Today, about one-tenth of the world’s population are southpaws. Why are such a small proportion of people left-handed -and why does the trait exist in the first place? Daniel M. Abrams investigates how the uneven ratio of lefties and righties gives insight into a balance between competitive and cooperative pressures on human evolution.

今天，世界上大约十分之一的人口是南撇子。为什么有这么小比例的人是左撇子--以及为什么这种特征首先存在？丹尼尔-M-艾布拉姆斯（Daniel M. Abrams）研究了左撇子和右撇子的比例不均如何让人了解到人类进化过程中竞争和合作压力之间的平衡。