Unusual experiments on organs recovered from three carcasses suggest how baleen whales call out at sea.People have told stories of strange underwater sounds for thousands of years, but it took until the mid-20th century for scientists to pinpoint one of the causes: whales, singing and whistling and squeaking in the blue.The means by which some whales make these sounds has remained a mystery. A study published Wednesday in the journal Nature puts forth a new explanation, discovered thanks to a contraption that forced air through the voice boxes of three dead whales.The voice box, or larynx, is an ancient organ. “It evolved when fish crawled out of the sea and animals needed a way to separate the air they’re breathing from the food they’re taking in,” said Coen Elemans, an author of the study and a professor of biology at the University of Southern Denmark.The larynx functions like an antechamber to the windpipe, or trachea, with a flap of tissue called the epiglottis keeping food and drink from falling down the windpipe. A bit below the epiglottis, mammals have evolved additional folds of tissue, called vocal cords or vocal folds, which produce sounds when air exhaled from the lungs causes them to vibrate.When the land-dwelling ancestors of whales returned to life in the sea, “they basically had to change the larynx, because when these animals are breathing on the surface, they need to expel lots of air really fast,” Dr. Elemans said. Vocal folds like those of land mammals could get in the way.A view into the larynx of a humpback whale during the experiments. In the circle at left, the fatty cushion is at top, and at right and left are the vocal folds. Air forced between the folds and the cushion can produce sound.Coen P.H. Elemans, University of Southern DenmarkWe are having trouble retrieving the article content.Please enable JavaScript in your browser settings.Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.Thank you for your patience while we verify access.Already a subscriber? Log in.Want all of The Times? Subscribe.

Experiments using mice found a malfunction in adult stem cells that offers insights into why we turn into silver foxes and vixens.Many of the signs of aging are invisible, slow, and subtle — changes in cell division capacity, cardiac output and kidney function don’t exactly show up in the mirror. But gray hairs are one of the most obvious clues that the body isn’t working like it used to.Our hair turns gray when melanin-producing stem cells stop functioning properly. A new study in mice, but with implications for people and published Wednesday in the journal Nature, provides a clearer picture of the cellular glitches that turn us into silver foxes and vixens.“This is a really big step toward understanding why we gray,” said Mayumi Ito, an author of the study and a dermatology professor at New York University’s Grossman School of Medicine.Unlike embryonic stem cells, which develop into all sorts of different organs, adult stem cells have a more set path. The melanocyte stem cells in our hair follicles are responsible for producing and maintaining the pigment in our hair.Each hair follicle keeps immature melanocyte stem cells in storage. When they’re needed, those cells travel from one part of the follicle to another, where proteins spur them to mature into pigment-producing cells, giving hair its hue.Scientists assumed that gray hair was the result of that pool of melanocyte stem cells running dry. However, previous studies with mice made Dr. Ito and her co-author, Qi Sun, wonder if hair could lose its pigment even when stem cells are still present.Each hair follicle keeps immature melanocyte stem cells in storage, left. When they’re needed, those cells travel from one part of the follicle to another, where proteins spur them to mature into pigment-producing cells, giving hair its hue, right.NatureTo learn more about stem cell behavior throughout different phases of hair growth, the researchers spent two years tracking and imaging individual cells in mouse fur. To their amazement, the stem cells traveled back and forth within the hair follicle, transitioning into their mature, pigment-producing state and then out of it again.“We were surprised,” said Dr. Sun, who said seeing one group of stem cells switching back and forth between mature and young states did not match up with existing explanations.But as time wore on, the melanocyte cells couldn’t keep up the double act. A hair falling out and growing back takes a toll on the follicle, and eventually, the stem cells stopped making their journey, and thus, stopped receiving protein signals to make pigment. From then on, the new hair growth didn’t get its dose of melanin.The researchers further explored this effect by plucking hairs from mice, simulating a faster hair growth cycle. This “forced aging” led to a buildup of melanocyte stem cells stuck in their storage place, no longer producing melanin. The mice’s fur went from dark brown to salt-and-pepper.While the study was conducted with rodents, the researchers say their findings should be relevant to how human hair gets and loses its color. What’s more, they hope their findings could be a step toward preventing or reversing the graying process.Melissa Harris, a biologist at the University of Alabama at Birmingham who was not involved with the study, said the findings help “clinch” previous evidence she’s seen suggesting that “not all melanocyte stem cells are created equal, and even if you have some left over, they may not be useful.”Dr. Harris said she takes the study’s findings about its “forced aging” of mouse hair “with maybe a little bit of a grain of salt,” as a plucked hair might not behave the same as naturally aged hair. But she found the study valuable, not just because a cure for graying hair might be a hit with the public; the insights into stem cell behavior might help researchers understand things like cancer and cell regeneration.“I think sometimes people take the hair for granted,” she said, “but in a sense, it makes it actually really easy for us to see potential ways in which aging or other perturbations affect our bodies.”

