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。
One theory is that bipedality evolved in conjunction with the nuclear family: monogamous parents cooperating to care for their offspring.
和研究人员怀疑的一样,在其他条件相同的情况下,一夫一妻制的家庭育有更多的儿子:平均每生出100个女儿,就会生出101个儿子。
As the researchers suspected, when all other things were equal mothers in monogamous marriages had most sons: 101 for every 100 daughters.
这些等级较低的妻子与地位较高的妻子或一夫一妻制家庭的妻子相比,生的女孩更多。
These low-ranking wives have relatively more daughters than higher-ranking and monogamously married wives.
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