Evolution Up Against a Wall : FULL HOUSE: The Spread of Excellence From Plato to Darwin.<i> By Stephen Jay Gould (Harmony Books/Crown Publishing: $25, 256 pp.)</i>

For the past 15 summers, I have either competed in or directed “Race Across America,” a 3,000-mile, nonstop, transcontinental bicycle race. In the race’s first decade, the transcontinental record plummeted from 12 days and 3 hours to 7 days and 23 hours, but for the past five years it hasn’t budged even though half of the cyclists routinely break earlier records. Why?

Some of the race’s pioneers, not surprisingly, believe that they were simply better than today’s competitors; current riders blame weather conditions and other variables. Now I know that both sides are wrong, thanks to the work of Harvard paleontologist, evolutionary biologist and trendsetter Stephen Jay Gould, whose new book, “Full House: The Spread of Excellence From Plato to Darwin,” explains how the world develops over time, from the history of life to the history of sports.

Gould advances an interesting theory of biological life by applying it to one of his favorite interests, baseball. No one has batted .400 in baseball since Ted Williams in 1941 (for every 10 times at bat, he had four hits), and this unsolved mystery continues to stimulate books and brouhahas. The mystery is now solved, says Gould. It is not because players were better then (what he calls the Genesis Myth: “There were giants in the Earth in those days”) or because players today have tougher schedules, night games and cross-country travel (Rod Carew says night games are easier on the eyes and travel by jet beats a train any day). It is because the overall level of play among all players has marched ever upward toward a hypothetical outer wall of human perfection.

Paradoxically, .400 hitting has disappeared because today’s players are better, not worse. The majority are better, making baseball’s creme de la creme stand out from mediocre players far less than in the past. Today’s best ballplayers may be absolutely better--improved training, equipment, diet--than players 50 years ago, but every position in the field now is manned by players who are also so much better than before.

OK, so what? For Gould, the disappearance of .400 hitting is just one of many examples of how various systems change over time and how our biased notion of progress has led us to misunderstand historical change. “All of these mistaken beliefs arise out of the same analytical flaw in our reasoning--our Platonic tendency to reduce a broad spectrum to a single, pinpointed essence. This way of thinking allows us to confirm our most ingrained biases--that humans are the supreme being on this planet; that all things are inherently driven to become more complex . . . , “ he argues.

Evolution can be illustrated similarly by a range of organisms spanning from simple cells to complex mammals. In the spread of life, there is a “left wall” of simplicity: anything simpler would not be alive. What else could evolution have done, Gould asks? For life to evolve, it had to get more complex. Evolution reflects “an increase in total variation by expansion away from a lower limit, or left wall, of simplest conceivable form.” The same thing goes for size: “Size increase is really random evolution away from small size, not directed evolution toward large size.”

Why is this idea revolutionary? Because, Gould says, change is a result of the whole system (the “full house”) expanding, not because life is progressing toward a fixed goal. As Gould has written before, evolution is not “going” anywhere. It is massively quirky and accidental, and we are but a minor twig on the richly branching bush of life. “The vaunted progress of life is really random motion away from simple beginnings, not directed impetus toward inherently advantageous complexity.”

Applying the model to science and the creative arts, Gould wonders why, in a gene pool significantly larger than in the 17th century and with endlessly greater opportunities for children to become artists, we don’t see the likes of Bach, Handel, Haydn, Mozart and Beethoven. Gould cautiously suggests that “perhaps the range of accessible styles can become exhausted, given the workings of human neurology and the consequent limits of understanding. Perhaps we can reach a right wall of potential popularity, where our continued adherence to an ethic of innovation effectively debars newcomers, whatever their potential talents, from becoming the Mozart of the new millennium.”

Gould is on to something about baseball, possibly about bacteria, but I’m not so sure about Bach. In baseball, Williams’ feat of 1941 would not be discussed today had he gotten three less hits at bat (the difference between .406 and .399 in his 185 hits out of 456 at bats). Would Williams have been deprived of at least one hit per 54 games by today’s players, who routinely dive and leap to steal what used to be sure hits? Definitely.

As for bacteria, Gould’s most vocal critics--philosopher Daniel Dennett and biologist Edward O. Wilson--will challenge Gould on his rejection of progress in evolution. They will need to provide evidence that small evolutionary sequences of life that can vary in either direction have a tendency to move to the right (more complex) rather than the left. They will also need to explain why the mechanism of natural selection would work to produce greater complexity rather than just local adaptations.

And Bach? Well, cultural relativists will be offended by Gould’s assumption that there is an outer wall for art and music. Is there? Who knows? How is it measured? There is no .400 equivalent in the arts.

So, our transcontinental cycling record, like most running, swimming and baseball records, is now hovering near an absolute outer wall of human perfection. Liquid diets, aerodynamic equipment, specialized training and experienced strategies every year take the best cyclists near this upper wall. And along with them, mediocre athletes are now shattering what used to be “unbreakable” marks. The transcontinental record, like .400 hitting, will be broken, but not often and not by much. The house is rather full now, the spread of excellence has narrowed and is approaching that outer wall, and the truly great must work extra hard to stand out. But somehow, they do.