An experiment revealed that chomping on slightly tougher material requires markedly more energy. Spending less time on mastication may go hand in hand with human evolution.Humans spend about 35 minutes every day chewing. That adds up to more than a full week out of every year. But that’s nothing compared to the time spent masticating by our cousins: Chimps chew for 4.5 hours a day, and orangutans clock 6.6 hours.The differences between our chewing habits and those of our closest relatives offer insights into human evolution. A study published Wednesday in the journal Science Advances explores how much energy people use while chewing, and how that may have guided — or been guided by — our gradual transformation into modern humans.Chewing, in addition to keeping us from choking, makes the energy and nutrients in food accessible to the digestive system. But the very act of chewing requires us to expend energy. Adaptations to teeth, jaws and muscles all play a part in how efficiently humans chew.Adam van Casteren, an author of the new study and a research associate at the University of Manchester in England, says that scientists haven’t delved too deeply into the energetic costs of chewing partly because compared with other things we do, such as walking or running, it’s a thin slice of the energy-use pie. But even comparatively small advantages can play a big role in evolution, and he wanted to find out if that might be the case with chewing.To measure the energy that goes into chewing, Dr. van Casteren and his colleagues outfitted study participants with plastic hoods that look like “an astronaut’s helmet,” he said. The hoods were connected to tubes to measure oxygen and carbon dioxide from breathing. Because metabolic processes are fueled by oxygen and produce carbon dioxide, gas exchange can be a useful measure for how much energy something takes. The researchers then gave the subjects gum.The participants didn’t get the sugary kind, though; the gum bases they chewed were flavorless and odorless. Digestive systems respond to flavors and scents, so the researchers wanted to make sure they were only measuring the energy associated with chewing and not the energy of a stomach gearing up for a tasty meal.Measuring the chewing muscles with an ultrasound wand.Amanda HenryThe test subjects chewed two pieces of gum, one hard and one soft, for 15 minutes each. The results surprised researchers. The softer gum raised the participants’ metabolic rates about 10 percent higher than when they were resting; the harder gum caused a 15 percent increase.“I thought there wasn’t going to be as big a difference,” Dr. van Casteren said. “Very small changes in the material properties of the item you’re chewing can cause quite substantial increases in energy expenditure, and that opens up a whole universe of questions.”Because chewing tougher food — or in this case, tougher gum — takes significantly more energy, these findings suggest that the metabolic costs of chewing may have played an important role in our evolution. Making food easier to process through cooking, mashing food with tools and growing crops optimized for eating might have dialed down the evolutionary pressure for us to be super-chewers. Our evolving chewing needs may have even shaped what our faces look like.“One thing that we haven’t really been able to figure out is why the human skull is so funny-looking,” said Justin Ledogar, a biological anthropologist at East Tennessee State University, who was not involved with the study. Compared to our closest relatives, our facial skeletons are delicately built with jaws, teeth and chewing muscles that are all relatively small. “All this reflects a reduced reliance on forceful chewing,” he explained.But he added that our flatter faces and shorter jaws let us bite more efficiently. “It makes the whole process of feeding just metabolically less costly,” Dr. Ledogar said. Humans developed ways to chew smarter, not harder. Dr. van Casteren, who hopes to continue his research using actual foods, says he’s excited by the prospect of learning more about how humans evolved.“To know about the environmental and societal and dietary causes that led us to get here, it’s just infinitely interesting to me,” he said, because it enables humankind to “try and work out the foggy road ahead.”