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Allelic variation at 4 loci in the human olfactory receptor gene OR7D4 is associated with perceptual variation in the sex steroid-derived odorants, androstenone, and androstadienone. Androstadienone has been linked with chemosensory identification whereas androstenone makes pork from uncastrated pigs distasteful ("boar taint"). In a sample of 2224 individuals from 43 populations, we identified 45 OR7D4 single nucleotide polymorphisms. Coalescent modeling of frequency-site-spectrum-based statistics identified significant deviation from neutrality in human OR7D4; individual populations with statistically significant deviations from neutrality include Gujarati, Beijing Han, Great Britain, Iberia, and Puerto Rico. Analysis of molecular variation values indicated statistically significant population differentiation driven mainly by the 4 alleles associated with androstenone perception variation; however, fixation values were low suggesting that genetic structure may not have played a strong role in creating these group divisions. We also studied OR7D4 in the genomes of extinct members of the human lineage: Altai Neandertal and Denisovan. No variants were identified in Altai but 2 were in Denisova, one of which is shared by modern humans and one of which is novel. A functional test of modern human and a synthesized mutant Denisova OR7D4 indicated no statistically significant difference in responses to androstenone between the 2 species. Our results suggest non-neutral evolution for an olfactory receptor gene., (© The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Olfactory receptors are a specialized set of receptor cells responsible for the detection of odors. These cells are G protein-coupled receptors and expressed in the cell membranes of olfactory sensory neurons. Once a cell is activated by a ligand, it initiates a signal transduction cascade that produces a nerve impulse to the brain where odor perception is processed. Vertebrate olfactory evolution is characterized by birth-and-death events, a special case of the stochastic continuous time Markov process. Vertebrate fish have three general types of receptor cells (two dedicated to pheromones). Terrestrial animals have different epithelial biology due to the specialized adaptation to detecting airborne odors. Two general classes of olfactory receptor gene reflect the vertebrate marine heritage (Class I) and the derived amphibian, reptile, and mammal terrestrial heritage (Class II). While we know much about olfactory receptor cells, there are still areas where our knowledge is insufficient, such as intra-individual diversity throughout the life time, epigenetic processes acting on olfactory receptors, and association of ligands to specific cells.

The olfactory receptor gene family is the largest in the mammalian genome (and larger than any other gene family in any other species), comprising 1% of genes. Beginning with a genetic radiation in reptiles roughly 200 million years ago, terrestrial vertebrates can detect millions of odorants. Each species has an olfactory repertoire unique to the genetic makeup of that species. The human olfactory repertoire is quite diverse. Contrary to erroneously reported estimates, humans can detect millions of airborne odorants (volatiles) in quite small concentrations. We exhibit tremendous variation in our genes that control the receptors in our olfactory epithelium, and this may relate to variation in cross-cultural perception of and preference for odors. With age, humans experience differential olfactory dysfunction, with some odors remaining strong and others becoming increasingly faint. Olfactory dysfunction has been pathologically linked to depression and quality of life issues, neurodegenerative disorders, adult and childhood obesity, and decreased nutrition in elderly females. Human pheromones, a controversial subject, seem to be a natural phenomenon, with a small number identified in clinical studies. The consumer product industry (perfumes, food and beverage, and pesticides) devotes billions of dollars each year supporting olfactory research in an effort to enhance product design and marketing. With so many intersecting areas of research, anthropology has a tremendous contribution to make to this growing body of work that crosses traditional disciplinary lines and has a clear applied component. Also, anthropology could benefit from considering the power of the olfactory system in memory, behavioral and social cues, evolutionary history, mate choice, food decisions, and overall health., (Copyright © 2010 Wiley-Liss, Inc.)