You may be able to blame some of your unhealthy habits on our genes. Everyone has one of two genes that cause them to either taste, or not taste, a certain bitter substance. The ability to taste these substances developed long ago, to protect people living in places where bitter tastes were a way to identify poisons. Today, the ability to taste?or not taste?that compound influences what people eat and even whether they become smokers.

Scientists can tell which gene you have by testing to see if you can taste Phenylthiocarbamide (PTC), which isn’t found in nature, but tastes a lot like those poisons. Geneticist Stephen Wooding says, "We found evidence at the molecular level that natural selection has maintained the variation in the gene that allows us to taste or not taste PTC." This was discovered in 1930, when chemist Arthur Fox accidentally spilled PTC in a laboratory and noticed that some people could taste it, while others could not.

People who can taste PTC are less likely to eat vegetables like broccoli, which is bad, but it may also prevent them from liking the acrid smoke of cigarettes, which is good. Wooding says, "Among smokers, there seems to be an excess of PTC non-tasters, so it seems that PTC tasters are less likely to smoke."

The worldwide the ratio stays at about 75/25 between PTC tasters and non-tasters. One of these two genes is active in everyone, no matter where you live in the world. But everyone carries two of these genes, even though one is recessive, meaning you could have two copies of the taster gene, one taster and one non-taster, or two non-tasters. "We hypothesize that people carrying one copy of each allele are able to taste a broader range of toxic, bitter compounds, and have an evolutionary advantage," Wooding says. Now that we no longer forage for plants in the wild, these genes could be what turn people fussy eaters or smokers.

We can learn everything we need to know about other people by reading their auras.

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