When it comes to saving a life on the planet, Noah's method of keeping just two of each species isn't enough to save most from extinction.

In fact, even moderately sized populations could die out in a climate-changed Earth, according to new research.

In the first-of-its-kind study published in the journal Proceedings of the Royal Society B on Tuesday, June 11, researchers from the University of Vermont revealed that most species need large populations to survive extinction.

An Urchin's Rare Genetic Variant

To reach their conclusions, the team led by biologist Melissa Pespeni experimented on hundreds of thousands of purple sea urchin larvae to see how they respond to seawater that was deliberately made moderately or extremely acidic.

It turns out there's a rare genetic variation in a small number of sea urchins that is very useful for survival. Pespeni described the genetic variants as "like having one winter coat among fifty lightweight jackets when the weather hits twenty below in Vermont."

In extremely acidic seawater, these rare variants increased in frequency in the larvae. These genes allow the next generation of urchins alter how certain proteins function, including the proteins they use to make their shells and the ones that help them manage their cells' acidity.

However, for the sea urchins to maintain these rare variants in their DNA, their population count needs to be high.

"The bigger the population, the more rare variation you'll have," explained lead author Reid Brennan, who is a post-doctoral researcher in Pespeni's UVM lab. "If we reduce population sizes, then we're going to have less fodder for evolution-and less chance to have the rare genetic variation that might be beneficial."

According to the authors, this means that while some organisms may persist in a climate-changed environment due to their ability to change their physiology, most animals will only survive by evolution.

The Future Of Purple Sea Urchins

A recent United Nations report says that about a million species of animals and plants are at risk of extinction due to human activity, including climate change.

For now, Brennan assured that this particular species of sea urchin will be safe from extinction in the short term. After all, they have the genetic heritage of adapting to extremely acidic seawater as well as the genetic variation necessary to evolve.

However, she noted, their findings also mean that it's important for humans to do their part in keeping their habitats and populations protected so that the species maintain their valuable genetic variants.

"This discovery has important implications for long-term species persistence," Pespeni said. "These rare variants are a kind of currency that urchins have to spend. But they can only spend it once."

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