Before they are born, all human beings—including yourself—spend
nine months in their mothers' wombs. At the beginning of its
development, each human being consists of a tiny collection of
cells just starting to divide and develop. On the 22nd day, the
embryo is even smaller than a baked bean. One day, a small node
of cells in the center of that assemblage receives a command and
suddenly starts pulsating. All the other cells in the body lie
quiet. But this group is in constant motion, and never stops for
as long as the person will live. Never does it feel the need to
stop for even a moment's rest—not until the day, decades later,
when it receives the ultimate command to stop. During the
intervening period, a human being completes his or her lifespan.
Who gives this tiny node the command to start and finally stop?
This perfect pump, which began its beating when you were just
three weeks old in your mother's womb, bears a most important
responsibility: ensuring the circulation of the blood in your
body. In other