Second, we measured the effects of natural selection by noting that women who were shorter and first gave birth when younger had more children. But genes are only one of many factors that influence height and age at first birth.
其二，我们发现了一种自然选择效应，那就是那些更矮而且更早生育的妇女将生育更多儿女。但基因只是众多影响身高和头胎生育年龄的因素之一。个人选择，营养水平，收入层次，教育和宗教状况等各方面因素会最终组合成一种混合性因素。