Planet of the Apes: Why we hate broccoli

Biologists agree on the big picture when it comes to Darwinian evolution, but they're still working out many details. One longstanding puzzle is why there's so much variation from person to person, why some people like broccoli, for example, and others hate it.

There's evidence that people who hate broccoli are not being childish or stubborn. Some broccoli haters are reacting to compounds called glucosinolates, which are also present in brussels sprouts and other so-called cruciferous vegetables.

Some people taste these as intolerably bitter, and others can't taste them at all. The difference is genetic. The gene responsible, called hTAS2R38, comes in several forms, some of which enable people to detect this stuff.

The standard theory explaining this gene is that it helps us avoid harmful plant toxins.

But University of Pennsylvania geneticist Sarah Tishkoff didn't buy this. If it's so important, she asked, why would half of us be missing the ability to taste a whole class of dangerous plant-toxins?

To investigate, she teamed Penn geneticist Michael Campbell as well as researchers at Monell Chemical Senses Center, Rutgers, and National Institutes of Health, and went off to Africa, since it's the source of humanity and much of our variation.

Also on the team were researchers from French and African universities.

Luckily for the scientists, they didn't have to feed hundreds of subjects vegetables. People's reaction to natural glucosinolates can be tested by their reaction to a synthetic relative, called PTC. When they spike water with PTC, people taste either nothing or something nastily bitter.

Tishkoff said she thought they would find a simple evolutionary explanation - some people probably needed this particular toxin-detection system more than others depending on local food sources. "I thought this would be a way to see how people adapt to diverse diets."

What they found was a surprise, published in a recent paper in Molecular Biology and Evolution. The sensitivity to bitter taste varied far more than expected.

From Kenya to Tanzania to Cameroon, Tishkoff and Campbell studied how people differed in their taste perception and their DNA. They included 57 groups, including hunter-gatherers such as Pygmies, as well as a variety of farmers and herders.