Tag Archives: olfaction

Smelling in the Wild

With colleague Dr. Colette Berbesque (University of Roehampton), I am about to start two exciting new projects that focus on the human sense of smell in natural environments.

One project will focus on how our sense of smell may be influenced by subsistence. Our project is a corollary study to work by the Sorokowskas and co-workers (here and here) that argue for a relationship between odor acuity and discrimination relative to diet. We are interested in testing the hypothesis controlling for ecology (the other studies used disparate populations which introduced other explanatory variables) and genetics.

The other project will focus on how our sense of smell is influenced by modern living. My work on sensory inequities and our sense of smell in jeopardy were featured in the news media this past year (see here and here and here) and on radio (BBC Radio 5, BBC Radio Ulster, Dermot and Dave on Today FM Ireland, and Talk Radio Ireland) and form a platform for this project that generates supportive empirical data. We are interested in understanding how the human sense of smell is affected by modern living and how well-being is impacted by environmental effects.

Stay tuned at Smelling in the Wild for details of our upcoming pop-up pilot studies and how to get involved!!

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Filed under Anthropology and Evolution, Evolutionary ecology, Olfaction, primate social life, Senses, Sensory ecology, sensory inequities, Smelling in the wild, stress, Uncategorized, urban-rural, Well-being

The chirality of smell



As I prepare the first half of my Science of Smell online class, I am having fun looking for various examples of all things biomolecular, biochemical, and genetic related to olfaction. If I were a taste and flavour chemist or a molecular gastronomist, I’d probably be interested in somehow exploiting the chirality of biomolecules in food and drinks!

Chirality refers to the non-symmetrical nature of some molecules. Non-symmetrical molecules are like our right and left hands: they appear the same in reverse but you cannot superimpose the image of one over the other in the mirror nor can a left-handed glove fit a right hand. In the pharmaceutical industry, chirality is very important because the enantiomer of a biomolecule that produces a positive outcome (like reducing morning sickness using thalidomide or hyperactivity using Ritalin) may cause a harmful effect (birth defects) or no effect. The handedness is determined by the stereocenter of a molecular. Those with ‘right’ handed stereocenters are ‘R’ or + enantiomers and those with ‘left’ handed stereocenters are ‘S’ or – enantiomers (the S comes from sinister, Latin for left).

Our olfactory receptors are clever things: they can tell the difference between the right and left hands! The two most common examples are of carvone and limonene.  The R-carvone/(-) carvone is recognized as mint and its enantiomer as carraway. R-limonene/(+) limonene smells ‘orange’ and its enantiomer is lemon (see image to the right). So next time you smell oranges and lemons at the same time, recognize the power of your nose to be ambidextrous by distinguishing between the two biomolecules!

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Filed under Food, Olfaction, Science, Senses, smell of the week

Inhale for health

This research is a bit old (October 2013) but recently caught my eye:

Research out of Japan shows that walking in the woods also may play a role in fighting cancer. Plants emit a chemical called phytoncides that protects them from rotting and insects. When people breathe it in, there is an increase in the level of “natural killer” cells, which are part of a person’s immune response to cancer.

“When we walk in a forest or park, our levels of white blood cells increase and it also lowers our pulse rate, blood pressure and level of the stress hormone cortisol,” Michelfelder said.

There is rare evidence of cancer (osteocarcanoma) in prehistoric hunter-gatherer populations (see here for a nice public science summary) and mummies (another public science review is found here). This may be because we can’t detect it and accurately determine its frequency. Modern techniques like CT scanning make inroads into non-invasive paleopathology data gathering but skeletons have a limited capacity to reveal diseases of the past. This is partly because the lesions (like most pathologies) often don’t reach the bones, take too long to reach the bones before death, or are nonspecific.

The rarity of evidence for cancer may also be because it simply wasn’t there. Most cancers occur at the end of of or after reproductive years; the shorter human life span ‘in the wild’ would likely lead to fewer cases of cancer experienced by our prehistoric relatives and not impact net reproductive success (meaning any cancer-causing genes would persist in human populations). Persistent cancer-causing genes interact with the modern environment and longer life span to reach modern cancer frequencies. I wonder if lifestyles that take one into the woods for significant periods of time (e.g., prehistoric hunter-gatherers, modern populations leading ‘traditional’ lifestyles) reduce cancer incidence?

