[科学美国人60秒] SSS 2015-08-03（在线收听）

 The term "Pigmy" usually refers to a few groups of short statured people in equatorial rain-forest regions in  Africa. The existence of  distinct population of such people presented scientists with the opportunity to study the mechanisms by which typical human growth patterns have become altered there. And they discovered that two groups became small in two different ways. The study is in the journal " Nature Communications." The researchers collected data on some five hundred members of a west  African  ethnic group  called " The Barka." They discovered Barka infants have a similar size range to most of the other infants, but have a low growth rate during the first two years which produces a lasting effect. This mechanism seems to be different from that of east African group called " the Effa and Sua." These peoples have slow prenatal growth so that their infants are born smaller. Researchers say the Barka population appears to have split from  the Effa and Sua some twenty thousand years ago. The two systems for achieving smaller stature which appears to be advantageous in equatorial rain forest environment are thus an example of conversion diversion. The researchers believe the finding say something important about human evolution and development in general, " homo sapiens could therefore be characterized by its high capacity for growth plasticity during infancy. This capacity, which may be unique to our species, may have played a fundamental role in the biological adaptation that enabled its worldwide expansion and occupation of dissimilar environment within a short period after moving out of Africa.