After last Fridays post on a curiously orchestrated media event for a crappy paper (DUNT TAKE TEH PILL OR U CHOSE BAD BOIFREND!), I decided to bully some of my immuno professors for more information. I mean Ive got MHC experts just down the hall, surely they would know more about this topic!
ERV: “What the hell?? Did you read the news today??”
ERV: “Did you see that crappy paper about humans ‘sniffing’ MHC molecules and women on the pill???”
ERV: *explains crappy paper*
Professor: Its kind of a well known mating trick with mice. Youre trying to get your mice to breed, they wont, so you put a different mouses poop underneath the cages, and suddenly the mice want to mate. Probably has something to do with mice ‘smelling’ a different MHC peptide.”
Professor: “But humans dont have a vomeronasal organ.”
One way your body internalizes signals from the environment is through G-protein coupled receptors (GPCR). When receptors facing the environment interact with ligands in the environment, a chemical signal is turned into an ‘electrical’ signal your brain can interpret as a red rose or strawberry ice cream. These G-protein coupled receptors are like chemical sensors.
So just like there are specialized cells in your eyes and nose using specialized GPCRs to detect light or smells, mice (and snakes, and some other animals) have a structure in their noses, the vomeronasal organ (VNO), to detect a different kind of ‘smell’. But the VNO is not just an extension of the nose (think of it as if you had a second pair of eyes that only saw in the UV spectrum). The GPCRs in the VNO do not recognize the same chemicals/molecules as the main olfactory system, and its not connected to your brain the same way as your nose. ‘Normal’ smells go to the olfactory lobe to be sorted into ‘WHOO! Thats popcorn!’ or ‘BLECH! Thats a pig feed-lot!’. Vomeronasal smells end up at the amygdala and hypothalamus.
So its not too surprising that mice and snakes use vomeronasal smells for mating and aggression and stuff the amygdala and hypothalamus control. So why cant humans use our ‘second smell’ for mating too?
Well, thats where we hit that bump in the road.
Humans dont have a vomeronasal organ.
Well, I mean we ‘have’ one like we ‘have’ tails. Its vestigial. It kinda develops when we are embryos, and then it goes away. Sometimes doctors can find it in patients, sometimes they cant (… on the same patient at a later time). But just because we cant see it doesnt mean its not just hiding or shrunk, and still fully functional. Luckily, we have GeneBank now. And we have evolution! A great trick to see if humans still have a functional VNO is to hunt for functional versions of the genes that code for the vemeronasal receptors! If the genes dont code for functional receptors, then there is no friggen way they are relaying information to our brains about our boyfriends MHC genotype (just like a color blind person aint gonna see green).
People have performed that little GeneBank hunt. Turns out about the time primates developed three-color vision and started relying on more visual cues for mating, selective pressure on the vomeronasal receptor genes started to go lax. Thus mice, who use their second smell every day, have >200 genes that code for vomeronasal organ receptors… and humans only have 4 or 5 putative genes, and >200 pseudogenes chock full of nonsense mutations, premature stops, insertions… theyre a mess.
Evilution is waving ‘bye-bye’ to our second-smell past.
So why are studies like ‘TEH PILL MAKE YOU SMELLZ MHC RONG!’ still going on? I have no idea. There must be some evidence that humans can communicate with different chemical signals (ie women living together get on the same menstrual cycle), and some labs appear to be trying to deal with the fact humans dont have VMOs… But the authors of ‘MHC-correlated odour preferences in humans and the use of oral contraceptives’ didnt even try to address the controversy around their field. Not even a reference to ‘Some people think…’.
But they sure had time to orchestrate a massive PR push for their pathetic data.
So like I said before, stupid crappy ‘science reporting’ and stupid crappy research. Ugh.