Many things happen when people are ageing. Apart from the greying hair and wrinkled skin, there is a(n) 1 change which comes with older age. When humans reach their later years, they favour more long-term 2 and their social cirele is reduced.

Now, for what appears to be the first time, scientists have seen the same 3 in another species. Twenty years of observations of chimpanzees (猩猩) reveal that older males choose to keep contact with their 4 friends at the expense of other relationships.

The researchers studied 78,000 hours of observations made between 1996 and 2016 that followed the social 5 of 21 male chimpanzees between the ages of 15 and 58 years old. They classified the chimps' 6 depending on the amount of time they sat with others and groomed (梳毛) them. They then rated (分类) the various pairings as mutual (相互的) friendships, where both chimps seemed to enjoy the relationship;  7 friendships, where one chimp was more keen to be friends than the other; and non-friendships, where neither chimp showed 8 the other.

When the scientists looked at the 9 of friendships, they found that the older chimps had more mutual friendships and fewer one-sided friendships than younger chimps. Another 10 seen in older humans was also spotted in the chimps. As the males got older, their levels of 11 gradually become less, meaning they started fewer fights and tended to threaten others in their group less often.

The observations have left the researchers 12. According to an idea in psychology known as socio-emotional selectivity theory, older humans prefer more 13 relationships because they are aware that time is running out. However many animal experts argue that chimpanzees 14 the human sense of mortality (死亡) , suggesting something else is driving the behaviour.

Robin Dunbar, a professor of evolutionary psychology at the University of Oxford, said in humans, the 15 social circles with age is due to declining social motivation to get out and meet people combined by lack of opportunity. In chimpanzees, as older males compete less for mates, they may focus on close, reciprocal (互惠的) relationships with trusted partners, he said.

    Nipah, Hendra, Ebola, SARS... These are some of the world's scariest viruses, which are all carried by bats. This, to be clear, rally isn't bats' fault: The recent 1 . in outbreaks is likely due to humans and our animals 2 ever farther bats' habitat.

    In Malaysia, for example, the spread of commercial pig farms into bat-inhabited forests 3 the first human outbreak of Nipah via pigs. In Australia, human Hendra cases 4 as the destruction of native forests forced fruit bats to feed in suburban 5.

    One big reason is that most bats love 6 , which contributes to viruses spreading not just among individuals, but also among 7 species. What's more, most infected 8 don't die—they live normal bat lives, flying around and giving viruses the 9 to spread. Research suggests flight 10be the reason bats are so resilient (迅速恢复的) to infection.

    As a rule, when flying animals produce the 11amount of energy needed for flight, they also make a lot of reactive waste products that 12 their DNA. But when bats take to the air, they 13 their in-flight DNA damage repair ability and other defenses, including 14 cells that keep viral invaders in check.

So bats can 15 deadly viruses. But what may matter even more to humans is 16 viruses survive bats. When bats are flying, their body temperature can reach around 40℃. It's far too hot for the 17 viruses, but a few hardy viruses have 18 to tolerate the heat. This means they can definitely pull through a human 19when they are transmitted to humans, which is horrible to us.

    So what should we do? We'd better just leave bats 20.

    Making choices is hard. That would be why researcher Moran Cerf has 1it from his life. As a rule, he always chooses the second menu item at a restaurant.

    This is2by his research in neuroeconomics(神经经济学) (a somewhat new, divisive field) at Northwestern University. As Business Insider describes, Cerf has extended his ideas--which draw on some controversial ideas in psychology, including ego depletion out--into a piece of advice that, to 3 happiness, people should "build a life that requires 4 decisions by surrounding themselves with people who possess traits they prefer.

    On an instinctive level, Cerf's idea 5: Many choices people make are the product of social pressures and the inputs of 6 people around them. One example Cerf furnishes is that, 7 consistently ordering the second menu item, he never picks where to eat. Rather, he 8 his decision to his dining partner--which friend he plans to eat with, probably one he trusts--and always lets them pick.

    While it's 9 what, if any, scientific principles underlie those pieces of advice, there is no shortage of research showing that choices can sometimes feel more 10 than liberating. An example from Quanta poits (假设) : If you have a clear love of Snickers(士力架), choosing that over an Almond Joy(杏仁巧克力) or a Milky Way(牛奶巧克力) should be a 11. And, as an experiment conducted by neuroscientist Paul Glimcher at NYU shows, most of the time it is, 12 you introduce more choices. When the participants were offered three candy bars (Snickers, Milky Way, and Almond Joy) they had no problem picking their favorite, but when they were given the option of one among 20, including Snickers, they would sometimes drift away from their 13. When the choices were taken away in later trials, the participants would wonder what caused them to make such a bad decision.

    As Quanta details, according to a model called "divisive normalization(分裂归一化), which has gained some popularity, the way the brain encodes choices has a lot to do with how it values all its options. So, if you have two things that are clearly 14, brain areas involved in decision-making fire in a pattern that makes the decision clear. When the choices are comparable, the brain does its best to focus on the distinctions between the two, but more choices 15 that ability out.