The term pygmy usually refers to a few groups of short-statured people in equatorial rain forest regions in Africa. The existence of distinct populations 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 500 members of a west African ethnic group called the Baka. They discovered that Baka infants have a similar size range to most other infants, but have a low growth rate during their first two years, which produces a lasting effect. This mechanism seems to be different from that of the east African groups called the Efé and Sua. These peoples have slow prenatal growth, so that the infants are born smaller. The researchers say that the Baka population appears to have split from the Efé and Sua some 20,000 years ago.