A Conversation with Dr. Kara Hoover On Uncovering the Evolution of Our Sense of Smell

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By: Alex Pierce-Feldmeyer

“I have a lot of happy smell memories. I suppose an abiding one is pipe smoke… I associate that to summers in West Virginia, my grandfather taking me on long walks along the railway. Sometimes my father would come along and we’d hunt among the rocks for fossils.”

It was my pleasure to converse with Dr. Kara C. Hoover, a biological anthropologist who is interested in enhancing our understanding of the ancient and current human sense of smell.

Hoover initially wanted to be a paleontologist, influenced at an early age by her geologist father. Both Hoover and her father were meticulous, but eventually, Hoover found herself drawn to the reconstruction of prehistoric biology with animal bones and teeth. And more recently, it is the prehistoric utility of our sense of smell that currently drives Hoover’s interest in the evolution of olfaction, as well as its ties to emotions and memory.

Where Hoover’s Journey to the Nose Began

Hoover attended Flagler, a liberal arts college in St. Augustine, Florida, majoring in social sciences, with a concentration in history. Starting at a liberal arts school made it harder to dive deeper into science at an early stage in her life, but Hoover persisted. She obtained two Master’s degrees, one in religion and another in anthropology from Florida State University. Finally, she attended Southern Illinois University and graduated with a Ph.D. in Anthropology.

 

Did She Find Olfactory Science or Did the Science Find Her?

Early in Hoover’s career, she visited Japan to study how hunter-gatherer populations survived when food was scarce. When a community is specialized in one form of living (e.g. fishing) but coastlines recede and fishing is no longer the primary way to hunt, how do these populations survive? What made these populations resilient? These questions were seeds that bloomed into endless questions and stimulated Hoover’s curiosity. She began to wonder how prehistoric populations knew what to eat when they were forced to change their lifestyle. Was it a sense of smell that helped them survive when under duress? Was it women’s enhanced ability to smell, which helped find food, that facilitated population maintenance1,2? These curiosities led Hoover to begin to hypothesize that sensory systems—specifically smell and its relationship with emotion and memory, aided the survival of prehistoric humans. Hoover believes olfaction is key to understanding early human resilience, because finding enough food meant reproductive success and proliferation.

As a visiting professor at Emory University, Hoover lectured on evolutionary anthropology. She approached this topic by examining each system of the body and its evolution within the primate lineage. She explored derived traits unique to humans and our closest relatives. Hoover was, again, especially intrigued by the human sense of smell, particularly with how odors may be perceived without conscious awareness or higher brain processes. She was further perplexed by how odors evoke memories and emotions (for more about smell, memory, and emotions, click here, here and here).

These qualities that make this sensory system particularly ancient suggested to Hoover that smell could play an essential role in human adaptation during the early migrations out of Africa. Migrations were challenging journeys, and it is possible our nose could have played a role in helping humans subsist.

 

Carving Her Niche

Hoover began building a lab when she accepted a position at the University of Alaska Fairbanks, as a biological anthropologist. Her research focused on “human sense of smell and the factors that shaped its evolutionary tuning as well as the modern distribution of variation in human populations…also links between smell and food preference/subsistence and evolutionary mismatches in modern environments.” 3

Following Hoover’s career trajectory, her organically formed research path was the product of following the questions that were and are most passionate to her.

She even admits “it wasn’t what I thought I would be doing. I was initially very interested in understanding how genetic variation in olfactory receptors shaped population preferences in odors, ultimately foods.”

Before researching these questions, however, Hoover believed there was and still is more fundamental research that needs to be performed first. Sensory ecology has focused primarily on vision, but Hoover wants to focus more on the role of smell. One of her goals is to disrupt the notion that smell is not as useful as other senses.4

Hoover also served as a visiting researcher at the Max Planck Institute for Evolutionary Anthropology. It was here that Hoover’s first foray into olfactory receptor research began. She wants to understand if evolutionary forces acted to shape the current distribution of human variation in olfactory receptor genes.

Hoover also puts forward the idea that there is likely ecological context affecting genetic variation in sensory abilities. The interaction of organisms and their environment may have exerted selective pressures on the population towards specific food odors, which could still be genetically present today and help explain variation in peoples’ diets5. This is particularly interesting when you think about the diverse regional differences in diet staples and meal times. For example, consider the carbohydrate emphasis in many South African diets compared to the higher consumption of fatty acids in the Mediterranean populations.