I am reminded of something I heard when I was a kid about the actor Dirk Benedict (from Battlestar Galactica–the original Starbuck!–and the A-Team) having had overcome prostate cancer by disappearing into the woods and the wilds of the country and eating a macrobiotic diet. I looked up his story to see if I remembered correctly. I had mostly:

When I learned I had a tumor—I refused to be tested for malignancy—I weighed 180 pounds. When I came out of the mountains of New Hampshire six weeks later, I weighed 155. I went to stay in a friend’s cabin because I didn’t want any distractions, any temptations, anybody calling up to say, “Let’s go have a bagel.” Well, all hell broke loose. Some days I felt on top of the world, and other days I couldn’t get out of bed. Sometimes I couldn’t walk up the stairs, and sometimes I’d ride, run and chop wood for 24 hours.

I never did go into a hospital. Instead, I packed up my duffel bag and became a vagabond, traveling to Montana, Maine, California, New York City, Wisconsin, hitchhiking across the country once and driving across twice.

Did the woods help? Maybe! The sense of smell–yet another benefit!

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Filed under Anthropology and Evolution, Olfaction, Senses, Uncategorized

Is there a connection between dietary repetition and food preferences?

A Science News Post (brought to my attention earlier in the summer by @elizabethjrowe) presents research trends in food science: the pairing of retronasal olfaction and taste reception in studying flavour and the knowledge pairing of culinary experts and scientists within a relatively new journal Flavour. I am glad that food sensation (for lack of a better word to describe the complex process of perception, taste, smell, hedonic value, and preference) is getting increasing amounts of attention! From an anthropological perspective, however, the evolutionary and cultural underpinnings of these studies is still missing from the dialogue–something I hope to rectify in the coming years!

The article leans towards the idea that repetition is the driver of food preference–and it starts in the womb. Support for this idea is presented by referencing the study on babies whose mothers ate anise and garlic during pregnancy (and therefore were not averse to the odors post-natally).  I assume the reference is to Schaal et al. 2000. That paper was great and is a start to exploring cross-cultural differences in the interaction between odor perception and food preference–but there also might be variation in olfactory receptors within the sample from the Alsace region (where anise is a common food additive but the population history of which is complex).

A taste and smell scientist is quoted as supporting the idea of repetition shaping diet: “What makes lasagna loved is that the odors have been paired to a source of calories.” Odors stimulate appetite but arguing for a causative relationship among odors, loving a food, and its caloric value is premature. We have so much yet to learn about the genetic architecture of individual and population odor profiles, which ligands bind to which receptors, odor processing, perception, and consciousness let along variation among all these things. All these known unknowns make olfaction a great place to work (and the unknown unknowns exciting things to be discovered)!

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Filed under anthropology, Food, Olfaction, Senses

The piggy smell of Eurasian genetic landscapes

Between 6000-4000 years ago (according to study published in Nature Communications), indigenous Mesolithic hunter-gatherers acquired pigs from Neolithic farmers immigrating to Europe. I have been interested in Pleistocene pigs for a while (and their continued association with humans into the Holocene). The reason for my interest is that pigs produce a lot of androstenone (a sex steroid), especially males, and humans vary in their genotypic/phenotypic perception of androstenone.

Human variation in androstenone perception depends on two non synonymous SNPs (Keller et al. 2007), R88W and T133M. These SNPs appear to play a role in meat preference: Lunde et al. (2012) found that wild type humans (RT/RT) rated the meat of non-castrated male pigs less favorably than those with variant alleles (RT/WM and WM/WM). HapMap and 1000 Genomes are great resources but do not capture the variation local human populations, let alone the anthropological underpinnings of variation. In my lab and using a wide mix of global human populations, I found significant variation in androstenone perception frequencies, with higher frequencies of mutations throughout Eurasia–an area heavily invested in pig meat throughout human prehistory; in Japanese and Northern Europeans, the frequency of homozygote recessive mutations is much higher and these areas have a rich history with pigs–especially Japan.

Currently, I am working through the archaeological data for human-pig interaction in Europe and Asia (with a special focus on Asia as the origin of all pigs–see here and here for starting places) to interpret the results of the genetic data. Both the archaeological data and genetic data are thin when taken across such a huge space but they are a starting point; a neat study would be to find a locale with a rich archaeological record, human population to test for the gene and perception, and a good ethnohistory on the relationship with pigs–something I am working on right now.

