Surroundings and Evolution Shape Human Sight, Smell and Taste

Amanda Melin’s study of the evolution of high-acuity color vision in primates informs how visual systems in primates and in humans adapt over time to the sensory landscapes both encounter. | Atlantic Photography 

Understanding how the five senses evolved can help inform how human sight, smell and taste continue to shift based on the environment, according to three researchers at the 2017 AAAS Annual Meeting in Boston.

We are currently experiencing “a state of mismatch” between the ways our senses evolved and our current surroundings, according to Kara C. Hoover, associate professor of anthropology at the University of Alaska, Fairbanks.

Our ancestors’ visual acuity evolved outside in the natural world, said Amanda Melin, assistant professor of anthropology and archeology and medical genetics at the University of Calgary. Yet, humans now spend significant amounts of time inside and this is adjusting our vision, she said.

“There’s mounting evidence that our anthropogenic light environments are having a real cost on our acuity,” said Melin, with rates of myopia – or nearsightedness – skyrocketing in recent years. While myopia does have a genetic component, evidence suggests that dark rooms, artificial lighting and “near-work tasks,” like staring at a computer screen or into a microscope, contribute as well.

Humans can correct nearsightedness with glasses, contact lenses or surgery, but myopia can put individuals at risk for other diseases such as glaucoma and retinal detachment, she said. Studies have shown that 40 minutes outside each day decreases chances of getting myopia between 25% and 50%, Melin said.

Yet the environmental changes wrought by human activity impact non-human primates as well, she said. Primates in general, even those that are nocturnal, are highly visually dependent. Sight drives nearly every aspect of their lives, including catching prey and communicating with other animals. In areas without light pollution, skies are actually getting darker due to pollutants and greenhouse gases in the atmosphere scattering light. Scientists do not know how non-human primates will cope with global darkening, Melin said.

Additionally, natural light even with its beneficial ability to lessen chances of acquiring myopia can be tainted with pollutants and less-than-fresh air can play with our sense of smell, Hoover said. The ability of humans to smell has adapted over time to aid survival and reproduction, helping humans identify nutritious foods, select partners and avoid spoiled food and other dangers, she said.

Much research has been done on our “smell-being,” particularly on how our environment continues to transform – and disrupt – our sense of smell, Hoover said. People in polluted environments have been found to have a diminished sense of smell, which will only become more common as the global population continues to urbanize, she said. 

Studies have shown the ability to detect smells can modify mental, social and physical health, but some people – those who live near factories or mining communities, for instance – are at greater risk of a diminished sense of smell and all of the attendant problems that can spark, she said. We are living in an age of “sensory inequities,” Hoover said.

“We’re not going to leave buildings, we’re not going to leave our computers, we’re not going to abandon that, so we need to actually create environments that engage us with the outdoors and also that, when we go outside, we’re not in a polluted space,” Hoover said.

Paul Breslin, professor of nutritional sciences at Rutgers University, has looked at our sense of taste to understand why we are drawn to certain flavors – and how taste preferences can harm or help our health.

Not every species loves sugar, but humans do – and so do apes, who are omnivores who love fruit and obtain about 80% of their calories from fruit, Breslin said. We’re also drawn to sour, acidic tastes, the other flavor present in fruit, he noted. Unlike other animals, humans and other primates have lost the gene that codes an enzyme to allow us to produce our own Vitamin C, likely because we were eating enough Vitamin C-rich fruit, he said.

To get these crucial nutrients and calories, other apes will go into a tree and gorge themselves on fruit until it’s gone. Humans do this, too, though metaphorically, Breslin said.

“We climb up into this tree that our society has created, and we gorge on the fruit, but the tree never runs out of fruit and we never come out of the tree,” Breslin said. “We have to keep in mind that we need to force ourselves down … periodically.”

Another type of food we are primed to prefer could help mitigate a persistent health problem and save lives, Breslin said. Humans are attracted to fermented food and drinks, including wine, beer, bread, fermented meats like pepperoni and fermented dairy like cheese and yogurt, he said. Properly fermented foods can promote a healthy gastrointestinal microbiome by delivering probiotics and prevent diarrheal diseases, the most common disease on the planet among humans and the second-largest killer of children, he said.

“I believe that if we eat more fermented foods we’ll be able to have a positive impact on helping prevent and treat this,” said Breslin.

[Associated image: Amanda Melin]