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. ||||| Adult whale Lulu was one of UK’s last resident pod and had never produced a calf, probably because pollutants in her blubber had caused infertility 
 
 One of the highest concentrations of toxic pollutants ever recorded in a marine mammal has been revealed in a Scottish killer whale that died in 2016. 
 
 The adult whale, known as Lulu, was a member of the UK’s last resident pod and a postmortem also showed she had never produced a calf. The pollutants, called PCBs, are known to cause infertility and these latest findings add to strong evidence that the pod is doomed to extinction. 
 
 The level of PCBs found in Lulu’s blubber were extreme at 950mg/kg, more than 100 times the 9mg/kg limit above which damage to the health of marine mammals is known to occur. A 2016 analysis showed the average concentration for killer whales in the north-east Atlantic was about 150mg/kg. 
 
 'Extraordinary' levels of pollutants found in 10km deep Mariana trench Read more 
 
 Lulu died after becoming tangled in ropes used to haul up creels, the netted cages used to catch lobsters and crabs. But Andrew Brownlow, head of the Scottish Marine Animal Stranding Scheme, said: “Given what is known about the toxic effects of PCBs, we have to consider that such a high-pollutant burden could have been affecting her health and reproductive fitness.” 
 
 Brownlow, also a veterinary pathologist at Scotland’s Rural College, said: “Lulu’s apparent infertility is an ominous finding – with no new animals being born, it is now looking increasingly likely that this small group will eventually go extinct. One of the factors in this groups apparent failure to reproduce could be their high burden of organic pollutants.” 
 
 The examination of Lulu found she was at least 20 years old, well above the age of sexual maturity, which ranges from six to 10 years old. However, analysis of the ovaries shows she never bore a calf. The entire pod may have been left barren, as no calf has ever been seen in the 23 years the group have been monitored. 
 
 PCBs were used for decades in electrical equipment but finally banned in the 1980s after the full toxic impacts on people and wildlife were revealed. PCBs, which cause cancers and suppress the immune system, are especially harmful to top predators because they accumulate in fat up the food chain. Killer whales can live for many decades, meaning they can end up with very high levels of PCBs. 
 
 Tilikum and Granny are dead. Here’s why you should care about these killer whales | Patrick Barkham Read more 
 
 PCBs are extremely tough chemicals and do not break down in the environment. The decline in PCB levels in marine wildlife seen after the 1980s ban has now levelled off in some places, indicating that the toxic chemicals are still leaking into the oceans from inadequate waste storage sites. 
 
 “Once PCBs get into the marine environment, they are difficult if not impossible to remove,” said Brownlow. “There are still many PCB stockpiles in Europe, and it is absolutely essential that these toxic reserves do not reach the marine environment.” 
 
 Bottlenose dolphins in the north-east Atlantic have also shown both high PCB levels and low reproductive rates. Other PCBs hotspots around the world include the entire Mediterranean and the Black Sea, while specific populations suffering from PCB poisoning include belugas in Canada and polar bears across the Arctic. 
 
 In February, scientists discovered “extraordinary” amounts of PCBs had even reached the most remote and inaccessible place on the planet – the 10km deep Mariana trench in the Pacific Ocean.
– 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.)