Despite common concerns that the social is competitive, cooperation (合作) among strangers has gradually increased in the U.S. since the 1950s, according to the research published by the American Psychological Association.

“We were surprised by our findings that Americans became more cooperative over the last six decades because many people believe U.S. society is becoming less socially connected and less trusting,” said lead researcher Yu Kou, PhD, a professor of social psychology at Beijing Normal University.

The researchers analyzed 511 studies conducted in the United States between 1956 and 2017 with a total of more than 63,000 participants(参与者). Those studies included lab experiments measuring cooperation among strangers. The study found a small, gradual increase in cooperation across the 61-year period, which the researchers said may be linked to great changes in U.S. society. The increase in cooperation was related with increases in social wealth, income inequality and the number of people living alone.

Increased cooperation has been linked with market competitiveness and economic growth in former research. As more people live in cities and on their own, they may be forced to cooperate with strangers, said study co-author Paul Van Lange, PhD. He said, “U.S. society may have become more self-centered, but people have not.”

The researchers note that former studies have found that levels of cooperation do not differ by sex or race in the U.S. However, the studies were conducted in lab settings primarily with only college students as participants, so the findings may not be representative (代表性的) of real-life situations or of U.S. society as a whole.

Many of the present generation of recent over-18s do not feel like adults, according to a survey by Nationwide Building Society, and those commenting online seem to agree. The study of 2,000 over-18s found more than one in 10 did not think of themselves as fully-fledged (成熟的) grown-ups until they reached the age of 27.

Lisa Daisy, 34, said: “Even after a career for 10 years, it still took being married to make me feel grown-up.”

But 42-year-old Carole Lutringer said she felt like an adult when she was very young. “I had to cook from an early age, because my mother worked as a headteacher,” she said. “My mother came back home late, and my father was pretty useless in the kitchen. I had to be independent from really early on, and that’s probably what made me feel grown-up earlier than most of my peers (同龄人).”

Sana Khalid Khan also had adulthood thrust upon her. She said it was the death of her father that made her grow up, at the age of 17. “Being the eldest child, a lot of responsibility fell on my shoulders,” she said.

Of those 2,000 people asked when they felt like adults, the transition (转变) happened for half in their 20s, while a fifth said it happened in their 30s. One in 20 felt they had not grown up until their 40s. Of those questioned, 55% said being an adult was dependent on major life events, for example having children, moving out of the parental home or getting married.

For others, such as Elaine Smith, in London, adulthood is only a state of mind. “I still don’t feel grown-up,” she said. “I can’t believe I am responsible for looking after a four-year-old. How did that happen? I’m 44 this year, so it may happen soon.” Commenting online, Sophie Caunter agreed. “I’m 42,” she said. “I have an 11-year-old, a seven-month-old, a husband, and I still don’t feel grown-up.” Melinda Wilmot said, “I’m 58 and still waiting to grow up.”

Why do we find ugly animals so appealing? And what makes odd-looking creatures so cute?

Evolution plays a role. According to Austrian zoologist Konrad Lorenz, human attraction to infantile (婴儿的) features, such as big eyes, large heads and soft bodies, is an evolutionary adaptation that helps ensure that adults care for their offspring, guaranteeing the survival of their species. Odd-looking animals such as blobfish, pugs, aye-ayes and bulldogs all share these infantile qualities that trigger an affectionate response among humans and an natural instinct (本能) to nurture and protect. And these infantile characteristics increase a person’s protective behavior, attention and willingness to care for the individual and reduce the likelihood of aggression towards an infant, says Marta Borgi, a researcher.

Ugly animals often have other value-some, like the blobfish or the naked mole rat, live in extreme environments that they have adapted to in remarkable ways. Scientists are keen to study these animals to understand whether their biology might provide fresh insights that could lead to treatments for human health conditions such as cancer, heart disease and neurodegenerative diseases.

But while many ugly creatures are adapted to their life in the wild and can provide enormous benefits to the ecosystems they live in, they often still don’t get as much attention as more traditionally cute animals. This can result in a prejudice which leads to many of the less attractive species being overlooked in terms of research.

There are other culture-led factors that also drive our obsession (痴迷) with ugly-cute animals. “The ugly-cute thing is very fashionable,” says Rowena Packer, a lecturer of animal behavior. This is partly driven by social media, with many celebrities and influencers showing off pet pugs and French bulldogs on Instagram, she says.

But there are some serious welfare concerns around this trend. Veterinarians are urging people not to choose a flat-faced dog breed (品种), because they suffer from serious health problems. Pugs and French bulldogs which have been selectively bred experience breathing difficulties, repeated skin infections and eye diseases. So while ridiculous features such as bulging eyes and wrinkly faces may make us smile, we might want to reconsider our obsession with “ugly-cute” pets.