Every culture on the planet has an origin story, a way they describe how things came from not-being to being. In this, they often have a mythic narrative that also discusses how the first man and woman came into existence.
Equally as often these progenitors are presumed to be just like us. If you were to transport the First Ones through time, they might be surprised by the use of modern tools or new cultural taboos but they would still fundamentally be recognizable to us and even, over time, become acceptable (even revered!) in our modern culture.
For almost 1,800 years, the dominant narrative has been of only two people—an Adam and an Eve—instead of a first tribe or a pair of couples or a set of hermaphrodites separated by the gods. This formed a very distinct starting point. Before Adam & Eve, there was nothing like them and after them, nothing different was ever conceived (at least by the gods).
A mere two-hundred years ago, Charles Darwin was wandering the world and observing things (and just as often meddling with them). In contrast to the prevailing thought at the time (”God made everything. Deal with it”), he discovered that life exists as a series of discrete relationships that can change slowly over time. It wasn’t the first time folks had noticed it, but its presentation was well-timed and shook up the world at the time.
Much to Darwin’s horror, a number of people (including members of his family), choose to focus on the ‘discrete’ instead of the ‘relationship’ part of his theory. From this particularly loathsome attention came the fields of eugenics and genetic determinism. Now, people had a ‘scientific’ way to justify prejudices. Poor people? Poor genes. Criminal tendencies? Must have passed from father to son. The god-blessed positions of royalty and their sycophants? Now blessed by Reason.