Women may not be known as the gender with the highest sex drive, but it turns out, at least in mice, males with an extra "girly" sex chromosome seemed to have an insatiable appetite for sex. In mammals, gender is determined by "sex chromosomes," the X and Y. If you have two X chromosomes, you are a female. If you have one X and one Y, you are a male. (Chromosomes are long strings of DNA that hold many genes; humans have 23 pairs of chromosomes, one set inherited from each parent.) The study was...