As Langdon loaded his slide projector, he explained that the number PHI was derived from the Fibonacci sequence—a progression famous not only because the sum of adjacent terms equaled the next term, but because the quotients of adjacent terms possessed the astonishing property of approaching the number 1.618—PHI!

Despite PHI's seemingly mystical mathematical origins, Langdon explained, the truly mind-boggling aspect of PHI was its role as a fundamental building block in nature. Plants, animals, and even human beings all possessed dimensional properties that adhered with eerie exactitude to the ratio of PHI to 1.

"PHI's ubiquity in nature," Langdon said, killing the lights, "clearly exceeds coincidence, and so the ancients assumed the number PHI must have been preordained by the Creator of the universe. Early scientists heralded one-point-six-one-eight as the Divine Proportion."

"Hold on," said a young woman in the front row. "I'm a bio major and I've never seen this Divine Proportion in nature."

"No?" Langdon grinned. "Ever study the relationship between females and males in a honeybee community?"

"Sure. The female bees always outnumber the male bees."

"Correct. And did you know that if you divide the number of female bees by the number of male bees in any beehive in the world, you always get the same number?"