The nose knows
The paper on the ability of humans to track smells contained a couple interesting references on the human specific loss of some olfactory genes (see an old post here for an interesting correlation between the loss of these genes and the rise of color vision). Apparently, some genes have both functional and non-functional versions that still segregate within the population. So do different populations have receptors for different scents?
The last link is to a paper that typed 51 olfactory receptor genes in 189 people. It’s a little unclear where these 189 people come from (though they do refer to African-Americans, so it’s apparently a sample of Americans); it would be interesting to type them in a large number of populations (the human diversity panel, perhaps?) and give that hypothesis a whirl.
However, see this paper for an argument that humans actually have a pretty good sense of smell, and some possible explanations for why the loss of olfactory receptors doesn’t mean the loss of the sense:
[M]uch of the olfactory system can be removed with no effect on smell perception. The olfactory receptor genes map topographically onto the first relay station, a sheet of modules called glomeruli in the olfactory bulb. Up to 80% of the glomerular layer in the rat can be removed without significant effect on olfactory detection and discrimination. If the remaining 20% of the glomeruli-and the olfactory receptor genes they represent-can subserve the functions of 1,100 genes, it implies that 350 genes in the human are more than enough to smell as well as a mouse.
Not really on topic, but checking out the star-nosed mole’s olfactory apparatus is well worth it. There have been a number of breakthroughs recently in star-nosed studies: recently, how they can smell underwater, but awhile back also stuff about how thir brain is wired. Their weirdness is biologically interesting; they really are unique creatures.
So do different populations have receptors for different scents?
journals.org/perlserv/?request=slideshow&type=table&doi=10.1371/journal.pbio.0040072&id=6202
Probably — the Voight et al PLoS paper on recent selection found that the gene ontology categories of “chemosensory perception” and “olfaction” were both under selection in Europeans & Africans but not Asians.
http://biology.plos
Underwater sense of smell
Very fast reaction time
The star-nosed mole is top dog. It can identify and eat a piece of prey in 120 milliseconds.
I have done quite some reading about the superfamily of G protein-coupled receptors (GPCRs), which includes the olfactory receptors as well as most of the other receptors for small molecules. I was very surprised the first time I found out that about half of all human GPCRs are olfactory. Given our reputation for an incredibly degenerated sense of smell, along with our complex nervous and immune systems, I would have thought that fraction to be much lower.
Our immune systems aren’t notably more complex than most other mammals’, and our complex nervous system is only unusually complex in the higher levels of implementation. Olfaction requires far more complexity than neural signaling, which only involves maybe a few thousand neurotransmitter types.