One studies the genetic clues from ancient species to learn why they thrived and faltered. The other analyzes the inexorable climatic shifts that drive many of these species to extinction.

Already well-known in their fields, both were thrust onto a larger stage yesterday.

Beth Shapiro, an evolutionary biologist at Pennsylvania State University, and Daniel Sigman, a climate researcher at Princeton, are among 24 recipients this year of a MacArthur Foundation fellowship.

Informally called "genius" grants - though the foundation discourages that term - the awards go to people from a broad range of disciplines in the arts and sciences. Each wins $500,000 with no strings attached; typically the recipients have no idea they are under consideration until they have won.

Sigman, 40, seeks to understand why the world's climate was plunged into periodic ice ages over the last several million years. He has found that algae played a profound role - capturing carbon dioxide that would otherwise escape from the ocean to the atmosphere.

Shapiro, 33, spends her summers gathering fossils in the Arctic, then scrutinizes the genetic material for evidence as to why the species lived or died over time.

When she learned of the honor a week ago, she was skeptical.

"I thought it was one of my friends playing some sort of elaborate practical joke," Shapiro said.

The award money is spread over five years. Recipients are chosen for their unusual creativity and the promise of future achievement. Candidates are nominated by a rotating, confidential pool of experts in the humanities and sciences.

Princeton can lay claim to a second winner this year. Engineer Theodore Zoli, 43, designs bridges in the New York office of HNTB Corp., but he also teaches at Princeton as a visiting lecturer.

The foundation recognized him for ensuring the structural integrity of daring, modern bridge designs, as well as retrofitting old bridges to guard against terrorist threats.

Other winners include novelist Edwidge Danticat, who draws inspiration from her native Haiti, and investigative reporter Jerry Mitchell, who has pursued unsolved murders from the civil rights era. Since 1981, the foundation has bestowed about $300 million on 805 fellows.

Shapiro, among the youngest of this year's 24, has already contributed to six papers in Science, the nation's leading scientific journal.

Her main area of study - ancient DNA - is small, with fewer than a dozen labs worldwide focusing primarily on the topic. The field is also fairly new, fiercely competitive and marked by controversy.

Some early dramatic finds have since been discredited, as later researchers showed the supposed DNA from extinct creatures was the result of modern contamination.

Shapiro is among the most cautious and skeptical of the lot, said Robert Wayne, an evolutionary biologist at the University of California, Los Angeles. "That has, I think, gained her some enemies," Wayne said.

Shapiro acknowledges as much, attributing her caution to a firm understanding of the complex statistics involved.

She is among those who have publicly cast doubt on claims that protein fragments were recovered from dinosaurs.

She also has written papers on creatures ranging from the dodo - finding that the extinct flightless bird was related to pigeons - to bison. She spent this past summer in the Canadian Yukon and, though she'll have a 6-month-old baby in tow, is headed back next year.

"It's us, and some bones, and about six billion mosquitoes," said Shapiro, an Allentown native who was a Rhodes scholar in 1999.