Charles Murtaugh reports, and links to other reports, that the similarity score between human and chimpanzee DNA is down from 98.5% to 95% or so.

Robert Musil muses that maybe the chimp’s “junk” DNA overlaps the human’s “working” DNA or vice versa; Paul Orwin sets him straight, convincingly. With all due respect to the real scientists in this discussion, like Murtaugh and Orwin, I think everyone is missing the point.

People care about the similarity of human/ape DNA because they are in the grip of what I will call, since there is no term in logic that I know of to describe it, the mapping fallacy. The mapping fallacy is the belief that similar inputs to a function generate similar outputs. That depends on the function. For f(x) = x + 1, sure. For f(x) = x³, a qualified yes, as long as you hold x down to a reasonable size. For certain complex functions, useful in cryptography, not at all: they generate a completely random-looking output for any change in the input, no matter how small.

To return to biology: our input, x, is the genetic sequence; our output, f(x), is the resulting life-form. We know x produces f(x), but we have no idea how. Maybe two radically different genetic sequences produce the same life-forms. Maybe two scarcely distinguishable sequences produce completely different ones. The point is, we don’t know, because we don’t know what sort of function, or mapping, we’re dealing with here. And until we do know, no one should much care whether human and gorilla DNA are 95% similar or 98.5% or 99.44% similar.

Mapping fallacy examples:

• Stephen Wise, the animal rights guy du jour, arguing that chimpanzees should have rights because we have 98.3% (apparently a compromise figure) of our DNA in common.
• Jared Diamond, a distinguished biologist who ought to know better, arguing that the concept of race is absurd because there are larger genetic differences within than among races. (I agree with Diamond about race but that doesn’t make his argument any more respectable.)
• The BBC story I linked above, arguing that the percentage dispute is important because “…the relatively small difference between human and chimp genomes would offer insights into the gene differences that might render humans more vulnerable to disease.”

(Update: The Man Without Qualities comments further, complaning mildly that Orkin did not exactly “set him straight,” conceding, on the contrary, that the study under consideration does not distinguish between “useful” and “junk” DNA. Fair enough. Now if he would only link to my post, instead of my email address, we could all go home happy.)

Good site. Go browse if you haven’t yet. I broke my maidenhead there for Mass Post Day by recycling my old Salinger piece and got accused of plagiarizing Ian Hamilton’s biography, a book I haven’t read and don’t intend to read, for my trouble. Sheesh.

(Update: Apparently the guy who accused me of plagiarism spoofed someone’s identity to do it. See the comments. Not ironic exactly, just weird.)

Eugene Volokh quotes an excellent letter on prescriptivism vs. descriptivism in language, or why it’s OK to say “NU-kyu-ler.” H.W. Fowler, author of Modern English Usage, the greatest of all “prescriptive” guides, had this to say (under the heading “pedantry and purism”):

Pedantry may be defined, for the purpose of this book, as the saying of things in language so learned or so demonstratively accurate as to imply a slur upon the generality, who are not capable or desirous of such displays. The term, then, is obviously a relative one; my pedantry is your scholarship, his reasonable accuracy, her irreducible minimum of education, and someone else’s ignorance….

Purism is like pedantry, except that it does not necessarily imply a parade of superior learning. Now and then a person may be heard to ‘confess’, in the pride that apes humility, to being ‘a bit of a purist’; but purist and purism are for the most part missile words, which we all of us fling at anyone who insults us by finding not good enough for him some manner of speech that is good enough for us…. Pure English, however, even apart from the great number of elements (vocabulary, grammar, idiom, pronunciation, and so forth) that go to make it up, is so relative a term that almost every man is potentially a purist and a sloven at once to persons looking at him from a lower and a higher position in the scale than his own.

And Fowler was supposed to be a prescriptive grammarian. My own experience with language pedants is that the less they know, the likelier they are to insist on some particular niggling point or other.

(Modern English Usage appears not to be online. As a dictionary, albeit a highly eccentric one, it would be an ideal candidate. Fowler’s other book, The King’s English, is, but it isn’t nearly as good.)

VodkaPundit writes about using “SteveCase” as an obscene epithet to circumvent the AOL chat police, and that works just fine for the standard four-letter epithets. But if you hit your thumb with a hammer, it’s just not satisfying enough to say “SteveCase.” You need something richer, more mellifluous — something like “Boutros Boutros-Ghali,” (brief pause between the two Boutroses). Or maybe “Buttafuoco,” which enjoyed a brief epithetic vogue in the early 90s, when Joey was making the scene at Moomba. It did. Really.