A taste for sweet – an anthropologist explains the evolutionary origins of why you’re programmed to love sugar

The sweetness of sugar is one of life’s greatest pleasures. People’s love for sweets runs deep, and food companies lure consumers into their products by adding sugar to almost everything they make: yogurt, ketchup, fruit snacks, breakfast cereals, and even supposedly healthy foods like granola bars.

Elva Etienne / Moment via Getty Images – The Conversation

Schoolchildren learn as early as kindergarten that sweet candy belongs to the smallest end of the food pyramid, and adults learn from the media about the role of sugar in unwanted weight gain. It is hard to imagine a greater disconnect between strong attraction to something and rational disdain for it. How did people end up in this predicament?

I am an anthropologist who studies the evolution of taste perception. I think an insight into the evolutionary history of our species can provide important clues about why it’s so hard to say no to candy.

sweet taste detection

The main challenge our ancient ancestors faced was getting enough food.

The basic activities of daily life, such as raising young, finding shelter and securing enough food, all require energy in the form of calories. Individuals who are more efficient at gaining calories tend to be more successful at all of these tasks. They lived longer and had more children alive — and had greater fitness in an evolutionary sense.

One factor that contributed to the success was how adept they were at foraging. Being able to detect sweet things – sugars – can give a person a great deal of attention.

In nature, sweetness indicates the presence of sugars, which is an excellent source of calories. So foragers able to perceive sweetness can discover if and how much sugar is present in potential foods, especially plants.

This ability allowed them to quickly assess the calorie content of a taste before putting much effort into collecting, processing, and eating the items. The discovery of sweetness helped early humans gain more calories with less effort. Instead of random browsing, they can target their efforts, improving their evolutionary success.

sweet taste genes

Evidence for the vital importance of sugar discovery can be found at the most basic level in biology, the gene. Your ability to perceive sweetness is not accidental; It is etched into the genetic blueprints of your body. Here’s how this meaning works.

Microscopic view of cells just below the surface of the tongue.
Microscopic cross-section of the surface of the tongue. Taste buds are clusters of cells embedded under the surface of the tongue, facing the mouth through a small hole (top). Here, the taste bud is the circular mass of cells in the center.
Ed Rechke/Stone via Getty Images

Pleasant perception begins in the taste buds, which are clusters of cells just below the surface of the tongue. They are exposed to the inside of the mouth through small openings called taste pores.

Each different subtype of cells within the taste buds responds to a specific taste quality: sour, salty, salty, bitter, or sweet. The subtypes produce receptor proteins corresponding to their taste qualities, which sense the chemical composition of foods as they pass through the mouth.

One of the subtypes produces bitter receptor proteins, which respond to toxic substances. Another product that produces delicious receptor proteins (also called umami), which sense amino acids, the building blocks of proteins. Cells that detect sweets produce a receptor protein called TAS1R2/3, which detects sugars. When that happens, it sends a nerve signal to the brain for processing. This message is how you see the sweetness of the food you ate.

Genes encode instructions for how to make each protein in the body. The sugar-detection receptor protein TAS1R2/3 is encoded by a pair of genes on chromosome 1 of the human genome, aptly named TAS1R2 and TAS1R3.

A black bat hanging upside down from a branch holding a fruit
Fruit bat has a sweet flavour.
Avalon/Universal Images Collection via Getty Images

Comparisons with other species reveal how deep the beautiful perception is in humans. The TAS1R2 and TAS1R3 genes are not only found in humans – most other vertebrates also have them. They are found in monkeys, cattle, rodents, dogs, bats, lizards, pandas, fish, and countless other animals. The two genes have been in place for hundreds of millions of years of evolution, ready for the first human race to inherit.

Geneticists have long known that genes with important functions remain intact by natural selection, while genes that have no vital function tend to decay and sometimes disappear altogether as species evolve. Scientists think of this as a use-or-loss theory of evolutionary inheritance. The presence of the TAS1R1 and TAS2R2 genes across many species attests to the advantages that sweet taste has offered over eons.

The use-or-loss theory also explains the fascinating discovery that animal species that do not encounter sugars in their typical diets have lost their ability to perceive it. For example, many carnivores, who benefit little from the perception of sugars, harbor only a degraded residue of TAS1R2.

liking sweet

The body’s sensory systems detect myriad aspects of the environment, from light to heat to smell, but we’re not all drawn to them the way we’re attracted to sweetness.

A good example of this is another taste, bitterness. Unlike sweet receptors, which detect desirable substances in foods, bitter receptors detect undesirable substances: toxins. And the brain responds appropriately. While the sweet taste tells you to keep eating, the bitter taste tells you to spit out things. This has an evolutionary meaning.

So while your tongue detects tastes, your brain decides how to respond. If responses to a particular sensation are consistently beneficial across generations, natural selection locks them in place and they become instincts.

Even newborns prefer sweet and aversion to bitter.

It is the case with the bitter taste. Newborns do not need to be taught to hate the gallbladder – they instinctively reject it. The opposite is true for sugars. Experiment after experience finds the same thing: people are drawn to sugar from the moment they are born. These responses can be shaped by subsequent learning, but they remain at the heart of human behaviour.

Sweetness in the future of mankind

Anyone who decides they want to reduce sugar consumption faces millions of years of evolutionary pressure to find and consume it. People in the developed world now live in an environment in which society produces more sweet and refined sugars than they can eat. There is a devastating mismatch between the evolving drive to consume sugar, the current access to it and the human body’s responses to it. In a way, we are the victims of our own success.

The attraction to sweetness is so relentless that it’s called an addiction similar to nicotine dependence — one that is itself hard to beat.

I think it’s even worse. From a physiological point of view, nicotine is an undesirable foreigner to our bodies. People like it because it plays tricks on the brain. By contrast, the craving for sugar has been around and genetically encoded for eons since it provided basic fitness benefits, the ultimate evolutionary currency.

Sugar doesn’t fool you. You respond precisely as programmed by natural selection.

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This article is republished from The Conversation, a non-profit news site dedicated to exchanging ideas from academic experts. Written by: Stephen Wooding, University of California, Merced.

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Stephen Wooding does not work, consult, hold stock, or receive funding from any company or organization that may benefit from this article, and has not disclosed any relevant affiliations following their academic appointment.

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