Tag Archives: smell

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

Smelling in the polar vortex

Since so many parts of the US (mainly the Great Plains, mid-west, and parts of the northeast) are experiencing normal interior Alaska winter temperatures right now, I thought I’d write about what/if we smell when it gets cold.

Our ability to smell things is related to temperature because temperature is a key factor in volatility (tendency to vaporize). We tend to smell volatile compounds (those with high vapor pressure at normal temperatures) that have molecular weights below 300 daltons. Volatiles with lower molecular mass tend to have lower boiling points and evaporate and diffuse more rapidly than compounds with high molecular masses. For example, ethanol (pure alcohol) has a mass of 46 daltons and will vaporize and diffuse at a lower temperature and more rapidly than indole (a fecal smelling element often added to jasmine perfumes to produce a musky scent) which has a mass of 117 daltons.

2009

Ice fog in Fairbanks

Boiling is one end of the vaporization extreme and freezing is the other. The freezing point of water is 0 but other molecules have lower thresholds–however, even if a molecule isn’t frozen, the colder it is, the less thermal energy it will have and its volatility will be reduced (think  of how the aroma of cooled food is not as strong when it was hot). When temperatures are extremely cold, the sense of smell is de facto eliminated (even if your nose weren’t blocked by anti-frostbite protective gear like balaclavas). During the winter in Fairbanks, the only things you can reliably smell outside (down to a certain temperature) are wood burning stoves and car exhaust pollution–both in heavy concentrations trapped close to the ground due to temperature inversion. Maybe another reason we like hot bevvies during cold weather is the welcome rush of volatiles!

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The evolution of the mammalian brain starts with smelling!

A study of CT scans of two early Jurassic period mammals reveals the brain evolution had three stages, the first of which was driven by olfaction. To read the original, go here. The next stage is characterized by an increase in tactile sensitivity from body hair and the third stage by skilled muscle movement using the senses (neuromuscular coordination).

Olfaction is different from the other senses in that every time we inhale, we detect odors whether we want to or not. Even mouth-breathing will not prevent detection of odors. A study from 2007 finds that there is a biological explanation for this: olfaction neurons are stimulated by both mechanical (air from respiration) and chemical (odors) stimuli.  In the words of the authors from this study:

The mechanosensitivity of our olfactory neurons has two possible functions, suggest the investigators. The first is that it increases our ability to smell, enhancing the detection of odorous molecules in the air. The second is a peripheral drive in the brain to synchronize rhythmic activity, which is the concurrent firing of neurons in the olfactory bulb with breathing.

“The mechanosensitivity may increase the sensitivity of our nose, especially when stimulated by weak odors,” says Ma. “It helps the brain make better sense out of odor responses when it integrates airflow information. We still don’t know how it happens, but sniffing is essential for odor perception.”

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Filed under Anthropology and Evolution, Olfaction

Making scents of tea olives

The tea olive Osmanthus fragrans is a wonderfully aromatic plant, particularly when its scent is captured by the evening breeze. I have been stopped in my tracks upon detecting this olfactory ambrosia in the air. What amazes me is that some people cannot smell it at all or only can detect the slightest ghost of a scent.

Each of us has a unique olfactory repertoire that is genetically controlled and reflects an evolutionary heritage. In my family, my father and I can smell the tea olive but my mother cannot, nor can my boyfriend. My mother and boyfriend have genetic histories tied to the British Isles on both sides of their families across multiple generations. So, while I share in this heritage via my mother, I also share my father’s genetic heritage, which is half Croatian. He and I share certain physical traits that are sometimes associated more with Asian populations. This reflects the fact that Eastern and Central Europe were part of a geo-genetic pathway between Asia and western Europe in recent human evolution (circa 100,000-45,000 years ago). For a few genetic maps, see here and here.

How does this relate to the tea olive? Well, its origins are Asian. In China it has been cultivated for thousands of years and the varieties there are far more aromatic than the ones we find in the US today. If our olfactory repertoires are the product of continuous adaptation to the environment, we can assume that specific odors are more powerful to some than to others by sheer nature of evolutionary heritage. Thus, if Asian populations exploited the tea olive as a resource throughout recent evolution, the ability to detect the tea olive via olfactory pathways would increase via selection for more receptors that detect this particular molecule. In populations other populations, those receptors would not be selected for and would remain at a lower frequency, or be absent altogether. This results in those people having only a minor ability to detect the scent in high concentrations, if at all.

For those of us that can detect this scent, Asian heritage or not, we’re lucky to have those receptors!

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Filed under Anthropology and Evolution, Olfaction, Senses