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.

Princeton's Sigman, on the other hand, draws his knowledge from pieces of ancient seafloor.

It has been well accepted that ice ages are triggered when changes in Earth's axis of rotation alter the distribution of sunlight over the planet. But that alone cannot explain the dramatic buildup and melting of ice sheets every 20,000 years or so, he said.

One important piece of the puzzle is the familiar greenhouse gas carbon dioxide. Studies of the air bubbles trapped in ice cores show that carbon dioxide rose and fell with the temperature over the last 800,000 years. The carbon dioxide would have amplified the warming, he said. But that does not explain what was driving the carbon dioxide up and down.

Some of it is chemistry: A cooler climate makes carbon dioxide more soluble in the oceans. But algae also matter - particularly in the Southern Ocean - near Antarctica, where mixing patterns push deep water up to the surface and allow dissolved carbon dioxide to "leak" back in the atmosphere.

That's where the algae come in. When they grow more abundant, they stop this leak by sequestering more carbon dioxide, he said.

To trace the long-term history of algae, Sigman is looking at pieces of ancient seafloor, where algae leave traces of their activity in the form of nitrogen. The quest suits him well, he said, because the work involves biology and physics.

Now, though he is not officially trained as a microbiologist, he grows bacteria in his lab and feeds them pieces of ancient seafloor. The bacteria release nitrogen from the sediment, turning into a gas that he can run through his instruments. That can show what was occurring with the algae in different eras of the past.

He and Shapiro say they will spend the money on research. As with all recipients, the foundation did not tell them they were candidates.

Even the way Shapiro was notified was a bit mysterious.

A week ago, the biologist was expecting to meet with a young woman who sought a graduate position in her lab.

But at the appointed time, Shapiro got a phone call from a foundation official telling her she had won.

After recovering, she started to send an e-mail to the young woman, who still had not appeared.

Only later did the MacArthur people call back to say that the job applicant was not real; they had invented her to ensure that Shapiro would be in her office.

MacArthur's 24 Winners

Lynsey Addario, 35, photojournalist,

Istanbul, Turkey.

Maneesh Agrawala, 37, computer vision technologist,

Berkeley, Calif.

Timothy Barrett, 59, Iowa City, Iowa. A papermaker and paper historian.

Mark Bradford, 47,

Los Angeles.

Mixed-media artist.

Edwidge Danticat, 40,

Miami. Novelist.

Rackstraw Downes, 69,

New York. Painter, former Penn art professor.

Esther Duflo, 36, Cambridge, Mass. Economist who analyzes poverty in South Asia

and Africa.

Deborah Eisenberg, 63, New York. Short-story writer.

Lin He, 35, Berkeley, Calif. Molecular biologist uncovering the role of microRNAs in cancer.

Peter Huybers, 35, Cambridge, Mass.

Climate scientist.

James Longley, 37,

Seattle. Filmmaker

of Middle East conflicts.

L. Mahadevan, 44, Cambridge, Mass.

Applied mathematician.

Heather McHugh, 61, Seattle. Poet.

Jerry Mitchell, 50, Jackson, Miss. Investigative newspaper reporter.

Rebecca Onie, 32, Boston. Links college volunteers with medical professionals to improve health care for low-income patients.

Richard Prum, 48,

New Haven, Conn. Ornithologist.

John A. Rogers, 42, Urbana, Ill. An applied physicist.

Elyn Saks, 43, Los Angeles. A law-school professor who has struggled with schizophrenia.

Jill Seaman, 57, Old Fangak, Sudan. Physician in an impoverished area

of southern Sudan.

Beth Shapiro, 33,

University Park, Pa. Evolutionary biologist.

Daniel Sigman, 40, Princeton, N.J. Biogeochemist.

Mary Tinetti, 58,

New Haven, Conn. Geriatric physician.

Camille Utterback, 39,

San Francisco. Artist who uses digital technologies.

Theodore Zoli, 43, New York. Bridge engineer.

SOURCE: John D. and Catherine T. MacArthur Foundation.

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See more on the program and the winners via http://go.philly.com/genius09 EndText

Contact staff writer Tom Avril at 215-854-2430 or tavril@phillynews.com.