by As you walk through the woods and pass a beehive, you might catch the sweet scent of honey on the wind and suddenly be flooded with memories: having tea with Grandma or eating warm cookies 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, by the time you smelled the honey, your partner might already be climbing the tree looking for a sugary sweet.
That’s because Denisovans seem to have been especially sensitive to sweet smells like honey or vanilla, new research published in the journal iScience in January suggests. That 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 wide range of odors. The researchers think that helped humans adapt to new environments as they ranged across the globe, sniffing out new food 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 may not mean much. Understanding our earliest relatives, the other Homo species that migrated from Africa alongside us, may offer better context for our own sense of smell and give us insight into life in our early days.
Researchers Kara Hoover, a biological anthropologist at the University of Alaska at 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 Neanderthals. , one Denisovan, one ancient human, and one database of modern human genomes. It was an attempt to recreate the noses of our closest ancient relatives.
“We have to really understand ourselves within our own context,” rather than comparing humans to dogs or mice, as previous research on olfactory receptors has done, Hoover said. “When people look at humans, they see us as this weird outlier. But in fact, we weren’t.”
Bringing old noses to life in the lab
Hoover compared the genomes of Neanderthals and Denisovans with those of humans, targeting 30 olfactory receptors, genes that allow us to perceive odors. She identified 11 receptors that contained DNA variations unique to extinct species, variations that did not appear in humans.
De March then built these unique receptors in the lab, by mutating human receptors to match the amino acid sequence of extinct Neanderthals or Denisovans.
He then exposed the extinct receptors to hundreds of odors and measured their responses by how quickly and intensely they fired up with activity.
The sample size in this study was small, as only a few individual Neanderthals and Denisovans have been genetically mapped. Graham Hughes of University College Dublin, who studies sensory perception in mammalian genomes and is not affiliated with the study, also noted that DNA degrades over time, which can affect the results of any assessment of ancient genomes.
Still, “the fact that we can now look at the genomes of ancient species and determine their potential sensory gaps 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 seemed to have the same repertoire of scents.
It wasn’t that our extinct relatives could smell odors undetectable to humans, or vice versa. Instead, Denisovans turned out to have more sensitive noses than humans, while Neanderthals seemed to have weaker noses, especially, in a group, for stinky body odors.
A lucky mutation for cave-dwelling Neanderthals
One of the Neanderthals had a genetic mutation that decreased his ability to smell androstadienone, a chemical associated with the odors of urine and sweat. That could have been a big help to those who lived in close proximity to other Neanderthals in caves.
“It’s funny that of all the things that 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 in the Neanderthal genome were different from humans.
A Denisovan by any other name would smell what ‘sweet’ is
Denisovans’ propensity for sniffing out sweet odors may have helped them find sugary, high-calorie foods like honey. Its receptors also responded with increased sensitivity to spicy odors, such as cloves or herbs.
Hoover described this as one of the first biological insights we have about Denisovans.
It’s hard to get from genetic information to odor receptor activity and then to an individual’s subjective sensory experience, let alone how they would behave in response.
“Each person can perceive things slightly differently, and we can never say that what we consider to be a ‘sweet’ odor is the same as what another species would consider a ‘sweet’ odor,” Graham said.
Still, the study opens a bridge from DNA to the real-world experience of our extinct relatives. More research like this, with more samples from ancient genomes, could reveal a clearer picture of life for Neanderthals and Denisovans.
“Ultimately, what our work showed us is that we are more alike than different” when it comes to smell, Hoover said.
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