Health & Science

The evolutionary roots of monogamy

As an evolutionary strategy, monogamy has long puzzled scientists: When a male pairs off for life with one female, he limits how many offspring he can produce, thus reducing his chances to pass on his genes. Few species are monogamous, yet 5 percent of mammal species are, including wolves and beavers—and about a quarter of primates. To find out why, British scientists gathered data on the mating behaviors of 230 primate species, and used computer simulations to analyze how they evolved. Their conclusion: Males began sticking around their mates to prevent other males from killing their offspring. When unrelated males have access to females with babies, the study found, they tend to get rid of the babies because it ends the suckling period and makes the moms fertile again. “Infanticide is a real problem, particularly for social species,” anthropologist Christopher Opie tells The Washington Post. By coincidence, a separate group of researchers just completed their own study on monogamy, and they came to a different conclusion. Pair-bonding evolved, they say, when females of some species began living away from other females, spreading out to get more food. Males had to “move in” with them to fight off other suitors and preserve their sexual access. Tim Clutton-Brock, an evolutionary biologist at the University of Cambridge, cautioned against applying these studies to modern humans—especially given how humans behave. “I’m far from convinced that humans are really monogamous,’’ he said.

Manufacturing memories

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Memory is notoriously unreliable: Eyewitnesses have sent innocent people to jail, and two people can give conflicting accounts about the same event. In a new study, The New York Times reports, MIT researchers have shown how false memories can form—and how they might even be implanted. The researchers placed mice in an unfamiliar box and used chemical tags to mark the cells in the hippocampus portion of their brains that became active as a memory of their surroundings formed. Then, they transferred them to a different box and gave them an uncomfortable electric shock while stimulating the brain cells they’d marked in the first box. When they finally returned the mice to the original, harmless box, the rodents stiffened in fear—suggesting that they remembered, wrongly, that it was where they’d been shocked. The mice didn’t feel frightened when transferred to other new boxes, showing they had a specific false memory attached to the original box. Human brains likely encode memories in a similar way, and the research should “make people realize even more than before how unreliable human memory is,” says study author Susumu Tonegawa.

How ‘stop-and-frisk’ backfires

Young people who are randomly stopped for questioning by the police—even if they’ve done nothing wrong—are more likely to engage in criminal behavior later than those who aren’t stopped, a new study has found. University of Missouri researchers say that “stop-and-frisk” programs intended to deter crime may actually create more criminals. Researchers followed 2,600 students for seven years and recorded who was searched by the police, who wasn’t, and who was arrested. They found that, on average, those who had contact with the police early on committed five more delinquent acts—like skipping class, selling drugs, and assault—than those who hadn’t, regardless of whether or not they’d had a history of behavior problems when they were first detained. Demeaning encounters with police also made students less likely to say they would feel guilty about committing a crime in the future and more likely to make excuses for bad behavior. “The theory is that when you’re publicly labeled as delinquent, you start to take on that role,” study author Stephanie Wiley tells Time.com. Positive interactions with police officers, on the other hand, appear to make young people more likely to obey the law.

An effective diet strategy

The key to losing weight and staying slim may be dieting—for only two days a week. A growing body of research suggests that “5-2” diets—which involve eating normally for five days and restricting your intake for two days to between 500 and 1,000 calories—are effective both in keeping weight off and in improving overall health. In a study on rats, researchers at the National Institute on Aging say the periodic fasting appears to improve the blood sugar levels of the rodents and help keep them lean, NPR.org reports. It even appears to boost their cognitive skills. And a study of 100 overweight women in England found that those who followed a 5-2 diet—eating healthy Mediterranean-style meals for five days and low-calorie, high-protein meals without carbohydrates for two days—lost more weight than women who tried to cut calories all week. The big advantage of two-day diets, researchers say, is that they seem to train people to eat less overall without making them feel deprived.