Only a tiny genetic difference can separate a macho man from a wimp, says a study published today. A variation in a single gene may explain why some people can withstand pain - or other physical or emotional stress - better than others, a team from the University of Michigan and the National Institutes of Health reports. In the journal Science, the team describes how a small variation in the gene encoding an enzyme - catechol-O-methyl transferase, or COMT - made a significant difference in the pain tolerance, and pain-related emotions and feelings, of volunteers. Genetics may not make all...