by If you walk through a forest and pass a beehive, you may smell the sweet scent of honey on the wind and suddenly be flooded with memories: having tea with grandma or eating warm biscuits on a Sunday morning.
If you were taking that walk 300,000 years ago with a Denisovan — a now-extinct hominid closely related to Homo sapiens and first discovered in 2010 — when you smelled the honey, your companion may have already climbed the tree for a sugary treat.
That’s because Denisovans appear to have been particularly sensitive to sweet smells like honey or vanilla, suggests new research published in the journal iScience in January. This may have helped them find food. Meanwhile, a group of a related species, the Neanderthals, developed a mutation that could have spared them the smell of their own body odors.
Humans have a lot of genetic diversity in our olfactory receptors, which govern smell, allowing us to detect a huge range of scents. Researchers think it helped humans adapt to new environments as they spread across the globe, sniffing out new foods and new predators.
It’s a popular idea that humans have a poor sense of smell, compared to dogs, for example. But dogs live in the world so differently that the comparison might not mean much. Understanding our earliest relatives – the other Homo species that migrated from Africa with us – can offer a better context for our sense of smell and give us a sense of life at our origins.
Researchers Kara Hoover, a biological anthropologist at the University of Alaska in Fairbanks who now works at the National Science Foundation, and Claire de March, a biochemist at Université Paris-Saclay, reconstructed odor receptors from the genomes of three men from Neanderthal, a Denisovan, an ancient human and a database of modern human genomes. It was an attempt to recreate the noses of our closest ancient relatives.
“We need to really understand ourselves in our context,” rather than comparing humans to dogs or monkeys, as previous research on smell receptors has done, Hoover said. “When people look at humans, they see us as this bizarre outlier. But we really weren’t.”
Bringing ancient noses back to life in the laboratory
Hoover compared the genomes of Neanderthals and Denisovans to those of humans, targeting 30 olfactory receptors, genes that allow us to perceive smells. She identified 11 receptors that contained unique DNA variations in extinct species, variations that have not appeared in humans.
Then de March built those unique receptors in the lab, mutating human receptors to match the amino acid sequence of the extinct Neanderthal or Denisovan.
He then exposed the extinct receptors to hundreds of odors and measured their responses based on how quickly and how intensely they lit up with activity.
The sample size in this study was small, as only a few Neanderthal and Denisovan individuals have been genetically mapped. Graham Hughes of University College Dublin, who studies sensory perception in mammalian genomes and is unaffiliated with the study, also noted that DNA degrades over time, which can affect the results of any assessment of ancient genomes.
However, “the fact that we can now examine the genomes of ancient species and determine their possible sensory spaces and dietary specialties is very exciting for the field of sensory perception,” Hughes told Insider in an email.
To Hoover’s surprise, Neanderthals, Denisovans, and humans all seemed to have the same repertoire of smells.
It wasn’t that our extinct relatives could smell scents undetectable by humans, or vice versa. Instead, Denisovan was found to have more sensitive noses than humans, while Neanderthals appeared to have weaker noses, especially, in a group, to stinky body odors.
A lucky mutation for cave-bound Neanderthals
One of the Neanderthals had a genetic mutation that decreased his ability to smell androstadienone, a chemical associated with the smells of urine and sweat. This could have been of great help to those living in close proximity to other Neanderthals in caves.
“It’s kind of funny that of all the things they would stop smelling, that would be it,” Hoover said.
The Neanderthal used in the study represents an entire population of the species that lived at high altitudes in Siberia. The other Neanderthal samples, from different parts of the world, did not have that mutation.
Only two smell-related genes from the Neanderthal genome were different from those of humans.
A Denisovan by any other name would smell what is “sweet”
The Denisovan’s propensity for sniffing out sweet scents may have helped them find high-calorie, sugary foods like honey. Its receptors also responded with increased sensitivity to spicy smells, such as cloves or herbs.
Hoover described this as one of the earliest biological insights we have about Denisovans.
It is difficult to go from genetic information to the activity of odor receptors and thus to an individual’s subjective sensory experience, much less how they might behave in response.
“Each person might perceive things a little differently, and we can never say that what we consider to smell ‘sweet’ is the same as what another species would consider to smell ‘sweet,'” Graham said.
However, the study opens a bridge from DNA to the real-world experience of our extinct relatives. Other similar searches, with more samples of ancient genomes, could reveal a clearer picture of Neanderthal and Denisovan life.
“Ultimately, what our work has shown us is that we are more alike than we are different” when it comes to smell, Hoover said.
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