Sharks are among the best swimmers on the planet, but a new research suggests that even they sometimes “hold their breath” while diving deep underwater. The reason is that sharks are cold-blooded and their body temperature matches the waters they swim in. To do deep dives, they must maintain body heat, and the best way to do that is to close their gills (鳃).

Royer, a leading researcher at the University of Hawaii, set out to study the diving habits of hammerheads sharks. They’re known for swimming in warmer coastal waters, but earlier studies showed they can also dive to over 800 meters below the surface. At those cold depths, the water temperature falls to as low as 5℃.

For these sharks, the fall in temperature is a matter of life and death. Because a shark can’t produce its own body heat, it begins to freeze the deeper it goes. Its muscles, eyes and brain become sluggish (迟钝). If it gets too cold, it can’t swim. And if it stops swimming, water doesn’t go across its gills. It can’t breathe and will eventually drown (溺亡).

How is it that hammerheads are able to go down into these deep depths and survive? To find out, Royer and his colleagues caught the fish and attached an electronic sensor to each shark. The sensor would release itself from the shark’s body after several weeks. The data they found amazed them: The sharks dived, spent just a few minutes at depths and then they shot towards the surface. They closed their gills and kept water out of their gills so that their body wouldn’t cool down.

“Unlike animals with lungs, the sharks don’t return to the surface to breathe. Instead, they simply go to a depth where it’s warm enough for them to feel comfortable and reopen their gills. Hammerheads are probably not the only species doing so. Our work is another example of how new electronic sensors help to explain the extraordinary ability of these animals across 400 million years of changing ocean environments,” Royer said.

We are the products of evolution, and not just evolution that occurred billions of years ago. As scientists look deeper into our genes (基因), they are finding examples of human evolution in just the past few thousand years. People in Ethiopian highlands have adapted to living at high altitudes. Cattle -raising people in East Africa and northern Europe have gained a mutation (突变) that helps them digest milk as adults.

On Thursday in an article published in Cell, a team of researchers reported a new kind of adaptation - not to air or to food, but to the ocean. A group of sea-dwelling people in Southeast Asia have evolved into better divers. The Bajau, as these people are known, number in the hundreds of thousands in Indonesia, Malaysia and the Philippines. They have traditionally lived on houseboats; in recent times, they’ve also built houses on stilts (支柱) in coastal waters. “They are simply a stranger to the land,” said Redney C. Jubilado, a University of Hawaii researcher who studies the Bajau.

Dr. Jubilado first met the Bajau while growing up on Samal Island in the Philippines. They made a living as divers, spearfishing or harvesting shellfish. “We were so amazed that they could stay underwater much longer than us local islanders,” Dr. Jubilado said. “I could see them actually walking under the sea.”

In 2015, Melissa Ilardo, then a graduate student in genetics at the University of Copenhagen, heard about the Bajau. She wondered if centuries of diving could have led to the evolution of physical characteristics that made the task easier for them. “It seemed like the perfect chance for natural selection to act on a population,” said Dr. Ilardo. She also said there were likely a number of other genes that help the Bajau dive.

Most Helpful Apps for Students

There's almost an app for everything nowadays, and this can make student life easier, cheaper, safer and more fun. Whether you want help with taking notes, revising, waking up on time or keeping fit， read on for our student app picks．

Just a few years ago, students attending lectures would have to spend the entire time writing wildly on notepads, in order not to miss any vital bit of information. Then along came technology, and now， lecture recording apps are a reality.

Sound Note is a popular lecture recording app for iPad users. You can store an entire lecture in both visual and audio form. Other good quality lecture recording apps include Notes Plus and Audio Memos Free—The Voice Recorder.

Organization is key for success and well-being at university, and student planner apps are becoming increasingly popular. As well as saving on paper, many student planner apps also send reminders and warnings straight to your phone or device. Popular student planner apps include Timetable, My Class Schedule and Class Timetable.

A number of apps for students have been developed promoting personal safety if out alone at night. The Circle of Six app is particularly useful for locating lost friends on nights out and also allows users to send their circle of six friends an instant call for help at the touch of a button. The GPS tracker will mark your location on your friends" devices, ensuring you'll always be able to find one another if necessary. Other student apps that promote safety include bSafe and React Mobile.

If you're interested in eating healthily while keeping to a student budget, consider downloading a few healthy eating apps. Examples I've come across which are perfect apps for students include Rockin Ramen， a student app featuring a number of nutritious recipes with Ramen as a main ingredient, and MealBoard, an app which plans healthy meals, grocery shops and recipes based on what you've got in the fridge.