The yeast that causes thrush--an infection of the mouth and tongue--can reproduce homosexually, offering a clue as to why the yeast-caused infection can be so difficult to treat. When mating, the yeast known as Candida albicans can take one of two sexes: a or alpha. When researchers mixed the two types of yeast, they found that yeast cells of the same sex mated, although not very often, according to the study published in Nature. And