It's definitely a necessity since there is not someone else there to help you with your kids.

VOA: standard.2009.12.04

If there's a group, responsibility to help decreases and this is captured in different ways but the main idea is we all think someone else will help so we don't. There's a diffusion.

如果是一群人，帮助的责任就会分散变小,这体现在多个方面,但最主要的想法就是我们都认为别人会帮助,所以我们就不帮助了，责任被分散了。

耶鲁公开课 - 心理学导论课程节选

Hence, selfish genes will lead to altruistic animals because, to the extent that evolution operates at the level of the genes, there's no hard and fast distinction between your own body and someone else's body.

所以，自私基因会导致利他行为，从这个意义上说,进化在基因层面进行，你自己的身体和别人的身体,没有严格差别。

耶鲁公开课 - 心理学导论课程节选

So it might look like here, if you don't understand about p orbitals, which I know all you do, but if someone else was just looking and seeing, it kind of looks like there's two bonds here.

这里看起来有点像，如果你们不知道p轨道的话，我知道你们都知道，但如果另外有个人看到这个，这看起来有点像两个键。

麻省理工公开课 - 化学原理课程节选