Is Bitter Better?

Foxgloves growing “outside the fence” near Cygnet, Tasmania.

Is Bitter Better?

John Reid

According to a recent article in Science magazine (“How modern humans ate their way to world dominance” by Ann Gibbons) humans have fewer bitter-taste genes than chimps. She writes:

… anthropological geneticist George Perry of Pennsylvania State University, University Park, and his colleagues compared the genomes of modern humans and chimpanzees to the newly published genomes of a Neandertal and one of its close relatives, a mysterious human ancestor known as a Denisovan, known only from a few bones found in a Russian cave. All three groups of humans had lost two bitter taste genes, TAS2R62 and TAS2R64, that are still present in chimpanzees, the team reports this month in the Journal of Human Evolution.

Two million years ago, our early ancestors such as Australopithecus or early members of Homo likely found wild yams and other tubers bitter. But as humans began to cook, they could roast tuberous root vegetables long enough that they weren’t as bitter. (Today, hunter-gatherers still rely on roasted tubers as a major source of calories.) At the same time, hominins—members of the human family—lost those two particular bitter taste genes, so they were presumably able to eat a wider range of tuberous plants. Modern humans, Neandertals, and Denisovans all lost the ability to detect the bitter flavor in some wild plants and eventually modern humans bred varieties of squashes, gourds, and yams that are less bitter than the wild types.

My wife and I have been gardening on the edge of native forest in Southern Tasmania for a decade now and we have had some hands-on experience with native animals and bitter plants.

Rufous wallabies (Thylogale billardierii) are particularly voracious and will even eat potato tops. “Will it grow outside the fence?” is a popular topic among local gardeners. Bulbs such as daffodils will survive and sometimes beds of daffodils can be seen in wild places decades after house and gardener have disappeared.

We have noticed that plants noted for their alkaloid content, particularly foxgloves (digitalis) and tobacco (nicotiana), do quite well outside the fence, presumably because they taste bitter to the animals.

Now here’s the thing: presumably these plants evolved to secrete poisonous alkaloids to protect themselves from being eaten by animals and the taste genes of the animals co-evolved to prevent them from being poisoned by alkaloids. Hence having fewer bitter taste genes should be an evolutionary disadvantage rather than an advantage as the article suggests.

Maybe we humans lost the TAS2R62 and TAS2R64 genes because, having learned how to cook, we no longer needed them.