Every Sperm Whale Alive Today May Have Descended From the Same Female

There’s no denying that sperm whales are amazing. As some of Earth’s largest mammals, they have the largest brain of any creature on the planet and can weigh up to 45 tons. But it turns out that the most impressive secrets of these huge animals are found in something much smaller: Their DNA. As John R. Platt writes for Hakai Magazine, modern sperm whales seem to have all descended from a single female.

A new study published in the journal Molecular Ecology reveals that deep within sperm whale’s mitochondrial DNA—genes passed on from mother to child—lie connections to a single, “Eve”-like whale.

The researchers analyzed mitochondrial DNA from 1,633 whales and found low genetic diversity. But that was no surprise: Past research has demonstrated that many of what scientists call “megafauna” (really big animals) aren’t that genetically diverse.

In 2002, for example, researchers found that killer whales lack diversity in their genes despite their large population size—likely due to some past event that once dramatically reduced their population. It turns out that other species lack diversity, too, because of everything from preferences for the same breeding grounds to loyalty to a certain kind of food.

So the study’s lead author, Alana Alexander, expected to find low diversity, Platt reports. But she found even lower diversity than she imagined. More data didn’t help uncover more diversity—instead, it confirmed ties to a single female whale who, at some point in the last 80,000 years, became the “mother” of all sperm whales who followed.

Though it would make sense to have a single mother in a single area—an ancestor who, say, really loved the Pacific Ocean—this mom’s genes have been found in sperm whales all over the world.

How this happened remains unknown and is even stranger given sperm whales’ social structures. Sperm whales are matrilineal, meaning most females stick together and males come and go, which would limit how far a female's genes could travel.

Yet these social structures now restrict the ability of sperm whales to differentiate and prevent new DNA from getting into the stream. Right now, it seems that sperm whale populations are “shaped by females being ‘home-bodies’—at the social group, regional and oceanic level,” Alexander said in a release. 

This lack of diversity leaves the whales more susceptible to things like climate change that disturb their preferred habitat. This, in turn, can also threaten future diversity, preventing the whales from straying too far from their region and mixing with others.

Sperm whales may have an elusive “Eve,” but today’s moms will need to get out more for the sake of their species.

Erin Blakemore | | READ MORE

Erin Blakemore is a Boulder, Colorado-based journalist. Her work has appeared in publications like The Washington Post, TIME, mental_floss, Popular Science and JSTOR Daily. Learn more at erinblakemore.com.