It isn't the most elegant of races. In a study that attempts to
elucidate one of the "central unsolved problems" in human
reproduction — what separates the tens of sperm cells that find
an egg, from the millions of cells ejaculated? — British
researchers are reporting that sperm crawl, collide and crash
head-on into the walls of the female reproductive tract in their
frantic swim to the site of fertilization. "Despite it being the
thing that put all of us here, effectively, we still know almost
nothing about how something so simple and key to life actually
happens in the body," said Dr. Jackson Kirkman-Brown, a senior
lecturer in reproductive sciences at the University of
Birmingham in the U.K. "Every time a woman gets or doesn't get
pregnant, there is something going on where what to me is an
incomprehensible number of sperm — two hundred million — get
reduced to a countable amount, 10, maybe." Popular wisdom holds
that sperm follow each other in their swim through the female
tract "rather like you or I migh