While I'm waiting for Fuckbot to process my question I'm going to explain in the simplest terms I can why a two-partner monogamous relationship is more evolutionarily advantageous than rape. Note that I'm speaking in evolutionary terms, so I'm assuming a hunter-gatherer lifestyle. I'm also not going to look at polygamy because I want to keep this simple.
Pros of Monogamy
- Easily able to care for up to two children at a time even in the absence of older siblings or relatives.
- Division of labor. One partner may gather food while the other cares for their offspring.
- No need to seek out new partners unless one spouse dies or leaves. All your reproductive options are right at your fingertips.
- Trust. You know you can trust your partner to be a good parent because you've had children with them before.
- Low risk of STDs.
- Lower risk of inbreeding because you know who your parents are.
- Males do not necessarily need to be physically strong to find partners as long as they have other attractive qualities or skills.
- Your mate will not only take care of your children but also take care of you, meaning that you will live longer and have more opportunities to reproduce.
Cons of Monogamy
- The female partner may cheat, resulting in offspring that do not pass on the male partner's genes. (Note that this is only a loss for the male being cheated upon. It may be quite advantageous for the female if her cheating partner has superior genes.)
- You have to earn your mate through your status in the tribe or by proving yourself somehow.
Pros of Rape
- Any female may bare your offspring, provided you can catch them.
- No social status required.
- Energy you would have used caring for your offspring can instead be used to sire more offspring.
Cons of Rape
- High risk of STDs from multiple partners.
- Higher risk of inbreeding.
- The male must be physically strong to restrain the woman and cunning to avoid being caught.
- If the female's mate catches you you will have to fight or flee. You can't pass on your genes if you're dead.
- The trauma of rape may kill or severely injure the woman, hindering her reproductive success.
- You will have less opportunities to reproduce because there will be fewer people looking out for you, if any.
- Your offspring may have only one parent to care for it.
- If the mother of your offspring already has a mate and he discovers the child isn't his he may kill it.
- The mother may be killed or exiled from her clan for having a child with a man other than her husband.
And that's just off the top of my head.