Before defining those relationships, Hoover needed to understand if humans were unique. Research suggests that olfactory receptor lineages diverged. One way to understand these differences is to study humans compared to extinct humans like Neandertals6.  Hoover and her collaborators are finishing up a project that has attempted to reconstruct how our extinct relatives responded to odors—do they smell things the same way as we do? Hoover’s next project is to explore Hadza hunter-gatherers in Tanzania.

Hoover and collaborators hope to learn about the Hadzas’ enriched sense of smell7 and how it may affect their diet, behavior, and culture. She also hopes to map genes onto smell ability to further understand genetic distinctions in true olfactory ability. This may also help researchers uncover how a smell-scape (surrounding environment) affects genetic distinction in olfactory function.

This area of work brings up the question of whether our daily environment (working in buildings or fighting fires, for example) affects the evolution of our sense of smell and thus our perception of foods, the environment, and our behavior. Studying the genes of the Hadza population could reflect what prehistoric human olfactory adaptations may have been like and help us understand how similar or different we are to our ancestors now.

 

What Methods Can a Biological Anthropologist Use to Answer Questions About Prehistory?

Mainly:

  1. Archaeology
  2. Climate Reconstruction
  3. Osteology and Dental Anthropology
  4. Genetics

Hoover describes biological anthropology as a “contextual field of inquiry” where biology is the main focus, paired to the cultural environment created for ourselves and the ecology in which we live.

And in Hoover’s words,

 “We can engage in some ethnography to make sense of our interpretations of the past by looking at closely related local descendent populations or populations that share a similar profile. Ultimately, through the combination of understanding how the bones that support the olfactory system have changed over time in response to ecological factors and how the genes have changed over time due to ecology, behavior, migration, and admixture, we can understand the journey taken to reach our current location in the evolutionary context. As for the receptors, we can use the paleogenomes of extinct hominins as a template to make a living replica of their receptor, which can then be functionally tested and compared to other data.” Paleogenomics is based on the reconstruction and analysis of genomic information in extinct species.8

This description is reminiscent of the sensory experiences of eating. We are physiologically sensing taste and flavor but perceptions are manipulated via environment, expectations and so much more. When we eat, there are equal parts of biology and culture/environment incorporated into any consumption experience.

 

The Role of Smell and What Happens When You Lose It

Hoover’s primary interest is in olfaction. Therefore, I thought it was pertinent to discuss anosmia as it relates so much to perceptions of flavor and ultimately eating behavior. But as you’ll realize, Hoover explains that anosmia affects much more than eating behaviors.

 Even with the tremendous boom in olfactory research in the past two decades, there are some problems that we are far from being able to solve with our current knowledge.”

She points out that, “We have not tracked the clinical incidence of dysfunction—probably partly because there has been a lack of appreciation for the significance of smell to physical, mental and social health, and partly because we have no cure for dysfunction.” She further comments on the fact that the rate of blindness is less than that of anosmia. Hoover seems to think the combination of an underestimation of olfaction’s role in health, the lack of data and the complexity of the olfactory system slow the progress of olfactory research.

 “The olfactory system is seemingly more complex and mysterious than other senses—probably because chemosensing (taste and smell) are ancient senses, perhaps the most ancient.”

She underscores her point claiming, “The average person underrates their sense of smell.” This is what perhaps intrigued Hoover from the beginning. Smell plays critical roles in peoples’ social lives. There are even studies that support the notion that if you are a better smeller, you have a larger social network which has been proven for women2.

 “Humans are primates, the most social perhaps of all mammals. Learning social hierarchies (and our place in them) poses cognitive development challenges in childhood and become increasingly important to maintain in adulthood. We have very few robust studies on human pheromones let alone odor-guided behavior, but we anecdotally can relate to ‘knowing’ something without seeing it—such as fear which has been shown to be chemically transmitted in humans9,10. We avoid, like/dislike, are suspicious of, and trusting of others for often inexplicable reasons—just as we have intense chemical attractions to and repulsions by individuals that we know are chemical.”

Hoover ends with the true detriments of neglecting the seriousness of the loss of smell, commenting on mental health problems like depression and anxiety, as well as the physical, like weight gain or loss, malnutrition and metabolic disruptions.

For something that seems like its purpose is to merely help us experience the world of flavor, there is far more in life lost with an impaired sense of smell.

 

For the Time Being…

Hoover ultimately hopes to gain knowledge on the potential of our surroundings, culture and environment, to enact selective pressure on our sense of smell, selective pressure being anything that influences evolution. Uncovering this knowledge could mean discovering differences in the role of smell between prehistoric humans and us.

Hoover is quick to add that she believes genetic selection (genes changing over time) may not mean smell has become less critical. She thinks having fewer genes could mean they are dual functioning, and more efficient than previous lineages. However, it may also be that we find we are actually not that different from our ancestors after all.

