Dumplings must be dipped in vinegar! This was decided hundreds of millions of years ago!

While we savor the delicious flavors of modern food, we may not realize that for our ancestors, taste was a matter of life and death .

Animals have five main tastes: sour, sweet, bitter, salty, and umami. Before humans could print ingredient lists on food packaging, taste was responsible for analyzing food ingredients: sweet represents sugar and high calories, salty represents inorganic salts necessary for the human body, umami corresponds to nutrients related to protein, and bitter is a warning of potential toxicity.

Only the role of sour taste remains a mystery to scientists. We don’t know how it evolved, nor are we sure why it is preserved in the human body—it can’t be for eating dumplings with vinegar.

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01

The special feature of sour taste

The sour taste is special in that the perception process is different from other tastes.

There are many taste buds on our tongue, and each taste bud contains more than a hundred taste cells. These cells sense the various flavors in food and transmit these signals to the taste cortex of the brain, so that we can taste the flavors.

The reason why taste cells can sense taste substances is thanks to the taste receptors on the cell membrane. When we taste food, we are actually sensing the chemicals in the food. When specific chemicals bind to specific taste receptors, taste signals are activated, telling the brain what it tastes like.

However, the mechanisms by which different tastes produce taste signals are different. Sweet, bitter and umami are produced by taste receptor proteins being activated, which then conduct signal transduction and trigger downstream cascade signal pathways. However, saltiness and sourness are different, as they are directly mediated by ion channels (the flow of ions in and out of the cell membrane).

Different seasonings. Copyright image, no permission to reprint

Researchers have discovered taste receptors for sweetness, bitterness, umami, and saltiness, but have yet to find the perception mechanism for sourness.

It wasn't until 2019 that two papers published in Cell and Current Biology finally pinpointed an ion channel in the tongue's sour taste receptors in mice - otopetrin-1 (OTOP1).

When we eat something acidic, the OTOP1 receptor allows hydrogen ions to cross the membrane and enter the taste receptor cell, thereby detecting the sour taste of the food.

However, even after understanding part of the perception mechanism of sour taste, it is still difficult for us to restore the evolution of sour taste. For other taste systems, by analyzing the genetic information corresponding to the taste receptor protein, we can understand the evolution of the corresponding taste based on gene mutations.

However, this method does not work for sour taste because the gene encoding OTOP1 is widely expressed. In addition to sensing sour taste, OTOP1 also plays a vital role in the inner ear, affecting the formation of otoliths . Some mutations in OTOP1 may not change sour taste, but may lead to certain vestibular diseases.

This makes it difficult to determine whether differences in OTOP1 are due to natural selection for sour taste, even if differences are found between species or populations.

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02

Origin of sour taste

However, this does not mean that the clues to the evolution of sour taste are lost.

In February 2022, ecologists from North Carolina State University in the United States and the authors conducted an extensive survey of the perception of sourness by different species, attempting to reconstruct the evolution of sour taste. The relevant research was published in the Proceedings of the Royal Society B.

After a long evolution, most animals today have lost (or have lost) some sense of taste. Dolphins seem to be able to taste only salty, and cats can't taste sweet. Therefore, researchers naturally thought that the sense of sour taste should be the same, and it has been lost many times in the long river of evolution.

However, the researchers tested about 60 species, from fish and amphibians to birds and mammals, and all of them showed the ability to sense sour taste. Among these animals, pigs and primates seem to have a special preference for sour foods, such as wild boars who particularly like fermented corn, and gorillas who have a special liking for sour fruits of certain ginger families.

Researchers can only speculate how the earliest vertebrates evolved a taste for sourness, but living fish offer clues.

Most of the taste buds of fish are not in their mouths, but on their faces, bodies, and beards. For aquatic organisms, the carbon dioxide dissolved in the water will affect the pH of the water, and these changes are very dangerous to fish. Therefore, being able to "taste" the acidity of the water with the surface of the body is very important for survival.

In fact, the researchers have found that genes related to the sour taste receptor OTOP1 are widespread in vertebrates and invertebrates, and therefore "almost certainly existed in the first vertebrate to have taste buds."

This suggests that the earliest vertebrates may have had the ability to detect acidic substances . In other words, the ability to sense sour taste is at least as old as vertebrates.

The ability of different species to perceive sour taste. Purple means they don't like sour taste, green means they like sour taste, and white means they are not sure about their preference for sour taste. Image source: original paper

03

Prefer sour taste

Humans and other species' preference for sour taste may also be a survival strategy.

Humans and many apes have lost the ability to synthesize vitamin C in their bodies, and sourness may serve as a reminder, like other tastes, of the ingredients in food—there may be a lot of vitamin C in it .

Another possible guess is that for many primates, rotting animals or plants are an important part of their diet. One way to judge whether these rotten foods are safe may be to see whether they are acidic - acidic means that the food is rich in lactic acid bacteria or acetic acid bacteria, and the acid they secrete will kill harmful bacteria.

Whatever the reason, once a taste for acidic foods emerged, especially when combined with a preference for umami, our ancestors may have begun experimenting with controlling decay to produce tastier results—what we now call fermentation.

Delicious pickled cucumbers. Copyrighted images from the gallery, no permission to reprint

Maybe next time you eat dumplings, you can experience more carefully the result of hundreds of millions of years of evolution of vertebrates given to humans - the sour taste.

"Hello, I made some vinegar today and I want to borrow some dumplings from you."

Reference Links:

[1]https://linkinghub.elsevier.com/retrieve/pii/S009286741930950X

[2]https://www.cell.com/current-biology/fulltext/S0960-9822(19)31161-3

[3]https://www.science.org/content/article/pucker-why-humans-evolved-taste-sour-foods

[4]https://royalsocietypublishing.org/doi/10.1098/rspb.2021.1918

Author: Global Science

Produced by: Science Popularization China-Starry Sky Project (Creation and Cultivation)

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