Coragyps

This may be a rather long post on a rather obscure subject, so let me offer a little justification up front. Many, or most, in the young-earth creationist camp deny that humans are related to other animals, and also deny that there is such a thing as a "vestigial organ." However, the vomeronasal organ is a little whoopus in the human nose that offers some serious difficulty for any YEC explanation I can anticipate. I will readily admit that there are two reasons that I dug all the following up: 1) I like the sound of the word "vomeronasal," and 2) I'm a member in good standing of the II "Needs a Life Club."

First things first: the vomeronasal organ (VNO) is associated with, but not identical to, the organs of smell. It is particularly well developed in snakes, many other reptiles, and many mammals, particularly rodents and ungulates. It is normally a pair of lobes located in the roof of the mouth/floor of the nose area, and typically with connections to both mouth and nose. It has nerve connections to the accessory olfactory bulb (AOB) of the brain. The organ seems to be used for at least two purposes: tracking prey in snakes, and tracking the opposite sex in mammals. A snake flicks its tongue in and out, transferring odorant molecules to the VNO. A bull raises his head, curls back his upper lip, and inhales, checking out whether some little heifer is really in heat. These functions don't seem to be mutually exclusive, though. In many cases, at least in mammals, the "odorants" that the VNO responds to seem to be much less volatile that the things the normal olfactory system senses: mice and Guinea pigs (and dogs?) are always and forever sniffing on the rear end of their conspecifics, apparently because there must be liquid transfer of some of the steroid-like compounds that the VNO is particularly tuned to. They are "odorless" as far as the "regular" sense of smell is concerned, as not enough of them get airborne for the nose to pick up.

Now, on to primates. Here's a family tree:
| |----------Platyrrhini (New World monkeys)
| |----------Catarrhini (humans, other great apes, Old World monkeys)
|-------|
------| |----------Tarsii (tarsiers)
|
|-------------------Strepsirhini (lemurs, lorises...)

The "primitive condition" for the primates appears to be that of having a VNO: strepsirines, platyrrines, and tarsiers all have them, use them for sexual/social signalling, and have them wired into the AOB of their brain. But among us catarrhines, the situation gets murky. In macaques and baboons, the organ starts to form in the embryo, but never "makes" - as born, these species have only a slight thickening at the appropriate place in the septum of their noses. (Gorrilla and orang fetuses haven't been studied, but the adults have no VNO either.) In chimpanzees and humans, the fetus develops a pre-VNO similar to those of, say, a lemur. As the fetus develops, this structure migrates slightly upward (away from the mouth) and finally forms a very simple pair of tubes which may not always even open into the nostril. These tubes lack (or have only a very few) cells that appear to be sensory in nature. There are no obvious nerve connections leaving the human or chimp VNO. No brain structure like the AOB has been identified in adult humans or chimps, though one is present in human fetuses. The few glands that feed into the tubes are apparently just regular mucus glands, like those in the rest of the nose.

Work on genes associated with the VNO have found several in humans that are homologs of those in mice - but all so far investigated are psuedogenes: they're not functional. The issue of whether humans use the VNO for sexual or social signalling is not yet settled, though. Some studies seem to show physiological response to certain compounds, which could arise from the VNO. The normal olfactory circuits haven't been ruled out as the sensor here, though. ( There is no doubt that some sort of odorant response is used for such signalling in humans. One well known study showed that a compound in sweat is responsible for the well-documented synchronization of menstrual cycles in women who are dorm-mates. Another that might be documentable is my reaction to women wearing Tresor perfume.)

Finally, to the relevance of all this to this forum. I'll couch this in an argumentative way, as questions that I would like Ken Ham or Dr Dino to answer for me:
1) How do you explain the pattern of occurence/partial occurence/absence of the vomeronasal organ among the primates? Why should some monkeys have them, some lack them, and humans and chimps alone among the "ape kind" have something that looks just like a broken one?
1a) Why, for that matter, would humans, the pinnacle of creation, have a broken organ just like a dirty old chimpanzee's?
2) If the human VNO is NOT a "vestigial organ," do we use it for sniffing out suitable mates? That sure sounds awfully "animalistic," and not real refined, either. ( Must be part of the Curse.)
3) If the human VNO IS vestigial, does that make it the only "vestigial organ?" The common YEC claim is that there is no such thing.

I'll post some links/references in another post tomorrow - much of what I found will turn up in a Google search using "vomeronasal" with either "Meredith" or "Bhatnagar" as search terms. These two seem to be among the most prolific VNO researchers. And I must add: "If this has been a blessing to you, please consider a cash or beer contribution to ......

Duvenoy

Very interesting, Coragyps! Looking forward to the next installment.

In snakes and lizards, this is called, "Jacobson's organ" and it's pretty amazing. As noted, the forked tongue fits into grooves in the roof of the mouth. All scent particals are processed there. It's directional; the fork that has the most particals tells the animal the direction from which the scent comes. Komodo monitors can find carrion from a great distance.

