Is the human sense of smell disappearing?

There are millions of olfactory neurons in our noses, each with a class of receptors that recognize odors.

When we smell a smell, we actually inhale volatile molecules that bind to specific receptors.

As a result, we only need about 400 different types of receptors to recognize a variety of odors.

However, people have different olfactory receptors.

A 2013 study published in Nature Neuroscience found that, on average, more than 30% of olfactory receptors differ between any two people.

This may also explain why some people think the smell is unbearable, while others think it's nothing and can even take a deep breath.

Old and young olfactory receptors.

By comparison, the team targeted two new olfactory receptors, corresponding to Jiale Musk and 3M2H.

Unsurprisingly, there are a large number of mutations in the genes that encode these receptors, which affects how people feel about the corresponding odors.

The researchers further compared the genetic mutations of the two newly discovered receptors, while also combining 27 other known olfactory receptor-related mutations.

In this way, they can understand whether these mutations enhance or weaken our sense of smell before and after the time these mutations appear on the human genome during evolution.

"although this study is not intended to demonstrate or deny this hypothesis, we also need to consider whether there is a sample selection bias.

However, based on the current data, this study does support the hypothesis that the olfactory gene pool in primates deteriorates over time. "

Fewer genes, smaller olfactory bulbs.

The hypothesis of human olfactory degeneration is not recently put forward.

For a long time, there have been some theories that as vision becomes the dominant feeling, the sense of smell will become less and less important, so it is gradually being "abandoned".

In particular, scientists found that humans have about 1000 olfactory receptor-related genes, of which only 390 encode olfactory receptors, most of which are "pseudogenes" that do not work.

By contrast, mice have 1100 "working" genes and only 200 "pseudogenes".

In the 19th century, French neuroscientist Paul Broca (Paul Broca) put forward some "special" ideas about the human brain at the time.

For example, he points out that the frontal lobes of the human brain associated with language and thinking are larger than those of other animals.

By contrast, he noticed that our olfactory bulbs-a pair of structures used to sense odors-are smaller, flatter and less conspicuous.

Broca believes that these differences are significant.

He argues that the enlarged prefrontal lobe of human beings is the site of our free will, which makes human beings unique.

However, our olfactory bulb controls an animal sensation that forces us to engage in "basic behaviors" such as eating and sex.

Broca then more aggressively divided mammals into olfactory and non-olfactory animals, including humans, other primates and aquatic animals such as cetaceans.

Broca believes that humans are not unable to smell, but can consciously "shield" the effects of odors, which other mammals cannot do.

Humans are losing their sense of smell.

Huh?

To some extent, Broca's theory has become the cornerstone of olfactory research.

However, as the secret of the sense of smell has been revealed, the view that human beings are losing their sense of smell has caused a heated debate.

Similarly, some studies have shown that our sense of smell is not as bad as we think.

Even if there are fewer olfactory genes than other animals, humans are better than we expect, even more than other animals-depending on the smell.

John McGann of Rutgers University agrees that the number of olfactory-related genes does not tell the story.

Further studies have shown that some "pseudogenes" can actually be activated and play a role.

More importantly, olfactory receptors work together, so having 390 receptors doesn't mean you can only distinguish 390 odors.

"each species has its own strengths and weaknesses, and humans have a stronger sense of smell than other animals in some smells, such as the chemicals in our own blood and the taste of bananas.

We are much less sensitive to other odors, but that doesn't mean we have a worse sense of smell than mice. "

Similarly, some studies have pointed out that there are great differences in the sense of smell among different populations, and the deviation in sample selection may lead to misunderstanding.

Psychologist Asifa Majid of the University of Radbaud said: "typical olfactory studies focus on Western volunteers, but in their culture, the perception of smell is not particularly fine.

But people from other parts of the world, such as the Jahai in Malaysia and the Maniq in Thailand, are better at identifying and describing smells. "

According to Megan and neuroscientist Noam Sobel, humans may still have a strong sense of smell, but "most of us don't practice".

Megan tried to blindfold and find his way by smelling the ground; Sobel took a group of undergraduates to the park, blindfolded, and asked them to follow the smell of chocolate oil spilled on the floor for about 10 meters-they all succeeded.

When it comes to the blindfolded experiment of finding your way in the park by smell, although (no one will want to try), please don't imitate.