Animals from temperate regions reserve sexual activities to the late winter/early spring period every year, so that there is plenty of food and energy for the gestating female and the young offspring, as well as there being plenty of food (numbers and other species) for the hunters of the ecology. They also tend to migrate a fair bit, for food and water supplies. Animals from tropical regions have an all year round supply of food, so tend, like the plants, to breed all year round. They do not need to migrate so much as they have all they need.
From this we can deduce that humans must have evolved primarily in tropical regions, as they tend to breed, or copulate, any time of the year. However, it is common to see a lot of people coupling up in spring, and less so in winter (more often break ups), so temperate influences must have effected our evolution, but it is definitely secondary in it's influence.
Also, being monogamous seems to be the vast majorities presumption, although most do not remain in the same monogamous relationship for life. Pairing permanently seems fairly rare when choice is involved. Serial monogamy, with one or two being very long term, is the most common "how it turns out". Polygamy seems rare, and temporary, whether the person(s) are male or female. Usually if more then two are involved in a romantic relationship, there is tensions involved with the truth being denied. However, some rare folk manage different systems by pragmatic and mature methods, using honesty and sensibility.
Status, like most animals, seems to effect behaviour in the mating habits of people.
Also, in the animal world, sexual activity, promiscuity and time spent rutting, determines the shape and size of their groins. If they mate for life, such as birds, they tend to have small penises and don't spend much time in the act. They don't need to, because procreation is mostly guaranteed once they have a mate. They spend more energy looking pretty, clever, good at nesting and/or tough to win the female in the beginning.
However, if the female is promiscuous, having either many partners in one impregnation, such as insects, or changes partners seasonally, the males get bigger penises, spend more time in the act, and get fancy adaptions (like spores or knobs or the ability to leave his severed penis in the vagina) in the groin. This is because he is not guaranteed to be the father, so he has to outdo his rivals. You can interpret that as you wish when you consider human sexuality, female and male behaviour, and the size of the male penis and their staying power. Amusing, isn't it?