Today's physicians may have all the tools modern science can offer -- but they still look to an ethical guidepost that's more than two thousand years old. "First, do no harm" -- a simple, but profound mandate gleaned from the wisdom of Hippocrates. The words remain relevant -- yet modern doctors face ethical dilemmas Hippocrates never could have foreseen.

For example, science now enables couples to "engineer" the sex of their future children. But should they interfere with a matter once left to fate simply because medical technology empowers them to "order" a boy or a girl as they might select the fabric of a new couch? Medical advances such as this are coming almost faster than our ability to fully comprehend the ethical consequences.

Take the science of genetic mapping -- it can alert us to an impending illness ticking inside our body like a time bomb. But health insurers could one day use that same technology as a way of screening policyholders and denying coverage to persons destined to become ill.

Plus, there's the question of who should benefit from all that modern medicine has to offer. In recent months, a twice-convicted California felon received a heart transplant while in prison. Should a person who's acted as a predator be given the gift of life -- and at taxpayers' expense?

In the 21st century, medicine and ethics are still as interwined as ever. But it's no longer a simple matter of abiding by the ancient code of doing no harm. Today, it's a question of deciding whether to perform yet another medical miracle just because technology has made miracles an everyday possibility.