Bonobos compete for genetic dominance at the level of sperm. They are what we would call promiscuous, the females mate with multiple partners. He with the greatest volume of seamen and sperm washes out the competition. There's no need to be aggressive in person. Bonobo testicles are very large compared to, say, humans. Southern right whales are very similar in their mating habits. On the other hand, species where the male physically secures the females - elk, blue whales, humans, have much smaller testes and rely on physical ability to fend off other male challengers and secure their own genetic future. These traits were set in place long before "culture" developed. Culture is the result of these physical / genetic traits, not the cause.