Creationism in Crisis - Scientists Have Discovered How Our Sense of Smell Has Evolved

Creationism in Crisis

Scientists Have Discovered How Our Sense of Smell Has Evolved

Neanderthal hunter.
How good was their sense of smell?

Reconstruction of a Neanderthal woman.

Bacon Cph, CC BY 2.5, via Wikimedia Commons

Study offers new insight on what ancient noses smelled | UAF news and information.

Inadvertently exposing laughable Creationists claims that the Theory of Evolution is a theory in crisis about to be overthrown in the scientific consensus by Creationist superstition, including magic done by unproven supernatural entities, a study led by University of Alaska Fairbanks biological anthropologist Kara C. Hoover and Universite Paris-Saclay biochemist Claire de March, shows how our sense of smell evolved as an adaption to new environments, in classic example of evolution by natural selection.

The research involved a comparative genetic analysis of the genomes of modern humans, Neanderthals and Denisovans.

The research is explained in a University of Alaska Fairbanks (UAF) news release:

It sounds a little like Stone Age standup: A Denisovan and a human walk past a bees’ nest heavy with honeycomb. What happens next? According to a study led by University of Alaska Fairbanks biological anthropologist Kara C. Hoover and Universite Paris-Saclay biochemist Claire de March, the Denisovan, with the species’ greater sensitivity to sweet smells, may have immediately homed in on the scent and beat the human to a high-energy meal.

This research has allowed us to draw some larger conclusions about the sense of smell in our closest genetic relatives and understand the role that smell played in adapting to new environments and foods during our migrations out of Africa.

[Smell is integral to the human story.] Such a strongly overlapping olfactory repertoire suggests that our generalist approach to smelling has enabled us to find new foods when migrating to new places — not just us but our cousins who left Africa much earlier than us!

Profesor Kara C. Hoover
Department of Anthropology
University of Alaska Fairbanks, Alaska, USA

A paper on the research, recently published in iScience, was written by collaborators from UAF, Duke University, Universite Paris-Saclay, Tokyo University of Agriculture and Technology, and the University of Manchester. The study investigated whether humans share a sense of smell with their now-extinct Denisovan and Neanderthal cousins, who left Africa about 750,000 years ago. Contemporary humans left Africa about 65,000 years ago.

To recreate the noses of our extinct genetic relatives and compare them to those of present-day people, the research team used publicly available genome sequences from multiple Neanderthals, one Denisovan and one ancient human. They used data from the 1000 Genomes project to represent modern humans.

They then compared 30 olfactory receptor genes from each group. The team found that 11 of the receptors had some novel mutations present only in extinct lineages. In the largest study of its kind to date, the team created laboratory versions of those 11 olfactory receptors and then exposed them to hundreds of odors at different concentrations.

When the receptors detected an odor, they literally lit up. The speed and brightness of the luminescence told the scientists whether, how soon and to what degree each “nose” could smell the odors. While the receptors could detect the same things as modern humans, they differed in sensitivity to many of the odors.

We literally reproduced an event that hadn’t happened since the extinction of Denisova and Neanderthal 30,000 years ago: an extinct odorant receptor responding to an odor in cells on a lab bench. This took us closer to understanding how Neanderthal and Denisova perceived and interacted with their olfactory environment.

Claire A. de March, lead author
Institut de Chimie des Substances Naturelles
Université Paris-Saclay, Gif-sur-Yvette, France And Department of Molecular Genetics and Microbiology
Duke University Medical Center, Durham, NC, USA

This is the most exciting research I have ever been involved in. It shows how we can use genetics to peer back into the sensory world of our long-lost relatives, giving us insight into how they will have perceived their environment and, perhaps, how they were able to survive.

Matthew Cobb, co-author
Faculty of Life Sciences
The University of Manchester, Manchester, UK

Neanderthals, who lived in Eurasia between 430,000 and 40,000 years ago, had the poorest sense of smell. For example, the Neanderthal from the Chagyrskaya Cave couldn’t detect the sex steroid androstadienone, which smells something like sweat and urine. That may have been useful, Hoover said, given that they were trapped in close quarters in caves during glacial maximums, when the ice sheets from the poles expanded southward and made many areas uninhabitable.

Each species must evolve olfactory receptors to maximize their fitness for finding foodX. In humans, it's more complicated because we eat a lot of things. We're not really specialized.

Professor Hiroaki Matsunami, co-author
Department of Molecular Genetics and Microbiology
Duke University Medical Center, Durham, USA

Denisovans have left behind less physical evidence than Neanderthals. They are known mostly from modern-day Siberia, where remains in the Denisova Cave were dated to between 76,200 and 51,600 years ago. Denisovans were generally more sensitive to odors than humans and much more sensitive than Neanderthals. They were most responsive to sweet and spicy smells like honey, vanilla, cloves and herbs. That trait could have helped them find high-calorie food.

