Studying Seemingly Immortal Lichens, in a Place for the Dead

In this bucolic cemetery, steps from the headquarters of Harvard’s research forest, she was pondering mortality. But she wasn’t thinking about the Frenches. She was thinking about lichens.

Pale green and vaguely ruffled, like calcified doilies, lichens grow all over the tombstones and the old stone walls that fringe properties in this part of the world. Most people barely notice them. But Dr. Pringle, a mycologist at Harvard, believes they may help answer one of science’s greatest questions: Is immortality biologically possible?

For eight years, Dr. Pringle, 42, has been returning to this cemetery each fall, to measure, sketch and scrutinize the lichens, which belong to the genus Xanthoparmelia. She wants to know whether they deteriorate with the passage of time, leaving them more susceptible to death.

Biologists call it senescence: the grim reality of decline with age. Are the lichens more likely to break apart as the years pass? Does their chemistry or bacterial composition change, leaving them more vulnerable to pathogens?

Lichens are not individuals but tiny ecosystems, composed of one main fungus, a group of algae and an assortment of smaller fungi and bacteria. To reproduce, they can either launch a single fungal spore that must then find new algae to join with, or they can send out fingerlike projections called isidia, which contain the whole lichen package and need only a nice rock to land on.

Once attached, they hardly lead a carefree life. They may face chemical warfare from neighboring lichens, as well as the menace of a hard rain.

While lichens are communities, Dr. Pringle is largely interested in the fungi. Mycologists, the scientists who study fungi — not the most glamorous corridor of biology — have long assumed that many of these organisms don’t age.

The clear exception is yeast, a single-cell fungus that does senesce and that researchers use as a model to study aging. But most multicellular fungi, the assumption goes, don’t senesce.

No one has ever proved that, though, or even collected much data. The belief in fungi everlasting has been buoyed in part by Armillaria bulbosa, a species known as the “humongous fungus,” which grows to be as heavy as a blue whale and can take over acres of forest. (Crystal Falls, Mich., holds an annual Humongous Fungus festival, complete with the world’s largest mushroom pizza, to celebrate a 38-acre, 1,000-ton Armillaria that grows nearby and is thought to be 1,500 to 10,000 years old.)

Does that mean Armillaria and many of the world’s other fungi are not aging? Some experts believe it does. If true, such organisms would be the fungal equivalent of vampires, able to die only by external means. (“A bus can still run over them,” Dr. Pringle said.) But the concept has yet to catch on in the wider world of biology, dominated by scientists who study plants and animals.

In the world beyond fungi, whether organisms can escape aging is a matter of scientific controversy. A longstanding explanation for aging pins the blame on built-up genetic mutations activated once fertility begins to taper off. But this theory doesn’t work for fungi, which reproduce more, not less, as they grow older.

According to a second theory, aging occurs because some traits that make us more reproductively successful may also set the stage for our demise. High testosterone levels, for instance, might help males make more babies — but also predispose them to prostate cancer.

Both theories explain aging as a biological imperative, a cellular commandment no life form can escape. Dr. Pringle says that way of looking at the world does not account for the realities of life as a fungus.

“What you know is based on the organisms you study,” she said. “What would you say about the evolution of senescence if instead of working with insects, you worked with modular organisms, which is what lichen are?”

Daniel Doak, a University of Colorado ecologist, agrees that the question is worth asking. Research like Dr. Pringle’s — along with other studies of species including the bristlecone pine tree and the wandering albatross, a bird, both of which may avoid senescence — suggests another possible path.

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