Citation needed. In what culture "all females mate and carry the children of the one leader, all other males don't mate _at all, ever", or anything even close to this?
By contrast, there are a lot of cultures (eg. India, the Arab/Muslim world) where marriage is societally more or less obligatory.
This is still very new research, but not implausible. See for example section 3.6 in this paper [1].
> By contrast, there are a lot of cultures (eg. India, the Arab/Muslim world) where marriage is societally more or less obligatory.
An interpretation of that could be that it’s a result of memetics [2], i.e. several successful cultures have invented marriage because it makes them successful. Marriage might significantly increase social stability at all scales. For an interesting discussion about these kind of arguments from cultural evolution, see this blog article [3].
[1] http://arxiv.org/pdf/1203.6231.pdf
[2] https://en.wikipedia.org/wiki/Memetics
[3] http://slatestarcodex.com/2015/07/07/the-argument-from-cultu...
1. If all women mated with the same small group of genetically-gifted men, there would be much less gene-mixing and variation in their offspring. Not good for evolution.
2. Monogamy was invented because it takes a lot of time/effort to bring up human offspring (typically 18-21 years :-)). Mothers need a guarantee that fathers will be around to provide for the children.
2. As far as I know this is not fully known yet. It is conceivable that the offspring did just fine in polygamous relationships or just inside the secure environment that the pack provides. There is, for example, some evidence that intensive mothering is ineffective [1]. Among Great Apes the upbringing of the young is commonly shared between the members of the pack and the identity of the father is unknown. Moreover, consider that the importance of education only became really significant within the past 100-50 years, or so, but the concept of marriage in Western culture is much older than that [2].
[1] http://onlinelibrary.wiley.com/doi/10.1111/jomf.12170/abstra...