In THEIR menacing black helmets and commando-style boots, the Moscow bailiffs look like an occupation forcespreading fear and destruction along the Banks of the Moskva river.
Although the likelihood of any neutral mutation spreading by chance is tiny, the enormous number of mutations in each generation makes genetic drift a significant force.
虽然任何中立变异随机传播的可能性很小，每一代个体产生的大量变异却使基因漂变具备显著的力量。
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But malnutrition 'is a driving force in emerging infectious diseases that are spreading around the world, ' she says.