About a million years ago, one tiny change in DNA gave our ancestors the ability to perceive a bitter compound common in olives, nuts and seeds, scientists reported recently in the journal Molecular Biology Evolution.
That means the bitter-tasting mutation was present long before modern humans existed. And it stuck around as we evolved in Africa about 200,000 years ago.
But here's the twist: The mutation probably didn't arise — and persist — for the reason that most of us think.
"People in the past have thought that bitter taste perception may have evolved for avoiding toxic substances," says biologist Sarah Tishkoff of the University of Pennsylvania, who led the study. "If you're a hunter-gatherer, you don't want to eat a poisonous plant. A bitter taste tells [you] immediately to avoid it."
But that's not what she and her postdoc Michael Campbell found when they analyzed taste genes across indigenous populations in Africa.
Campbell and her team tracked down 74 ethnic groups that still practice ancient methods of subsistence, such as hunter-gatherers and nomadic herders.
The team measured how easily people in each group could taste two bitter compounds, including the chemical in aspirin. They also sequenced two genes involved in detecting bitter flavors on the tongue.
"We had to haul huge numbers of bottles and chemicals to remote areas all across Africa," Tishkoff tells The Salt. "This was a ton of work."
She thought that hunter-gatherers would be more likely to carry the mutation that boosts their sensitivity to the aspirin compound because they and their ancestors foraged for food.
"We thought we'd see a difference in the bitter genes between the hunter-gatherers and pastoralists because of their diet," Tishkoff says. "But there was no correlation all."
In fact, while the ability to perceive bitter flavors is ubiquitous in people outside of Africa, that was not the case inside the continent, she says. In Africa, she found that people's ability to detect bitter tastes varied by geography — but it had nothing to do with what they ate or how they got their food.
So if bitter sensing didn't help our ancestors avoid poisonous plants, why have the genes stuck around for so long?
No one is really sure yet, Tishkoff says.
"These genes could be detecting a compound we don't know anything about," she says. Or they could be performing a task that's completely unrelated to taste all together.
In the past few years, scientists have started to realize that bitter taste receptors are all over the body, Tishkoff says. These receptors have turned up in cells in the gut, lungs and even the testes.
"So the receptors are not only altering how we perceive food," she says, "but probably also our physiology, in ways we have no idea about."