Saturday, April 2, 2011

Are You Tasteblind?

Imagine being handed a small cup of liquid to taste, and as the liquid sweeps over your tongue, you taste nothing special—it’s just sugar water, you think. Meanwhile, the person next to you has downed an identical cup of liquid, only to spit it out in disgust. Now imagine the same scenario, but you and the person beside you are chimpanzees instead.

An experiment was conducted in the late 1930s on chimpanzees to see whether they could detect the presence of a certain bitter compound called phenylthiocarbamide, or PTC for short. For the experiment, twenty-seven chimpanzees were given solutions of sugar and PTC. Twenty of them reacted to the solutions rather negatively. (Some of those twenty even behaved hostilely to the experimenters in an attempt to express their distaste with the drink they were given.) Those twenty were labeled as tasters because they could taste (and hated) the bitter PTC. The remaining seven drank the solutions without fuss, apparently not tasting any bitterness, and were labeled as nontasters.

The origins of this experiment were quite human and emerged into our scholarly knowledge through a puff of smoke—or rather, through a puff of powder. In 1931, A chemist by the name of Arthur L. Fox was preparing powdered PTC when a cloud of it flew into the air. To Fox’s surprise, a nearby co-worker complained that the dust cloud tasted bitter in his mouth. Fox, who got a much more intense hit of the dust, tasted nothing. Even after tasting the powder directly, he still couldn’t discern any bitterness.

This powder cloud accident with PTC, which could be the chagrin of any laboratory (for sending powdered chemicals into the air is rarely a good thing in terms of safety), instead launched Fox into an interesting discovery in science.

The bitterness of PTC, as it turns out, can only be detected by certain members of the human population (and the same deal for chimps and other primates, for that matter). After the incident in the lab, Fox went on to test this peculiarity in PTC tasting on more people and found a clear divide between the people who could taste and the people who could not taste PTC. Current studies seem to indicate that about 70% of humans are tasters, while the rest are nontasters.

Much like being colorblind, being “tasteblind” to PTC has been linked to mom and dad—or in other words, genetics. PTC has played a powerful role in genetics since its discovery. Since it’s easy to test for the ability to taste PTC (simply give the subjects some PTC to dab against their tongues), PTC has been used in many genetics experiments to investigate topics like inheritance as well as evolution. However, given that PTC does not actually occur naturally in food, why did we evolve to have a seemingly useless gene that determines our ability taste the bitterness of PTC?

Studies have looked into this question of evolution, which led to studies such as the ones conducted on the chimps, human’s closest living evolutionary relative. The particular chimp experiment described earlier was unfortunately cut short due to World War II, but lasted long enough to link genes to a chimp’s ability to taste PTC. Moreover, the experimenters noticed the genetic distribution of nontasters and tasters in chimps look suspiciously similar to that of humans, suggesting that humans and chimps received their ability to taste PTC from some common ancestor.

Even eighty years after Fox’s 1931 discovery, scientists are still investigating why evolution gave some of us the power to taste PTC. The most common hypothesis is that it is linked to food preferences in some way that is evolutionary favorable. Perhaps unlocking the secrets behind PTC will help us understand why tastes in food are so varied. However, there are no definitive experimental results proving this… yet. Studies have also suggested further interesting implications of PTC, such as how people who can taste PTC may have lower body mass index and are less likely to be addicted to nicotine.

Now the question is—can you taste PTC? You can find out if you’re a taster or a nontaster as well as learn more about PTC and genetics during the Festival’s Science Carnival. Look for the Science of Taste & Paint booth during 12-4pm on Saturday, May 7 at the Cambridge Public Library!

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