Scientists have done remarkably well in tracking down genes that are linked to diseases, identifying more than 100 illnesses that are associated with single-gene defects, such as Tay-Sachs, sickle-cell anemia and several forms of cancer. In dealing with behavior, however, the results have been more ambiguous. "The idea of finding a single gene that could orchestrate something as complex as behavior, while attractive, is probably not realistic," says Thompson, who notes that many factors tend to influence a persons actions. There is also an additional element: Studies exploring genetics and behavior are open to question on the methodologies they employ. "Looking for associations is complicated," says TIME science reporter Alice Park, "and there are many ways of looking at associations." Still, many scientists have come to the conclusion that there is a genetic link to homosexuality, but they concede this may not necessarily be true in all cases. And so for those looking to the certainty of science to orient their politics on gay issues, the only given from the latest ambiguity is this: more passionate debate from both sides.
The scientific debate over what causes homosexuality -- nature, nurture or a mixture of both -- just got even more complicated. Reflecting the complexity that is seeping into the field of genetics in general, a new study published in the journal Science failed to replicate the findings of widely publicized previous research that had linked homosexuality to a possible gene or set of genes. "Evidently, the idea of linking genes to behavior is not going to be as simple or easy as generally supposed," says TIME science correspondent Dick Thompson.