain with an illustration.

One of the big unexpected ED discoveries concerned the eye. The hero of this little tale is Walter Gehring (WG). Here’s a potted history of what WG discovered (based on this very accessible paper (here) by Gehring and Ikeo (G&I)). Prior to Gehring’s work the eye was the poster child for analogous evolution; the idea you can get the same “organ” via different evolutionary routes. Based on comparative and structural studies, the standard account was that “the photo receptor organs … originated independently in at least 40, but possibly up to 65 or more different phyletic lines” (371). The basis for this view? The “obvious” physical differences between the different kinds of eyes. G&I describes the state of play before Gehring’s work as follows:

Their section on ‘the multiple origin of eyes’ begins with the comment that ‘it requires little persuasion to become convinced that the lens eye of a vertebrate and the compound eye of an insect are independent evolutionary developments’. This point has been taught to biology students for over a hundred years. (371)

This turned out to be wrong. In other words, despite the evident surface differences among eyes in different species, nonetheless they all are basic variations of the same basic design. Or put another way, these different eyes all have a common ancestor, all stem from a common prototype, the differences being bells and whistles added to shared basic design. In an important sense then, there is only one eye.[1]

Btw, before saying a bit more about this, it is worth noting an interesting side comment that G&I make on Darwin’s views of natural selection, specifically concerning the origin of the eye prototype. Here’s the relevant wording:

Darwin was highly self-critical in his discussion of the eye prototype and admits that the origin of the prototype cannot be explained by natural selection, because selection can only drive the evolution of an eye once it is partly functional and capable of light detection. Therefore, selection cannot explain the origin of the eye prototype, which for Darwin represents the same problem as the origin of
life. Therefore, both the origin of life and the origin of the eye prototype must have been very rare events, and a polyphyletic origin in over 40 different phyla is not compatible with Darwin’s theory. (371)

In other words, according to Darwin, the emergence of prototypes cannot be accounted for in terms of Natural Selection, rather Natural Selection presupposes such rare events. No prototypes, no tinkering. Moreover, the emergence of prototypes must be very rare events. Sounds more than a bit like Chomsky’s proposals for the origins of recursion doesn’t it? So the next time you hear someone say Chomsky’s views are incompatible with evolution (i.e. that the sudden emergence of Merge makes no evolutionary sense), tell them to go and look up Darwin’s discussion of the emergence of the eye.

Ok, back to the main point.  What’s the new basic view of the evolution of the eye? There is a master control gene responsible for all eyes that is shared across all sighted creatures from Drosophila to mice to humans. In other words, there is really only one eye that are based on the many of the same basic building blocks. P&P indeed!

Any implications of this for linguistic theory? Not logical ones, but very suggestive ones.  Two in particular come to mind.

First, that “evident” surface differences in biology are not reliable signs of different mechanisms. This holds just as true (or should do so) in linguistics as in other parts of biology. I have discussed this recently (no doubt ad nauseum) here and here. But the point is an important one given the temptation to believe what is right before one’s eyes. This may sound like good common sense, but if science has taught us anything it is that things that look very different might nonetheless be exactly the same. In fact, what we consider the highlights of scientific insight basically consist in showing that two things that have entirely antagonistic properties are actually at bottom identical.[2]

Second, that biology finds it very hard to truly innovate. In other words, that there is basically only one way of doing anything. This suggests skepticism whenever a linguistics paper suggests that more than one way of doing anything. For example, there is a current view within syntax that there are two very different kinds of relative clauses formed using two very kinds of operations (matching vs movement). This view is buttressed by showing that these two constructions have different properties and the inference is made that such different properties require different kinds of operations to explain them. That is, of course, one way to explain surface differences. However, perhaps we should resist this inference until dragged kicking and screaming to the conclusion.[3] Why? Because multiplying mechanisms comes at the cost of explanation AND because it looks like biological systems don’t like doing anything two ways. So if you are a thoroughly modern GGer who understands the enterprise in cog/bio terms then you should be reluctant to ever multiply mechanisms. In short, as a general methodological rule of thumb, you should assume that there is only ever one road to Rome.

The proliferation of theoretical mechanisms is an easy way of covering apparently different properties. And, in fact, it is logically possible that variation signals divergent mechanisms. However, the successful sciences, in particular physics, has got to where it is by strongly resisting this mode of inference. It was supposed that this might be good for physics but not for biology where typically many mechanisms that can result in what look like the same effects. We now know that this is not quite so at the smallest cellular levels and ED is showing us that this is likely not even so at the macro level. Not only are living things more or less the same in micro, but it seems that our macro organs (e.g. eyes) are also built in more or less the same ways as well. I suggest that we adopt the same stance within linguistics. Our regulative ideal should be that FL/UG never does anything in two different ways.

[1] Just as there is fundamentally only one language, or more precisely one FL. Or put another way: impressive surface differences among languages do not imply different underlying etiologies.
[2] My good and great friend Elan Dresher once observed that there are really only two kinds of theoretical linguistic papers. The first shows that two things that appear radically different are more or less the same. The second shows that things that are more or less the same are in fact identical. Yup.
[3] For a provocative and interesting discussion resisting these temptations within current syntactic theory, see Dominique Sportiche’s paper Neglect (here). It is very much in the spirit of Gehring’s efforts regarding eyes.


  1. I'd like to offer a measured dissent. (At least I hope it's measured.) I think the work arguing that there are two ways to derive relative clauses is extremely insightful; it's linguistics at (or near) its best. If someone can then come along and find a way to unify things, that's all the better (though skimming the Sportiche paper you linked to, he relies on a notion of "crash" at the interfaces, so color me skeptical). But we wouldn't even know that there was anything to unify if not for that work.

    To put this another way, in order to be impressed with Gehring's work you have to first appreciate the nontrivial surface-diversity that is at play. If I told you that every species that took closeup photos of Pluto did it in the exact same way, I suspect you wouldn't be as impressed.

    So with all due respect to Elan Dresher's adage, I think papers saying "these two things that look like they're the same are really profoundly different" are very valuable (full disclosure: I've written one or two papers of this sort myself, so I'm obviously biased). First, it keeps the unifiers honest: after all, unifying is easy right up until you need to get the details right. Second, it tells us something about the range of things that our One True Mechanism is capable of generating, which I think brings us closer to – not further from – a proper understanding of that mechanism.

    1. Oddly, I completely agree. Methodological ideals are not dispositive and maybe the case of RCs is one where it fails. However, it is a good general assumption, I believe, and one motivated by these biological discoveries (*or made more plausible by them).

      SO why do I agree with your point? Because OF COURSE the right way of proceeding is via the HARD work of unification. It is always useful to look at where things LOOK like they differ for showing that they do not actually do so is an accomplishment. Showing that two things that look similar are indeed similar (or the same) is not something that one generally gets kudos for (rightly IMO). So, you are right that the advice does not imply that looking for differences is nugatory. Wghat it does endorse is the view that one should not be quickly satisfied that one has found two different mechanisms. One wants very high standards of proof for this conclusion. This is a standard minimalist trope: we want high burdens of proof from those that violate our methodological maxims. This is the theme of the 93 minimalist paper, and I believe that it still holds.

      As for your skepticism re interface crash; I was expecting it and you may be right, though it makes for a very nice conceptual story.