science briefing

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Clive Cookson

Butterflies win bacterial warfare

Natural selection has enabled butterflies on neighbouring South Pacific islands to fight back with extraordinary speed against male-killing bacteria. Within 10 generations, the proportion of male "blue moon" butterflies on Upolu and Savaii in Samoa rose from 1.0 per cent to 40 per cent, as a protective gene spread through the population.
"To my knowledge, this is the fastest evolutionary change that has ever been observed," said Sylvain Charlat, lead author of the study, which was carried out by researchers at the University of California, Berkeley, and University College London and was published recently in the journal Science. "This study shows that when a population experiences very intense selective pressures, such as an extremely skewed sex ratio, evolution can happen very fast."
Wolbachia bacteria live in the cells of female blue moon butterflies and infect their eggs. Before these hatch, the bacteria selectively kill male embryos, which are useless for their own reproduction.
Fortunately for the butterfly, a "suppressor gene", which counteracts Wolbachia's effect, spread rapidly through the Samoan blue moon population between 2001 and 2006. The male-female ratio rose from 1-in-100 to 4-in-6.

Bad memories can be repressed

People can suppress emotionally distressing memories with practice, according to a study published recently in Science. The findings could help psychiatrists develop treatments for conditions such as post-traumatic stress disorder and depression.
Researchers at the University of Colorado measured brain activity in volunteers, who were asked actively to recall or repress the memory of disturbing images they were shown, such as a car crash, wounded soldier or violent crime scene. Subsequent tests confirmed that memories can indeed be suppressed with training.
Brain scans with functional MRI showed that two mechanisms in the prefrontal region of the brain worked sequentially in the volunteers to suppress memory. Subjects could "exert some control over their emotional memories", said Brendan Depue, lead author of the study.

Robot scales new heights

Engineers in Germany have developed a humanoid robot that can learn to climb up slopes without falling over. The bipedal machine, called RunBot, has an infrared eye to detect an uphill gradient and adjust its gait accordingly. Like a human walker, it leans forwards slightly and uses shorter steps.
Florentin Wörgötter and colleagues at the University of Göttingen describe RunBot's accomplishments in the latest issue of the on-line journal PLoS Computational Biology. At its first attempt to climb a ramp, RunBot fell over backwards, as it had not yet learned to react to its visual input with a change in gait. But just like a toddler, RunBot learned from its failures and could climb confidently after just a few attempts.
Although robots that walk and climb have been staples of science fiction for decades, they present great technical challenges. Late last year Asimo, the famous humanoid robot developed by Honda of Japan, suffered an embarrassing fall during a public demonstration of his ability to climb stairs. (FT Syndication Service)