text: 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. ||||| The interplay of natural selection and genetic drift, influenced by geographic isolation, mating systems and population size, determines patterns of genetic diversity within species. The sperm whale provides an interesting example of a long‐lived species with few geographic barriers to dispersal. Worldwide mtDNA diversity is relatively low, but highly structured among geographic regions and social groups, attributed to female philopatry. However, it is unclear whether this female philopatry is due to geographic regions or social groups, or how this might vary on a worldwide scale. To answer these questions, we combined mtDNA information for 1091 previously published samples with 542 newly obtained DNA profiles (394‐bp mtDNA, sex, 13 microsatellites) including the previously unsampled Indian Ocean, and social group information for 541 individuals. We found low mtDNA diversity (π = 0.430%) reflecting an expansion event <80 000 years bp, but strong differentiation by ocean, among regions within some oceans, and among social groups. In comparison, microsatellite differentiation was low at all levels, presumably due to male‐mediated gene flow. A hierarchical amova showed that regions were important for explaining mtDNA variance in the Indian Ocean, but not Pacific, with social group sampling in the Atlantic too limited to include in analyses. Social groups were important in partitioning mtDNA and microsatellite variance within both oceans. Therefore, both geographic philopatry and social philopatry influence genetic structure in the sperm whale, but their relative importance differs by sex and ocean, reflecting breeding behaviour, geographic features and perhaps a more recent origin of sperm whales in the Pacific. By investigating the interplay of evolutionary forces operating at different temporal and geographic scales, we show that sperm whales are perhaps a unique example of a worldwide population expansion followed by rapid assortment due to female social organization.
target: – While investigating samples of toxic levels of heavy metals found in sperm whales, researchers stumbled upon a surprising discovery: All of today's sperm whales appear to have descended from the same female, reports Hakai magazine. They've named her Eve and say she lived between 10,000 and 80,000 years ago. In the journal Molecular Ecology, the researchers explain that the genetic diversity of the whales, one of the planet's largest animals, turns out to be even lower than previously thought. The key was locked away in the species' mitochondrial DNA, a type of DNA passed down through the generations from mothers, not fathers. Conducting genetic tests on 542 samples collected over the past six years by Ocean Alliance and comparing them to another 1,000 whales analyzed in the past 15 years, they found that a single female whale left her thumbprint on all of them. Which doesn't quite make sense given that mothers tend to dominate certain areas without moving around, so the spread of one set of genes across the globe would be unusual. Somewhere along the line one mother whale and her descendants were able to out-compete all other females alive at the time—perhaps there was a sudden global population decline, or female whale behavior was dramatically different then—and their genetic lineage took off. One drawback is that this lack of diversity makes the whales more susceptible to things such as climate change, notes Smithsonian, suggesting that "today’s moms will need to get out more for the sake of their species." (Check out what one diver was sprayed with when encountering a diving sperm whale.)