【推荐2】Tai chi, a traditional, slow-moving form of Chinese physical exercise, is known to increase flexibility and improve balance. New research has been conducted to determine whether tai chi has an influence on lowering blood pressure in people with prehypertension (高血压前期).

In the study, Chinese scientists put 342 adults with prehypertension into two groups. The average age of people taking part in the study was 49. About half the participants (参与者) took part in aerobic exercise, including jogging, climbing stairs and cycling. The other half was trained to practice tai chi. Both groups got hour-long exercises four times a week.

Nearly 22% of the people who practiced tai chi saw their blood pressure fall to be normal, compared with nearly 16% of people in the aerobic exercise group. And fewer patients in the tai chi group went on to develop high blood pressure than patients in the aerobic exercise group.

So what is it about tai chi that helps lower blood pressure? “The practice tends to get more of a response from the parasympathetic (副交感的) nervous system, which is the network of nerves that relaxes your body after periods of stress or danger,” says Ruth Taylor-Piliae, a professor at the University of Arizona’s College of Nursing.

“I think the beauty of tai chi is that you don’t have to have a special gym membership, you don’t have to have special clothing,” Taylor-Piliae says. “Once you learn tai chi, you can do it anytime and anyplace. And it does provide a calming and relaxing effect.”

Evidence suggests it can also help protect against cognitive fall and even improve memory. But you have to practice it continually to get the most benefit.

【推荐1】Researchers have found depression is linked to areas of the brain shrinking in size but when depression is paired with anxiety one area of the brain becomes greatly larger.

A new study, published in the Journal of Psychiatry and Neuroscience, looked at more than 10,000 people to find the effects of depression and anxiety on brain volume, The study shows depression has a pronounced impact on the hippocampus, the part of the brain linked to memory and learning, shrinking it.

In contrast, the study found that when depression and anxiety occur together, it leads to an increase in size of the part of the brain linked to emotions, the amygdala, “Many studies looking at the effects of depression on brain do not account for the fact that people who have depression often experience anxiety too,” study lead and Ph.D. researcher Ms. Daniela Oyarce said.

Depression is considered a serious medical condition worldwide, and one in six Ausualians currently experience depression, anxiety, or both, “We found people who have depression alone have lower brain volumes in many areas of the brain, and in particular the hippocampus,” Ms. Daniela Oyarce said. “This becomes even more relevant later in life because a smaller hippocampus is a risk factor for Alzheimer's disease and may speed the development of dementia.”

A particularly important finding of this research is that people who had both depression and anxiety had less shrinkage in many brain areas and even an increase in the amygdala. This indicates that the true effects of depression on the brain has been underestimated because of an opposite effect in the amygdala. “Anxiety lowers the effects of depression on brain volume sizes by three percent on average—somewhat hiding the true shrinking effects of depression,” Ms. Daniela Oyarce said.

“More research is needed into how anxiety lowers the effects of depression, but for the amygdala, perhaps anxiety leads to overactivity,” Ms. Daniela Oyarce added.

【推荐1】Between a quarter and one third of all marine species rely on coral reefs (珊瑚礁)at some point in their life cycle. The Great Barrier Reef, the world's largest coral reef, covers nearly 133,000 square miles and is home to more than 1,500 species of fish, 411 species of hard coral and dozens of other species.

Australian's Great Barrier Reef has lost 50% of its coral populations in the last three decades, with climate change a key driver of reef disturbance, a new study has found.

Researchers from the Centre of Excellence for Coral Reef Studies, in Queensland, northeastern Australia, studied coral communities and their colony size along the length of the Great Barrier Reef between 1995 and 2017, finding reduction of virtually all coral populations.

“We found the number of small, medium and large coral on the Great Barrier Reef has dropped by more than 50% since the 1990s," reported co-author Terry Hughes, a professor at the centre, in a statement.

Reefs are basic to the health of marine ecosystems — without them, ecosystems collapse, and marine life dies. Coral population sizes are also considered important when it comes to the coral's ability to reproduce." A coral population has millions of small, baby corals, as well as many large ones,“ said Andy Dietzel, a doctoral student in a statement. "Our results show the ability of the Great Barrier Reef to recover becomes weak compared to the past," he added.