Combining data from the archaeological record and the genetic history of human populations adds depth to what could, on their own, be interesting but uncontextual datasets. Taken together, these datasets can paint a more detailed picture of the evolutionary inter-relationship between genes and diet.

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Filed under Analysis, anthropology, Anthropology and Evolution, Food, Olfaction, Senses

Detecting stress via feces?

Noted smell scientist Avery Gilbert blogged about a team of Japanese scientists who tested what quantitative differences are there in the odor profiles of mice experiencing different life conditions (e.g., no bedding, fasting). What they found is that the greater the stressful life conditions, the stronger the smell of the feces. Seventeen odor compounds were identified  (aldehydes, sulfides, isobutryric acid…). The ‘shelf-life’ of these compounds in feces is beyond my chemical knowledge but if the ‘stress’ evidence from feces could be operationalized some way, we would have a great way of examining ancient coprolites (from dinosaurs to humans) for evidence of stress as yet another line of evidence in reconstructing past life conditions!

**Incidentally, when my blog spell check highlighted coprolite and I looked to see what other spelling options were available, the first listed was profiterole! If you know what a coprolite is or figure it out contextually, you can better appreciate the irony!

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Filed under Bioarchaeology, Olfaction

The complexity of taste!

A recent blog on how the loss of sense of smell can intensify taste makes some interesting points. The two that have interested me for a while are the contribution of trigeminal nerve sensations to consumption (for lack of a better word) and the hazy area of taste (if we get into the murkier ion channeling side of things).


The touch sensations reported at the end of the blog (e.g., creaminess, dryness of tannins) that may be intensified with loss of smell are not actually taste/tastebud related.  There are three nerves sending information to the brain from the tongue that comprise the gustatory system (vagus, glossopharyngeal [innervate TAS1R andTAS2R], and facial nerve [chorda tympani branch innervates the TAS1R and TAS2R taste receptors]. The trigeminal nerve also plays a strong role (falsely reporting the burn in chili or the cool in fats and methols etc). Personally, I am driven by my nose and trigeminal nerve. I love intense experiences like chili peppers, wasabi, and methol but I dislike spongy or slimy experiences like mushrooms or okra (respectively and sometimes both for mushrooms!). Oddly and despite my dislike for other fungi, I do like truffles but have only ever eaten them in France (so infrequently at best!). The olfactory system alone is complicated enough without adding taste to make flavour let alone adding touch to make texture/sensation. But, perhaps we need to think more about this when it comes to food taste and preferences. If someone dislikes eating a food, will that same person report disliking its smell because of the association with an unpleasant trigeminal (touch) experience?

Taste is under-rated and for a reason due to its minimalistic suite of traits. Taste may be more complicated if we push beyond the five basics by first considering detection methods: salty and sour are detected through ion channels while sweet, bitter, and umami detected through G protein-coupled taste receptors (same type of receptor used in olfaction). Salt and sour may eventually be found to have receptors associated with them as well (sour is ahead of salt in evidence right now several possible candidate genes).*

The complex mechanism of sugar detection may also explain why creating an artificial sweetener that tastes natural is so difficult; specifically blame it on one of three receptors involved in sugar detection, TAS1R3. A 2012 study on taste receptor evolution suggests the importance of dietary niche in the structure and function of an animal’s sensory system:

tet cookie

•Repeated and independent loss of function in TAS12R in Carnivores throughout evolution (but why does my blue cat love sweets and my tabby steal cookies!?)•Sweet and umami receptor genes were nonfunctional in two sea mammals (dolphins  also had nonfunctional bitter taste receptor genes) and have a diminished sense of taste; in unrelated studies, olfaction is also odd in sea mammals b/c they lost then regained some Class 1 olfactory genes (those that detect water-borne odors).

Champagne cocktail: note wide mouth flute for smelling the drink while drinking!

Bitter is a good one too. There are multiple TAS2Rs expressed in one taste receptor cell which raises the question: can mammals distinguish between the tastes of different bitter ligands?  There are many more bitter compounds than we have receptors for–combinatorial coding like olfaction? I personally love bitter (but not all types of bitter) and will often take a classic champagne cocktail (but without the sugar lump).

While I will always take smell over taste, I am excited about the future taste research and also more work on the involvement of facial nerves (especially the trigeminal nerve!).

*DOI:10.1038/35098087, DOI:10.1126/stke.3492006tw292, DOI:10.1046/j.0022-7722.2003.00062.x, PNAS 103 (33): 12569-12574

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