Science and Medicine

Sports Stats Show Why Lefties are Rare

Cooperation favors same-handedness—for sharing the same tools, for example.

Left-handed people are relatively rare because of the balance between cooperation and competition in human evolution, according to a new study of sports data.

Representing only 10 percent of the general human population, left-handers have been viewed with suspicion and persecuted across history. The word “sinister” even derives from “left or left-hand.”

Researchers at Northwestern University now report that a high degree of cooperation, not something odd or sinister, plays a key role in the rarity of left-handedness.

They developed a mathematical model that shows the low percentage of lefties is a result of the balance between cooperation and competition in human evolution.

Professor Daniel M. Abrams and graduate student Mark J. Panaggio—both right-handers—are the first to use real-world data (from competitive sports) to test and confirm the hypothesis that social behavior is related to population-level handedness.

The results are published this week in the Journal of the Royal Society Interface.

“The more social the animal—where cooperation is highly valued—the more the general population will trend toward one side,” said Abrams, an assistant professor of engineering sciences and applied mathematics at the McCormick School of Engineering and Applied Science. “The most important factor for an efficient society is a high degree of cooperation. In humans, this has resulted in a right-handed majority.”

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Depressed Moms Disrupt Babies’ Sleep

“One has to examine the health of the family system and address the problem at that level.”

Women who are depressed are more likely than other mothers to needlessly wake their babies from a sound sleep out of worry.

“We found that mothers with high depressive symptom levels are more likely to excessively worry about their infants at night than mothers with low symptom levels, and that such mothers were more likely to seek out their babies at night and spend more time with their infants than mothers with low symptom levels,” said Douglas M. Teti, professor of human development, psychology, and pediatrics and associate director of the Social Science Research Institute at Penn State.

“This in turn is linked to increased night waking in the infants of depressed mothers, compared to the infants of non-depressed mothers,” Teti said. “Especially interesting about this was that when depressed mothers sought out their infants at night, their infants did not appear to be in need of parental help. They were either sound asleep or perhaps awake, but not distressed.”

In contrast, mothers with low levels of worry and depressive symptoms rarely wake their infants out of a sound sleep and hardly went to their infants at night unless the infants were distressed.

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Fasting for Lent Forces Hyenas to Change Diet

Ecologists have discovered these changes in human diet have a dramatic impact on the diet of wild animals

Many Christians give up certain foods for Lent but ecologists have discovered these changes in human diet have a dramatic impact on the diet of wild animals. In Ethiopia, members of the Orthodox Tewahedo Church stop eating meat and dairy products during a 55-day fast before Easter. As a result, spotted hyenas too change their eating habits—from scavenging waste from butchers and households to hunting—new research in the British Ecological Society’s Journal of Animal Ecology has found.

Spotted hyenas are supremely adaptable mammals, capable both of adapting to habitats with dense human populations and to eating whatever food is available. While they are efficient hunters, they are also opportunistic scavengers, eating everything from birds, mammals, fish and reptiles to garbage, cooked porridge and dung. And they have digestive systems to match, says Gidey Yirga from Mekelle University.

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