In venomous serpents, mainly those such as pitvipers that envenomate and release, it get's even better. The venom changes the scent of the injured prey so that the snake can 'track' it among the scents of others of the prey's species.

Wonderful, is it not?

doov

Dr.GH

"The venom changes the scent of the injured prey so that the snake can 'track' it among the scents of others of the prey's species."

Cool, I did not know that part! Thanks. Do you have a citation for that?


Re: da shnoshozola

"Paranasal sinus anatomy of Aegyptopithecus: Implications for hominoid origins." by James Rossie et al, PNAS-USA vol. 99 no.12:8454-8456, might also be of interest here.

Duvenoy

Hi Doc,

Go here:

<a href="http://www.venomousreptiles.org/" target="_blank">http://www.venomousreptiles.org/</a>

And you may learn more about hot snakes and gilas than you ever wanted to know.

Even my last bite is written up there (under another nom de guerre).

doov

lpetrich

On a related subject, see <a href="http://www.gate.net/~rwms/primegendist.html" target="_blank">this primate genetic-distance table</a>.

I experimented with it using the phylogeny software package PHYLIP, since those numbers made my eyes glaze over after the first few rows. The runs agreed on the overall family tree, and even the details close to our species. However, different runs would place macaques at different places relative to baboonlike monkeys, sometimes amidst them, sometimes alongside them. Here's an ASCII diagram, with the presence or absence of a functional vomeronasal organ indicated by a + or - as appropriate:
[code]
/--------Rabbit (outgroup) +
\/-------Prosimians (lemur, loris, tarsier) +
\/------New World monkeys +
\/-----Old World monkeys -
\/----Gibbon -
\/---Orangutan -
\/--Gorilla -
\/-Chimps -
\-Human -
</pre>[/quote]

Notice the +'s above the NWM's and -'s below the OWM's

By the principle of parsimony, one tries to postulate as few changes as possible; here, the most parsimonious hypothesis is that the VNO was lost only once, when the catarrhine (OWM/ape/human) ancestor had split off from the platyrrhine (NWM) ancestor, but before its descendants went their separate ways.

However, if the VNO had been lost more than once, it is strange that it had been uniformly lost across a well-defined group.

[ June 18, 2002: Message edited by: lpetrich ]</p>

lpetrich

I note in passing that William Jennings Bryan's denunciations of evolution included a remark that he considered funny -- he objected to evolutionary biologists proposing that we are descended from Old World monkeys instead of New World ones, which he considered an additional put-down.

One of the last sane

It is believed that the flehmen response, or "lip curl" in bulls and stallions may be associated with the vomeronasal organ

Oolon Colluphid

Excellent, Coragyps! <img src="graemlins/notworthy.gif" border="0" alt="[Not Worthy]" /> May I add it to my list please?

Bear in mind that being used or not is irrelevant to ‘vestigiality’. Creationists love to find uses for such features, however tenuous. And so, they say, it has a function, it’s not vestigial.

But they miss the point. A vestige is simply a leftover; vestigial just means a greatly reduced (in function and/or morphology) version of something. This assumes evolution, and so ‘vestigial’ can be an unhelpful term in E/C discussions, unless we’re careful.

However, what we take to be ‘vestigial’ parts can also be seen from a design perspective -- ie the creationist one. Let it have a function, it doesn’t matter. What does matter is that, if the thing was designed, it has irrelevancies of design -- aspects of form not related to, or relevant for, its function.

You could say that eg the coccyx is vestigial because it is made from separate pieces of vertebra-shaped bones which were formerly a tail... thus begging the question.

Or you could say that having separate pieces of bone that fuse to a single one is a pointless -- and revealing -- piece of design: to do its job as a single bone, it does not need to be made from separate pieces, let alone vertebra-shaped ones. So evolution is the better explanation, and, if they want it designed by a creator, their creator is a poor designer.

He who lives by the intelligent design argument dies by the intelligent design argument.

I’m not sure how the VNO fits this scheme... will have to give it some thought...

Cheers, Oolon

Coragyps

Please do!

Some references:
E. B. Keverne has a review in Science: 22 Oct 1999, vol 286, pp 716-720
M. Meredith has an overview <a href="http://www.neuro.fsu.edu/research/vomer.htm" target="_blank">here.</a>
[URL= <a href="http://www.sru.edu/depts/pt/NewAnat2001.pdf" target="_blank">Paper]</a> by Smith and Bhatnagar.
<a href="http://www.neuro.fsu.edu/abstracts/HumanVNO.pdf" target="_blank">Review by Meredith.</a>

[ June 20, 2002: Message edited by: Coragyps ]</p>

Undercurrent

Of course it is. If we conceed we are related to African monkeys, sooner or later those evil scientists will try to tell us that we're related to Afrcan people.

Coragyps: Great post. Too bad any creationist that happens upon it won't get halfway through the secnd paragraph before their eyes gloss over. It's a shame that arguments fo evolution can't be effecively described in two sentences that rhyme with each other like creationst arguments can.

m.