Biology / Professor Daniel Martinez
The Immortal Hydra

By Janice Ma '11

Moving across the country with a U-Haul truck, Biology Professor Daniel Martínez took pains to protect his precious cargo of 60 hydra specimens that might just live forever under the right conditions. The aging—or lack thereof—of these tiny, freshwater polyps had become his research obsession, and Martínez wanted to make sure that none of his specimens died of unnatural causes before he reached his new role at a hydra lab in Irvine.

With the Petri dishes carefully packed in his cooler, Martínez regularly fed the hydra freshly hatched brine shrimp, cleaned their containers and constantly maintained the cooler temperature with ice. “I remember in Zion National Park I was feeding them at night and then in the morning I was washing them,” Martínez says. “People thought I was crazy, like ‘What are all these little Petri dishes with hydra?’”

Martínez was set on seeing if hydra escaped the aging that was inevitable for all other animals. He first heard rumors of the hydra’s immortality when he was completing his Ph.D. at the State University of New York, Stony Brook. But there were no experiments being conducted to prove the claim.

“I said ‘no way,’” Martínez recalls. “There’s no way that any animal can be immortal. Evolutionary theory says that all multi-cellular creatures should age. So I said, ‘Well, I’m going to prove them wrong. I’m going to prove that hydra age like all animals.’”

For Martínez and other biologists, aging is not just defined by physical signs like graying hair or by death from external causes like disease or accidents. “There’s nothing universally quantifiable for aging,” Martínez says. “So probably the best [measure of aging] is increased mortality, because that’s a clear sign.” Almost all living organisms have a mortality trajectory with a point where creatures naturally start to die at a much higher rate than before. Except for hydra.

After arriving at Irvine with his hydra alive and thriving, Martínez continued the experiment for four years. Almost no hydra died. Although Martínez put his hydra to sleep when he moved to Pomona College, he saved their bodies and published his results.

“For a creature the size of hydra, [a near-zero mortality] after four years is significant because normally things that are small don’t live very long,” Martínez says. “So basically, I was trying to prove that hydra did age, and by the end I was convinced that they didn’t.”

While four years may seem like nothing to us, it is an astonishingly long time for a creature as small as the hydra, which ranges from 0.25 to 2.5 centimeters in length. It also defies the normal correlation between the aging of an organism and its reproductive behavior, which shows that organisms that reproduce later and less frequently tend to live longer.

Hydra, on the other hand, start reproducing almost immediately and continue to reproduce frequently. Their predicted lifespan, according to this correlation, should only be several months. So it’s no surprise that their four-year-plus life span deviates drastically from a general pattern that over 99 percent of multi-cellular organisms follow.

This aberration turned out to be so compelling that the Max Planck Institute for Demographic Research in Rostock, Germany requested Martínez to restart the experiment with their funding. Martínez has now been following another set of hydra, collected from all over the world, for the past two and a half years. His lab has set optimal conditions for these hydra by controlling temperature, feeding them, and isolating them from other hydra.

So far the hydra have shown the same results that Martínez first found—almost zero-mortality. While it will take more time to be certain whether these hydra will age and eventually die, Martínez already has a hypothesis on why they have lived so long. “Hydra is a bag of stem cells,” he says. “It is an adult that is produced by embryonic cells, so it is really a perennial embryo. The genes that regulate development are constantly on, so they are constantly rejuvenating the body.”

This remarkable trait of the hydra leads to a related phenomenon that may lie behind its possible immortality— regeneration. The hydra has “an amazing regeneration ability that allows it to escape aging,” Martínez says. “I can take a hundred hydra, make a cell suspension, dissociate all the tissue, put it in a centrifuge, make it into a bowl. …That bowl will generate into a few hydra. I mean, I’m making a pellet, and from that I will get an animal.”

But despite the genetic similarities between hydra and humans, Martínez is skeptical of his results being applicable to the process of human aging as well. “We are very different animals,” he says. “We are a lot more sophisticated, a lot more complex, we have organs. But there’s a price that you pay.”