Papal Approved

Visiting the Chicago Field Museum a day before my 25th (yup) college reunion at the U of C, Heather and I noticed a great big sign, posted over the entrance of the new Evolving Planet exhibit. It said:

LIFE EVOLVES

This unapologetic, non-mealy mouthed acclamation pleased me. Heather, the screaming, blue-painted Celt troublemaker that she is, tasted blood and liked it even more. Particularly in the context of her belief that the Carnegie Museum of Natural History here in Pittsburgh soft-pedaled the issue in their new dinosaur exhibit in order to avoid riling the local religious right wing. [1]

For me, though, the sign took me right down memory lane — specifically, to a 1950s-era Catholic-school edition of Modern Biology, a middle-school biology textbook that I’d inherited from my aunts, still teenagers when I arrived. [2]

I recall a disclaimer in the beginning, which said something to the effect that the Vatican neither accepted nor denied the Theory of Evolution, but only commented on the fact that only human beings had souls and the scientific theory had no bearing on the status of Adam and Eve as the first humans.

I’m sure a lot of folks will read that as sleight-of-hand to evade a scientific steamroller without actually admitting to any changes in doctrine. But this son of Abruzzo and Sicilia (not to mention New Jersey) — steeped, perhaps, in too many centuries of Vatican inevitability — read it differently: It was the Church’s way, the Galileo debacle still smarting in retrospect, of sanctioning a simple acknowledgment of reality with, to put it mildly, considerably more grace than it did in 1633. [3] The Church, let’s face it, is a vast ship that turns only very slowly.

(Hey, along those lines, keep an eye on Cicada magazine — Barnes & Noble usually either carries it or can order it for you. My historical short story “And Yet It Moves” will appear in their Jan./Feb. 2009 issue.)

All by way of saying, I’ve got a deal of cultural baggage, and thus I feel reassurance every time the over-arching theme of natural selection — which really hit me over the head, throughout my graduate school studies in biochemistry — gets a boost, substantive or moral. When it also speaks to an important aspect of my hobby, olfactory science, I’m delighted.

Submitted for your approval: an evolutionary study by Wendy Grus and Jianzhi Zhang of the University of Michigan that confirms some guesses scientists had been making about the difference between the olfactory system and the accessory olfactory system.

Here’s the rub: Most vertebrates (though maybe not us and the great apes) possess two smellers. Within the nasal cavity lies the olfactory epithelium. Embedded in the vomer bone in the nose sits another olfactory organ: The vomeronasal, or Jacobson’s, organ.

Best theory to date said that the olfactory system responds to smells as we understand them, but the VNO gets its signals from pheromones — airborne hormones that play a role in mating and other social interactions. This idea suggested a couple of amazing things off the bat:
* Because pheromones exert their action on a hormonal level, animals (and maybe humans, since VNO-like receptors appear in the human olfactory epithelium) probably respond to them without being aware of it.
* If so, airborne chemical signals may affect human behavior without us knowing it — think on the times you’ve instinctively liked (or not) another person on sight, or the fact that people tend to marry folks with crucial genetic differences linked to the VNO.

Grus and Zhang looked at another prediction made by the odors v. pheromones hypothesis: Namely, that olfactory receptors need to recognize any smell that comes along, while VNO receptors and their signals need to respond only to tightly controlled, species-specific chemical signals that developed on an evolutionary timescale.

This is profound: People have described the VNO receptors, without hyperbole, as a major engine of the evolutionary process: In order to remain within a species (i.e., stay in its mating pool), you have to remain responsive to its airborne mating signals, and only those signals. Once you lose that, you’re well on the road to becoming a new species. On the other hand, if two species respond to each others’ signals (and live close enough to each other to mate), they won’t remain two species for long (hence the concerns about red wolves mating with coyotes).

The Michigan Moleculeers found — after a buttload of lab work, one reason why yours truly is today a scientific dilettante — the evolutionary fingerprint of this distinction, etched in the vertebrate genes. Looking at olfactory receptor genes and VNO receptor genes in the mouse, rat, dog, opossum, platypus, chicken, and frog, they discovered that the olfactory genes don’t vary much between species, but the VNO genes do, in a way that parallels their evolutionary relationships.

You’d expect this, based on the proposed functions of the two organs: The olfactory receptors need to respond to the same huge spectrum of possible smells, and so they should vary as much within a species as between species — but nature has to rework the VNO receptors every time a new species splits off. The investigators followed up with a functional analysis of these genetic changes, nailing down that the VNO-associated changes actually alter the parts of the receptors that recognize odorants.

So that’s it — it’s a pretty neat result, in that it uses the hard facts of the molecules to tie together behavioral and evolutionary theory in a way that strengthens both. And if you’re Catholic, don’t worry: My read is that this result carries Papal approval.

[1] To be fair, I’m not sure I agree with her; certainly, there’s a lot to like about the new Carnegie exhibit, and it’s vastly superior to what it was before the modernization project (in case you didn't know, Andy Carnegie made sure his pet museum was at the forefront of the 19th-century dinosaur craze, and so they have a superlative collection of fossils). Having said that, I think I like the exhibits at Chicago or the American Museum of Natural History in New York better — at least until Pittsburgh opens up its Cretaceous exhibit, the absence of which, frankly, irked me at the reopening.
[2] I haven’t linked to the new textbook of that name, since I’ve no idea whether it bears any relation to my aunts’ book.
[3] Beyond embarrassing, as if that needed to be said. We only officially cleared him in 1992. The Vatican used to have a fantastic historical section on Galileo on its website, but I can’t find it at the moment; they redesigned the site since I last visited.