It may sound like a paradox, but a new theory suggests that one of humanity’s most noble instincts, altruism, evolved on bloody battlefields in prehistoric times. Evolutionary biologist Samuel Bowles argues that prehistoric culture may have selected for individuals who behaved altruistically towards other individuals in their social groups. The story begins with the climactic swings that occurred between approximately 10,000 to 150,000 years ago in the late Pleistocene period may have pushed once-isolated bands of hunter-gatherers into more frequent contact with one another…. “I think that’s just a recipe for high-level conflict” [New Scientist], says Bowles.
These conflicts weren’t large-scale pitched battles, Bowles explains. “We’re talking about groups of men who got out in twos or threes or fives,” he says. “They didn’t have a chain of command and it’s hard to see how they could force people to fight.” For this reason, altruistic intent on the part of each warrior is key. Each person would do better to stay home than to put their life on the line for their neighbours – yet they still went out and risked their lives, Bowles says [New Scientist].
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If aphids could recite Shakespeare, they might favor this rousing cry: “Once more unto the breach, dear friends, once more; or close the wall up with our [aphid] dead.” Researchers have discovered that the social insects send soldiers to repair holes in the plant tissue where they make their homes, and that some of the soldiers never return from these “suicide missions.”
Some aphids cause their plant hosts to form hollow swellings called galls within which the larvae mature. A hole in the gall’s wall threatens the larvae’s cozy and protected home, and causes soldier aphids to rush to the spot. There they excrete body fluids that represent about two-thirds of their body mass, and mix the fluids with their legs to form a scab that patches the hole. Many of the soldier aphids, of the species Nipponaphis monzeni, die from the significant loss of body mass. Many others get stuck in the viscous fluid and fail to escape. Like workers on the Great Wall of China, they simply become a physical part of the building work [BBC News].
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In a striking example of the evolutionary benefits of altruism, researchers have found a species of ants that sends a few workers out each evening on a suicide mission to ensure the continued survival of the colony. The tiny ant Forelius pusillus, which makes its home in sugar cane fields in Brazil, makes a nightly ritual of covering the entrance to its nest with sand. To be sure that the entrance is sealed shut tightly, a few ants remain outside each evening to finish kicking sand over the hole. Those ants, stuck outside in the cold and the wind, die during the night.
“In a colony with many thousands of workers, losing a few workers each evening to improve nest defense would be favored by natural selection,” said co-author Francis Ratnieks…. The ants stuck outside might be old or sick, [co-author Adam] Tofilski conjectured. Thus, they may have essentially sacrificed themselves for the greater good, being more expendable members of the colony [ScienceNOW Daily News].
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A new study has shown that salmonella bacteria use a surprising tactic when they attack a mammal’s intestinal system. A small percentage of the bacteria mount a kamikaze mission from which they’ll never return, but which helps allows the rest of the salmonella bacteria to thrive, spreading the infection and ultimately benefiting the species.
Researchers found that in the early stage of an infection, about 15 percent of the salmonella go on a suicide mission, invading the intestinal walls. There, the immune system handily wipes them out. But that also sets off a wider immune response that, while attacking the salmonella within the gut, also wipes out many other micro-organisms. “This inflammation removes many of the competitors, so the second group which waited outside can proliferate,” said [lead researcher] Martin Ackerman [The New York Times].
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