Different sensitivities to bitter tastes probably arose from evolutionary pressures in different parts of the world. Most toxic plants taste bitter, and nomadic groups that came into contact with a variety of plants would have, over time, developed a variety of receptors. People from malaria-infested parts of the world tend to carry a gene that makes them less sensitive to some bitter compounds, specifically those that contain cyanide. Researchers speculate that cyanide, ingested at low levels, fights malarial parasites while leaving the host unscathed. Juyun Lim, a sensory scientist in Oregon State University's Department of Food Science, says that we have a natural aversion to bitterness and certain odors: "Most people don't like beer the first time they try it."