According to researchers, money can buy happiness, but only if you spend it on someone else.

Spending as little as $ 5 a day on someone else could significantly bring you happiness, the team at the University of British Columbia and Harvard Business School found.

Their experiments on more than 630 Americans showed they were measurably (适度地) happier when they spent money on others—even if they thought spending the money on themselves would make them happier.

“We wanted to test our theory that how people spend their money is at least as important as how much money they earn,” said Elizabeth Dunn, a psychologist at the University of British Columbia.

They asked their 600 volunteers first to rate their general happiness, report their annual income and detail their monthly spending including bills, gifts for themselves, gifts for others and donations to charity.

“Regardless of how much income each person made, those who spent money on others reported greater happiness, while those who spent more on themselves did not,” Dunn said in a statement.

Dunn’s team also surveyed 16 employees at a company in Boston before and after they received an annual profit-sharing bonus of between $3,000 and $8,000.

“Employees who devoted more of their bonus to pro-social (有益社会的) spending experienced greater happiness after receiving the bonus, and the manner in which they spent that bonus was a more important predictor of their happiness than the size of the bonus itself,” they wrote in their report, published in the journal Science.

They gave their volunteers $5 or $20 and half got clear instructions on how to spend it. Those who spent the money on someone or something else reported feeling happier about it.

“These findings suggest that very minor alterations in spending allocations (分配) -as little as $5—may be enough to produce real gains in happiness on a given day,” Dunn said.

A set of tusks (象牙) is usually an advantage for elephants, allowing them to dig for water, peel bark for food and defend themselves. But during episodes of intense ivory poaching, those big tusks may invite danger. Now researchers have figured out how years of civil war and poaching in Mozambique have led to a greater number of elephants that will never develop tusks.

During the conflict from 1977 to 1992, fighters on both sides killed elephants for ivory to finance war efforts. In the region, around 90% of the elephants were killed. The survivors were likely to share a key characteristic: half the females were naturally tuskless - they simply never developed tusks - while before the war, less than a fifth lacked tusks.

After the war, those tuskless surviving females passed on their genes with expected,as well as surprising, results. About half their daughters were tuskless. More confusing, two-thirds of their offspring (后代) were female. “The years of unrest changed the evolution in that population,” said evolutionary biologist Shane Staton.

Most people think of evolution as something that proceeds slowly, but humans can hit the accelerator. “When we think about natural selection,we think about it happening over hundreds, or thousands of years,” said Samuel Wasser, a conservation biologist at the University of Washington. “The fact that this dramatic selection for tusklessness happened over 15 years is one of the most astonishing findings.”

Now the scientists are studying what more tuskless elephants means for the species and its environment. “If an elephant doesn’t have the tool to peel bark from trees, then what chain reaction will happen?”

Some songs tend to get stuck in our heads more easily than others. When a song becomes super popular, we say it’s “gone viral”. Those words might be more accurate than we ever imagined.

David Earn is an applied mathematician. One day, he talked with musician and scientist Matt Woolhouse. Woolhouse found some songs had been downloaded thousands of times over just a few weeks or months. Those patterns looked familiar to Earn, who studies disease epidemics. And those download data resembled the kind of data he saw with disease transmission (传播). They wondered whether that kind of spread from person to person could be how people decide that they like particular songs.

Earn had been working with a mathematical model to predict how diseases spread during an epidemic. His team now used the same model with the song data. They looked at the 1,000 most downloaded songs in the United Kingdom, dividing them by type.

For popular songs, downloads increased rapidly over time, much like a contagious (传染性的) disease infecting a group of susceptible people. Some types were more contagious than others, the team reported in 2023. “The group of people who connect and like folk music isn’t the same as the group of people who like heavy metal or dance music. They’re different social groups,” Earn says. “And some of those social groups are much more likely to share things quickly.”

Surprisingly, pop music wasn’t the most contagious. It spread, but not as quickly as some other types. Electronic music, on the other hand, was super contagious. Earn thinks these listeners are probably super connected on the web and share things more than people who prefer other types of music.

“We think of contagion as a strictly negative thing,” Earn says. “But that same process of contagion functions for other things in life,” he now concludes, “like sharing favorite songs with your closest friends.”