 

Bonus Questions with Dr. Kara Hoover:

 What can we expect for the future of smell?

“Branding with smell and using smell to manipulate consumers are related marketing trends—either link a bespoke odor to a luxury brand (hotels, cars) or use an odor that has common emotional outcomes to set a tone for consumerism. More museums are integrating or attempting to incorporate smell into exhibits and airlines are starting to integrate smell clocks into long haul flights to aid with jet lag.

There is no denying the race to incorporate odors into the internet is real—online porn and gaming are driving much of the demand I think—the fantasy is more real in a virtual reality that goes beyond visual immersion. Whoever cracks the problem of odor diffusion and overcomes the limits of the number of odors dispensed (like a color palette for smells) will be a billionaire.”

 What further gaps in knowledge are you most interested in?

“I suppose a big gap is: What makes for superior olfactory performance? We know that women are better at learning odors and thus better able to identify them, but we aren’t clear if that is a language and/or perception issue or something biological at the receptor or olfactory bulb level. Plus, even if we knew what every single active olfactory receptor is capable of binding, that would not explain the almost infinite number of odors we can smell. Clearly, 400-450 receptors (even with some much more generalized than others) cannot explain the vast number of odors we are capable of detecting. I mention this because the process of smelling starts with binding the odorant.

Speaking of that, we aren’t entirely sure of what odorant-binding proteins do nor how volatile compounds enter an aqueous system.”

Sensing and perceiving smell begins with aroma molecules interacting with the olfactory epithelium that then stimulate olfactory receptor cells to send signals to your brain. This messaging tract also hits other parts of the brain, enabling associations with smells to be learned.

For more on the olfactory tract, watch this video.

Do you have a favorite smell?

“Cherry vanilla pipe tobacco like my grandfather used to smoke—the combination of earthiness, wood, sweet, and fruity is a powerful combination of contrasting smells. I prefer contrasts to complements and that goes for food too. One of my current favorite scents is Jo Malone’s Bronze Wood and Leather—I sometimes layer that with [Joe Malone] Ginger Biscuit.

Last fall on a research trip to Bologna Italy, I fell in love with Comptoir sud Pacifique’s Rhum et Tabac. On that same trip, I fell for lemon tortellini—the fats of the pasta and cream with the sour and bitter of the lemon was amazing—especially paired with deep tannic wines that smell of barnyard floors, earth, tobacco, and must.

I’ve been told by a chef that I have a very aggressive palate!

Thank you for sharing Dr. Hoover!

 

References:

  1. Larsson, M., D. Finkel, and N. L. Pedersen. 2000. “Odor Identification: Influences of Age, Gender, Cognition, and Personality.” Journals of Gerontology – Series B Psychological Sciences and Social Sciences 55 (5): 304–10. https://doi.org/10.1093/geronb/55.5.P304
  2. Boesveldt, Sanne, Jason R. Yee, Martha K. McClintock, and Johan N. Lundström. 2017. “Olfactory Function and the Social Lives of Older Adults: A Matter of Sex.” Scientific Reports 7 (February): 1–6. https://doi.org/10.1038/srep45118
  3. https://www.uaf.edu/anthro/people/faculty/hoover/
  4. https://smellofevolution.com/about/
  5. Hayden, Sara, et al. “A cluster of olfactory receptor genes linked to frugivory in bats.” Molecular biology and evolution4 (2014): 917-927..
  6. .O’Bleness, Majesta; Searles, Veronica; Varki, Ajit; Gagneux, Pascal and Sikela, James M. 2014. “Evolution of Genetic and Genomic Features Unique to the Human Lineage” 13 (12): 853–66. https://doi.org/10.1038/nrg3336.Evolution
  7. Lachance, Joseph, Benjamin Vernot, Clara C. Elbers, Bart Ferwerda, Alain Froment, Jean Marie Bodo, Godfrey Lema, et al. 2012. “Evolutionary History and Adaptation from High-Coverage Whole-Genome Sequences of Diverse African Hunter-Gatherers.” Cell 150 (3): 457–69. https://doi.org/10.1016/j.cell.2012.07.009.
  8. https://en.wikipedia.org/wiki/Paleogenomics
  9. Ackerl, Kerstin, Michaela Atzmueller, and Karl Grammer. “The scent of fear.” Neuroendocrinology Letters 23.2 (2002): 79-84.
  10. Albrecht, Jessica, et al. “Smelling chemosensory signals of males in anxious versus nonanxious condition increases state anxiety of female subjects.” Chemical senses 36.1 (2010): 19-27

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