The urge to predetermine the sex of a baby is as old as our species. After Eve gave birth to Cain and Abel, she and Adam probably tried for a girl. But ask any expectant parents which sex they're hoping for, and you'll hear something like, "We don't care, as long as the baby's healthy." No doubt, this is the truth  -- but maybe not the whole truth.

In many countries, gender bias has long been embedded in cultural tradition, with society placing a higher value on male children. Boys carried on the family name; the eldest son inherited the family's wealth; males did the hard labor in factories and fields to bring in money; and male children married without having to supply a dowry. In modern-day America, however, these reasons rarely hold water.

So why the interest in choosing a future Dick or Jane? The answers vary. Some couples want to avoid passing on a hereditary disease that almost exclusively affects boys, such as hemophilia or Duchenne's muscular dystrophy. Others want to "balance" their family  -- they have two boys and dream of a girl, or want to give their two daughters a little brother. Regardless of the reasons, more and more prospective parents are expecting science to give them the power to choose the sex of their babies. And not surprisingly, given the rules of supply and demand, a number of laboratories have responded with a spate of sex-selection methods.