Joseph Giovannoli

Is Polarization Genetic? explains why the United States has become increasingly divided on social and political issues since the 1970s. This third book in a trilogy explains why contrasting liberal and conservative psychological traits evolved as an advantage that gave Stone Age ancestral groups more options for solving problems and competing with other groups. However, an environmental change at the end of the last ice age diminished member collaboration.
Without collaboration, once-beneficial differences in members' conservative and liberal perspectives polarized members into factions, each blind to the wisdom of the other. And to varying degrees, we inherited their liberal and conservative genetic traits.