Population falls occurred in both shallow and deep water coral species, experts found, but branching coral and table-shaped coral — which provide habitats for fish — were worst affected by mass bleaching （白化）events in 2016 and 2017, caused by record-breaking temperatures.

Warm ocean temperatures are the main driver of coral bleaching, when coral turns white as a stress response to water that is too warm. Bleaching doesn't kill coral immediately, but if temperatures remain high, eventually the coral will die, destroying a natural habitat for many species of marine life.

The new study found the serious worsening of coral colonies in the Northern and Central Great Barrier Reef following the mass bleaching events in the past five years, and experts said the southern part of the reef also suffered record-breaking temperatures in early 2020.

“We used to think the Great Barrier Reef is protected by its huge size — but our results show that even the world's largest and relatively well-protected reef system is increasingly dropping, Hughes said. He warned that climate change is driving an increase in the frequency of the reef disturbance like marine heat waves. "There is no time to lose — we must sharply reduce greenhouse gases as soon as possible," he said.

【推荐2】Nalini Nadkarni didn't play with Barbies as a girl. She was busy climbing the trees with unlimited energy in her yard in Maryland.

The forest ecologist might seem an unlikely person to help design and promote Barbies. But she's been inspiring girls worldwide to play with dolls having magnifying glasses (放大镜) and boots. It's through new explorer Barbie dolls designed with her input by Mattel and National Geographic. The dolls, including a conservationist, a biologist and a nature photojournalist, are long overdue, said Nadkarni, a biology professor. "As a child, I created my own fun by tree climbing. I could picture the treetop as a place of rescue, or as a hospital for wounded birds. It was my world, and I could be anything in it," she said.

In 2003, she thought of ways to further fire girls with love for science. “I asked myself, ‘What do girls care about when little?’ ” Nadkarni said. She looked to her young daughter. "I knew girls wanted to play with and look like Barbies. But what if Barbies had field clothes on and came with a little book about plants?"

She contacted Barbie-maker Mattel and was told that a "treetop Barbie" wouldn't sell, but she insisted. She finally created her own treetop dolls. Mattel agreed she could produce the dolls on a small scale (规模), and Nadkarni sold about 400. Last year, Nadkarni was thrilled to learn National Geographic worked with Mattel to come up with a line of adventure dolls, and that they wanted her to serve on their advisory committee.

Since sales began, Nadkarni has heard from girls coast to coast, thanking her and asking questions about how they can make a difference to help trees, "I love climbing trees and learning all I can about them. But getting children excited about protecting forests is one of the most important things I have done, " Nadkarni said.

【推荐3】After a five-year travel to study plants, animals and fossils (化石) in South America and on the islands in the Pacific, British naturalist Charles Darwin brought the idea of natural selection to the attention of the world in his best-selling book, On the Origin of Species.

Natural selection is the process through which populations of living organisms adapt and change naturally. Individuals in a population are naturally variable. In other words, they are all different in some ways. This variation means that some individuals have characteristics better suited to the environment than others. Individuals with adaptive characteristics — characteristics that give them some advantage-are more likely to survive and reproduce. These individuals then pass the adaptive characteristics on to their children. Over time, these characteristics become more common in the population. Through this process of natural selection, adaptive characteristics are passed on to the next generations. Those organisms that cannot adapt fast enough through natural selection will die out.

Natural selection can also lead to new and distinctly different species. It is one of the processes that drive phylogenesis and help to explain the diversity of life on Earth.

Darwin chose the name natural selection to contrast with artificial selection that is controlled by humans. Darwin and other scientists of his day argued that a process much like artificial selection happened in nature, without any human help. He argued that natural selection explained how a wide variety of life forms developed overtime from a single common ancestor.

Through studying the fossil record, we know that some species may not be able to adapt fast enough through natural selection and many of them that once lived on Earth are now extinct. Dinosaurs are one example. However, human actions such as over hunting and the destruction of habitats have become the main cause of extinctions today.