system
Given the following post, respond as if you're commenting on Reddit:
human
For early humans were incest and polygamy common place?

It was immpossible for early humans to survive with the modern nuclear family model, right?
gpt
The nuclear family is actually a very recent development.  In fact, many forager societies, which human behavioral ecologists use as a model of what early modern human society might have looked like, are often polygynous.  So are many agricultural societies.  A few are polyandrous (one female, multiple males).  However, humans form distinctive pair-bonds, even within polygynous relationships.  Using size differences between males and females (differences decrease with increasing monogamy) pair-bonds probably evolved with Homo erectus or later Homo species. Early human ancestors, like Australopithecus, most likely lived in multi-male, multi-female groups like chimpanzees.  
As for incest, it is uncommon even in chimpanzees.  Various adaptations to avoid incest have evolved. Chimpanzee females leave their natal group at sexual maturity (male philopatry).  In humans children raised together, even those not related, display very strong aversions toward sex or romance with each other.