That’s because the genes in the cambium contain no program for senescence, or death, they say, but continue their program for making defenses even after hundreds of years. Old trees also produce just as many seeds and their leaves are just as resourceful as those of young trees. Though it has yet to be tested, the researchers believe other old trees — think of the 4,800-year-old bristlecone known as Methuselah in eastern California — may have a similar pattern of genetic programming.

Although ginkgos live long, they do age. The trees grow up and out: Up, with a cell-generating region called the apical meristem, and out, with the vascular cambium. Over time, weather or other things damage the apical meristem, limiting a tree’s height. And each year, leaves die and fall off.

But the cambium, contained within the tree’s trunk, remains intact and active. Cell division tends to slow down after the age of 200, they found. But the cells are still viable. They generate defenses and carry water and nutrients so the tree grows and stays healthy.

Sometimes trees may be reduced to just hollow stumps, but with the cambium intact, they can still produce leaves and flowers or even live as stumps.

Eventually, even ginkgo trees die. But a big question remains: Why?

Essentially, trees like ginkgo could live forever, says Peter Brown, a biologist who runs Rocky Mountain Tree Ring Research and was not involved in the study. “Being modular organisms, every year they’re putting on new wood, new roots, new leaves, new sex organs,” he said. “They’re not like an animal, like us. Once we’re born, all of our parts are there, and at a certain point they just start to give out on us.”