Immunology Woo: MHC Mates, Part 3

My first tech job out of college, I worked with a lovely group of Chinese ladies. They gave me a Chinese nick-name meaning: dog nose.

Im working under the assumption that this wasnt an Anti-Semitic thing (lol!), but a comment on my really sensitive sense of smell. I would walk into the lab, smell gas, and be like "OMFG DID SOMEONE LEAVE THE GAS ON??" and they were like "Um, we had it on like 30 minutes ago..."

I hate cologne and perfumes. They literally make me ill (either sick to my stomach, if I can run away, or a migraine if I cant escape).

But I love, love, love the smell of a sweaty guy. Not like, sweaty guy socks, but a nice, fresh guy whose been outdoors and smells like sun + sweat... awesome *dreamy look*.

This probably has something to do with my particular genotype of OR7D4.

Contrary to what some labs (and basically all of pop-science media) wants you to believe, this probably has nothing to do with the MHC type of the sweaty guys I find so appealing:

Absence of Evidence for MHC-Dependent Mate Selection within HapMap Populations--
There is evidence in numerous species that genes involved in immunity influence mate choice. Factors like body odor may subconsciously favor partners with different immunity alleles, to avoid inbreeding and/or endow offspring with broad resistance to pathogens. A previous study, based on HapMap genotypes, reported that European-American mates were extremely dissimilar from each other in immunity alleles compared to non-mates. Upon re-examining the results and methods, and visually comparing mates and non-mates, we found that this effect was weak, strongly dependent on extreme pairs and on arbitrary choices in methodology, and not significant after correcting for the multiple hypotheses tested. More importantly, examination of new couples from the same population did not support this hypothesis. Rare instances of very high MHC similarity among non-mates suggest that mates may avoid extreme similarity, rather than favoring dissimilarity. However, too few samples are readily available to test this prospect rigorously. We conclude that HapMap samples do not conclusively support the hypothesis that MHC genotypes exert an influence on mate choice. The same previous study reported that Yorubans appear to prefer mates who are more genetically similar to themselves overall. Our analyses suggest that the effect is driven by a subset of the sample.

Quick recap-- Some people think that people are more attracted to people with different MHC alleles than they have. Mixing up these alleles is better for the future offspring. Mice have ways of 'smelling' this similarity/difference of other mice, and choose opposites. Humans dont have the organ we would need to 'smell' differences anymore. People keep publishing this stuff anyway.


So these folks looked at the data from other people who had published on this topic, saying that humans DO select for opposites (even though we have no VNO and there is no alternative biochemical pathway suggested). They looked at data from Mom-Dad-Baby trios to see who females and males actually picked as their mates, and the resulting MHC-type of their offspring.

Basically, a few outliers were skewing the data, and there is not much of an impact of MHC-type and humans hooking up:

We found that the previously reported MHC dissimilarity among Hap2 European-American mate pairs is apparent but not robustly supported by the underlying genotypic evidence. In addition, the effect essentially disappears in Hap3 for a similar number of independent couples from the same population, and is weak and insignificant for the combined Hap3 cohort.

So unless there is some big revolution in MHC-mates (figure out a plausible biochemical pathway, nice robust data), Im going to be leaving this field of research in the 'woo' file.

Hat tip to sweaty Scibling Blake ;)

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Called my(mandarin) adopted engineer uncle. He posits that "Dog's Nose" is a reference to one of a million Chinese proverbs and was a probably a compliment about being pointed in the right direction. (Ambitious/driven)

By Prometheus (not verified) on 10 May 2010 #permalink

Doing your part to encourage exercise, I see.. :P

time to get on the bike...

By complex field (not verified) on 10 May 2010 #permalink

While this seems to be strong evidence against the claims made about MHCs I don't think it is fair to describe this as woo. This is an example where a few papers suggested a link and further investigation has shown that they were wrong. That doesn't make it woo. That makes it an incorrect hypothesis. If people keep making these claims in the future that would then potentially become woo. Not only is calling this woo unfair to the scientists in question, but it gives way too much respectably to serious woo. Homeopathy is craptastic for example. The level of wrongness of most forms of woo is so much higher than anything here that calling this woo gives the serious crap a spill-over of seriousness.

@5: the research wasn't woo: the miles of pop-sci coverage insisting that science has shown that humans have pheromones was woo.

By Stephen Wells (not verified) on 10 May 2010 #permalink

Do you prefer the smell of a sweaty guy solo, or with a companion?

In a series of experiments designed help scientists understand the brain chemicals that guide mate selection, Pfaff and his colleagues exposed female mice to odors of either a male mouse alone or a male mouse with a female. The females consistently preferred the scent of males linked to other females.

But I love, love, love the smell of a sweaty guy.

Chacun à son goût.

::shaves:: (and ::doesn't work out::)

But I love, love, love the smell of a sweaty guy. Not like, sweaty guy socks, but a nice, fresh guy whose been outdoors and smells like sun + sweat... awesome *dreamy look*.

I run outside through the woods and stuff, but something tells me you wouldn't like how, for lack of a better word to describe it, "spicy" I smell when I get back.

By Kemanorel (not verified) on 11 May 2010 #permalink

The bit about; mice have the organ for sensing this, but humans don't 'any more', is intriguing. Is it that we still have genes that 'could' make the organ, but they're not expressed. Might be a good experiment if we could make them express again and see what that leads to.

Could we engineer people that are attracted to my favourite tunes and not lady gaga?

@ERV: I'm no biology major, but I was under the impression that the VNO still exists in humans but was no longer innervated... and a quick trip to Wikipedia suggests that I'm remembering correctly. That means it's at least conceivable that the VNO might have had other modes of interaction all along, e.g. hormonal, that continue to function in humans (though this is blatant speculation and not based on evidence). Certainly, some of the double-blind sweat scent studies suggest that humans might still picking out something.

@10: From what I recall, some genetics studies suggested that primates lost the primary function of the VNO not long after they gained color vision. In other words, our ancestors became sight-based rather than smell-based, so the VNO's pheromone-detection abilities were no longer actively selected for. (In fact, it's possible that losing the VNO was a net benefit, depending on whether fixation of the new allele was the result of positive selection or neutral drift followed by the founder effect. I don't recall off the top of my head which is the preferred explanation, or whether there were any bottlenecks during the relevant time in the primate family tree.)

@10: From what I recall, some genetics studies suggested that primates lost the primary function of the VNO not long after they gained color vision. In other words, our ancestors