Present-day humans fell somewhere in the middle.

In many species, olfactory receptors have been linked to their ecological and dietary needs.

The same research is also the subject of a press release from Duke University, the university to which several of the team, are affiliated and where the lead author, Claire A. de March, completed her PhD:

If you had the grooming habits of a Neanderthal, perhaps it’s a good thing your nose wasn’t as sensitive to urine and sweat as a modern human’s.

And if you lived the hunting and gathering lifestyle of a Denisovan on the Asian steppes, your strong nose for energy-rich honey was almost certainly an advantage.

Though we can’t really know what these two extinct human species perceived or preferred to eat, a new study from Duke University scientists has figured out a bit more about what they might have been able to smell.

Using a technique they developed that allows researchers to test smell sensitivity on odor receptors grown in a lab dish, researchers Claire de March of CNRS Paris Saclay University and Hiroaki Matsunami of Duke University were able to compare the scents-abilities of three kinds of humans. Their work appeared Dec. 28 in the open access journal iScience.

Drawing from published databases of genomes, including ancient DNA collections amassed by 2022 Nobel Prize winner Svante Pääbo, the researchers were able to characterize the receptors of each of the three human species by looking at the relevant genes.

It is very difficult to predict a behavior just from the genomic sequence. We had the odorant receptor genomes from Neanderthal and Denisovan individuals and we could compare them with today’s humans and determine if they resulted in a different protein.

The Neanderthal odorant receptors are mostly the same as contemporary humans, and the few that were different were no more responsive/

Claire A. de March

So then they tested the responses of 30 lab-grown olfactory receptors from each hominin against a battery of smells to measure how sensitive each kind of receptor was to a particular fragrance.

The laboratory tests showed the modern and ancient human receptors were essentially detecting the same odors, but their sensitivities differed.

We don’t know what Denisovans ate, but there some reasons why this receptor has to be sensitive

[Neanderthals] may exhibit different sensitivity, but the selectivity remains the same.

Each species must evolve olfactory receptors to maximize their fitness for finding food. In humans, it’s more complicated because we eat a lot of things. We’re not really specialized.

Some people can smell certain chemicals, but others can’t. That can be explained by functional changes.

Professor Hiroaki Matsunami

The Denisovans, who lived 30,000 to 50,000 years ago, were shown to be less sensitive to the odors that present-day humans perceive as floral, but four times better at sensing sulfur and three times better at balsamic. And they were very attuned to honey.

Contemporary hunter-gatherers such as the Hadza of Tanzania are famous for their love of honey, an essential high-calorie fuel.

Neanderthals, who were still around up to 40,000 years ago and who apparently swapped a few genes with modern humans, were three times less responsive to green, floral and spicy scents, using pretty much the same receptors we have today.

Odor receptors have been linked to ecological and dietary needs in many species and presumably evolve as a species changes ranges and diets.

The team's findings were published open access last December in the journal iScience:

Graphical abstract

Highlights

• Neanderthal and Denisovan ORs vary less than human ORs but our repertoires are similar
• OR variation may have helped humans adapt to new environments
• There are limited functional differences in odor specificity across lineages
• Neanderthals are less sensitive to odors than humans, and Denisovans more sensitive

Summary

Humans, Neanderthals, and Denisovans independently adapted to a wide range of geographic environments and their associated food odors. Using ancient DNA sequences, we explored the in vitro function of thirty odorant receptor genes in the genus Homo. Our extinct relatives had highly conserved olfactory receptor sequence, but humans did not. Variations in odorant receptor protein sequence and structure may have produced variation in odor detection and perception. Variants led to minimal changes in specificity but had more influence on functional sensitivity. The few Neanderthal variants disturbed function, whereas Denisovan variants increased sensitivity to sweet and sulfur odors. Geographic adaptations may have produced greater functional variation in our lineage, increasing our olfactory repertoire and expanding our adaptive capacity. Our survey of olfactory genes and odorant receptors suggests that our genus has a shared repertoire with possible local ecological adaptations.

de March, Claire A.; Matsunami, Hiroaki; Abe, Masashi; Cobb, Matthew; Hoover, Kara C.
Genetic and functional odorant receptor variation in the Homo lineage
iScience 26(i); 2022. doi: 10.1016/j.isci.2022.105908

Copyright: © 2022 The authors.
Published by Elsevier Open access.
Reprinted under a Creative Commons Attribution – NonCommercial – NoDerivs license CC BY-NC-ND 4.0)

The researchers are in no doubt whatsoever, that natural selection drove these differences in the olfactory sensitivity of these three closely rated hominins, as each adapted to their particular environment, cultural preferences for particular food and social habits. Nowhere have they had to invoke magic or supernatural deities in their explanation for the observable evidence.

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