Of all the superlatives connected with the London Olympics, none may be more remarkable than this: The games will feature the most extraordinary collection of physical specimens in the history of international sports.

Whether it's the chest-high legs that carry sprinter Usain Bolt down the track, or the raw power that 17-year-old swimmer Missy Franklin can generate from her 6-foot-1 frame and 76-inch wing span, the Olympic stars this summer have bodies custom-built for the sports they compete in. To borrow Lady Gaga's phrase, many of these medalists were simply "born this way."

"Nature, being born a certain way—it's a prerequisite for nurture," said Adrian Bejan, a professor of mechanical engineering at Duke University who has written extensively about evolution in sports.

These perfectly designed bodies now have an almost insurmountable advantage. Unless they are sick or injured or fall down, basic physics suggests they simply won't be beaten. This is partly a function of the information age. There are few secrets in sports anymore: A great athlete from nearly any country other than North Korea or Cuba can find the resources to excel. Long-distance runner Mo Farah was born in Somalia, trains in Oregon and runs for Great Britain. Athletes Performance, the Arizona-based training company, works with a Latvian long jumper, a Japanese hammer thrower, and athletes from 14 Chinese Olympic teams.

With high-level training so ubiquitous, God-given talent and physical advantages become the great differentiators. Consider Ms. Franklin, the precocious swimmer from Colorado who could win as many as seven medals in London, several of them gold, during the summer before her senior year in high school.