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Pigs helped human smell evolve?

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File:A small cup of coffee.JPG The claim in the title of the science PR is How our sense of smell evolved, including in early humans

Most receptors can detect more than one smell, but one, called OR7D4, enables us to detect a very specific smell called androstenone, which is produced by pigs and is found in boar meat. People with different DNA sequences in the gene producing the OR7D4 receptor respond differently to this smell — some people find it foul, some sweet, and others cannot smell it at all. People’s responses to androstenone can be predicted by their OR7D4 DNA sequence, and vice versa.

Professor Cobb from The University of Manchester’s Faculty of Life Sciences and the other researchers studied the DNA that codes for OR7D4 from over 2,200 people from 43 populations around the world, many of them from indigenous groups. They found that different populations tend to have different gene sequences and therefore differ in their ability to smell this compound.

For example, they found that populations from Africa — where humans come from — tend to be able to smell it, while those from the northern hemisphere tend not to. This shows that when humans first evolved in Africa, they would have been able to detect this odour.

Interesting.  “For example, they found that populations from Africa — where humans come from — tend to be able to smell it, while those from the northern hemisphere tend not to.” What?

I (O’Leary for News) have lived all my life in the northern hemisphere and was advised never to try cooking boar meat in a conventional oven.

When I once broke the rule—among northern hemispherists (okay, a bunch of white people, if you insist on knowing, kin and similar)—the results were disastrous:

“Eeeww! WHAT is that awful smell?!! Open all the doors!!”

I threw all the pot contents out the back. Maybe raccoons ate it and died. I don’t care. Never broke the rule again.

Statistical analysis of the frequencies of the different forms of the OR7D4 gene from around the world suggested that the different forms of this gene might have been subject to natural selection.

Not, apparently, in Toronto in the early 1980s.

One possible explanation of this selection is that the inability to smell androstenone was involved in the domestication of pigs by our ancestors — andostroneone makes pork from uncastrated boars taste unpleasant to people who can smell it. Pigs were initially domesticated in Asia, where genes leading to a reduced sensitivity to androstenone have a high frequency.

My own ancestors survived for centuries, keeping pigs to pay the rent.

So this is what scientists have to front, to get attention to Darwin’s court-ordered theory today?

Here’s the abstract:

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, neither of which is shared with modern humans. 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. (paywall) – K. C. Hoover, O. Gokcumen, Z. Qureshy, E. Bruguera, A. Savangsuksa, M. Cobb, H. Matsunami. Global Survey of Variation in a Human Olfactory Receptor Gene Reveals Signatures of Non-Neutral Evolution. Chemical Senses, 2015; DOI: 10.1093/chemse/bjv030

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One Reply to “Pigs helped human smell evolve?

  1. 1
    Robert Byers says:

    Actually I say people have never smelled anything in our lives.
    Our souls don’t smell anything.
    what we do is observe a memory of smell. Smelling something is no different then remembering how something smells. Thats why we recognize smells. its in the memory. Since thats in the memory then it follows as a good option a recent smell goes straight into the memoru and we observe it.
    There are tests I;m sure that would show our smell turns off upon some triggering event.

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