"The main difficulty in refuting people who make the claim that "marriage" has "existed since the beginning of human history" for "men and women [to] come together...for the purposes of having children" is actually that there is too much historical fact that refutes it to easily summarize.
As an anthropologist, the temptation is to cite other cultures ...
But I think those responses, while valid, miss the point.
Santorum and others like him don't mean to include the practices of men and women in Native American, South East Asian, or African traditional societies when they say marriage has existed unchanged since "human history" began, and they don't care if primate studies suggest our species might not actually be quite so naturally straight as they imagine. They mean the history that they claim as their own: the one sanctioned by God as continuing "civilization".
But they are still wrong about those historical facts."
And I'll also quote the last sentence, which is I think the real take-away from the article:
It is inhumane as well as ahistorical, and it ignores the one real universal about our species: we are human, and humans evolve to fit their times and circumstances.
Original blog post here
Interesting meta about writing such a post is here