One theory is that bipedality evolved in conjunction with the nuclear family: monogamous parents cooperating to care for their offspring.
有一种理论认为，两足动物的进化与核心家庭有关：一夫一妻制的父母合作照顾他们的后代。
2
Bipedality made a big difference in a hostile and unforgiving world.
在一个敌对而无情的世界里，能否用两足行走有很大的区别。
3
If it turns out that the big two - bipedality and nakedness - arose at roughly the same time, that might shift the balance of probability some little way toward Hardy.