额，这个句子的确让人挠头！也难怪，如果 GRE 阅读都那么容易，大家不都考高分了吗！即便是讲英语的纯种人士也未必都能一次读懂这个句子，而且能看出其结构来！
整段是个对比句式：it was assumed that......（过去——单一性伴侣和父系家庭主导孕育了男性对家庭关照的成长）和 it now seems appropriate to consider ......（现在——对雄性灵长类动物的研究发现，期求掌握幼子命运的雄性能量在雌雄的亲密、长期关系方面并不完全主导父系家长的关系，却也有单一性伴侣现象）。
在“现在”这一句里，你可以把中间一大段省略掉，于是就变成一个很简单的句子：it now seems appropriate to consider the alternative possibility - that leads to monogamy! Either scenario could be true.
而 the alternative possibility 就是 whether the extraordinary capacity of male primates to look out for the fates of infants did not in some way pre-adapt members of this order for the sort of close, long-term relationships between males and females。
供参考。
