Wednesday, July 30, 2014

Built in maps

Bill Idsardi sent me this piece on bird navigation. It seems that Swainson thrushes have genetically built in maps that get them from Canada to Mexico and parts of south and central America. Moreover, it appears that these maps come in two flavors, some taking a coastal route and others taking a more medial one. As the author puts it, these routes can overlap and when they do (well let me quote here) "they have a chance to (ahem) mingle." Mingling has consequences and these consequences can apparently end up with mixed maps. As the researchers put it: "it is believed birds have genetic instructions on which direction they need to head and how long they need to fly," though, as conceded "it’s still a mystery how, exactly, a bird’s DNA tells it where to go."

This is interesting stuff (the area of study is called "vector navigation"). I bring it to your attention here for the obvious reason: whatever is genetically coded is very fancy: maps and routes. And despite the fact that the scientists have no idea how it is so coded does not stop them from concluding that it is so coded.  

This is quite different from the attitudes in the the study of humans, as you all know. Chomsky has pointed repeatedly to the methodological dualism that pops out whenever human mental capacities are studied. Were thrushes humans the usual critics would be all over themselves arguing that postulating such inborn mechanisms is methodologically ill advised (and not at all explanatory), that DNA could not possibly code for maps and routes, and that there must be some very subtle learning mechanism lying behind the attested capacities (almost certainly using some Bayesian  learning procedure while still in the egg!). In other words, standard scientific practice would have been suspended were thrushes humans.  You draw the relevant moral.


  1. Doesn't the paper in question claims that the maps (as opposed to the routes) are learned and not innate?

    " Results from orientation tests (e.g. radio-tracking of Swainson's thrushes, Cochran et al. 2004), suggest that this is largely an individual-based phenomenon, with migrants developing navigational maps from cues they learn on the first leg of migration to help complete subsequent trips. The development of these maps is beneficial, as they allow migrants to take more direct routes, revisit good stopover sites and avoid unfavourable areas"

    What is built in is not so fancy -- a vector (i.e. two parameters).

    1. Two comments: not surprisingly (to me) you run together two issues. The first is what the actual explanation is. Second what the acceptable range of explanations are. Your comment deals with the second. Here I don't have the expertise to comment, though the report in Discovery suggests that the authors do not interpret things as you report they do in the paper. As I noted in the first paragraph above in the main post, the authors believe that:

      "birds have genetic instructions on which direction they need to head and how long they need to fly," though, as conceded "it’s still a mystery how, exactly, a bird’s DNA tells it where to go."

      The birds they study that are from "mixed marriages" (and I inferred ONLY these) developed routes that are ones that neither parent takes, nor need they be even a mixture of what their parents do (the right down the middle is what neither parent does). They seem to think that this is individual but not because of learned cues (at least in the paper) buyt because of different "genetic instructions." At any rate, as I said, this is not anything I know much about so I will not get into an argument about what they may have shown.

      However, that was not the point of the post. The point was the insouciance regarding the possibility that much of this is innate. They do not place an upper bound on what they think is reasonable to put into the genes. They don't say, what a minute this can't be there! WHat they do is come up with an account of the behavioral patterns and then consider various admissible options, one of which is that there is a large genetic component to this migratory behavior. This is precisely what some in my field (yes you Alex) consider conceptual nonstarters from the get go. You KNOW that this is impossible and so inadmissible. How you know this is beyond me and the post was intended to buttress Chomsky's well know observation concerning methodological dualism in the study of human mental capacities. In other words, what is standard practice on other domain of biology is considered methodologically out of bounds when it comes to humans. Thanks for helping me make my case.

    2. Actually I am on board with Chomsky's critique of methodological dualism; I think he is almost entirely right on that.
      My point was narrowly about the fact that nobody is claiming that the maps are built-in, just the routes (direction + distance + a bit more maybe).

      If biologists were positing innate maps of the world (or the continent), in the absence of direct experimental confirmation (as there is with the migratory direction), and in conflict with standard views of evolution, that would indeed be "insouciant" but I don't see it.

  2. You are right about something else too -- we tend to project our own habits of mind onto research in other fields. So I see the problem of bird navigation, and I naturally think of the "minimal" solution. What is the smallest innate endowment that could explain this --- we should only posit the minimal amount of domain specific endowment because of what you call Darwin's problem. That seems (to me) like good science, whether it is in linguistics or passerine migration. I don't know quite what the alternative strategy would be in this case; but this seems like a good MP-ish stance.