What is the best book I have read (so far) this year? It is a delightful question as we are fortunate to have so many smart people writing for us. So the question cannot be simple. Let me suggest, however, David Reich's Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past.
We humans (and others) carry an inherited tribalism. We learned to communicate and to form and sustain teams in order to survive -- and dominate the planet. Dunbar suggests that teams up to about 150 had worked best for our kind. Politicians and others conveniently muddle all this by harping on the idea that we all belong to one nation, one "community", etc. It Takes A Village. But be very careful about the extent of the village.
Demagogues understand all this and fuel convenient myths of tribal identity and origins. Exhibit A might be Hitler's peculiar stories about ancient and Aryan roots of the German "volk". It worked -- to make smart people very stupid and very nasty. But there are many others examples. Name a demagogue who does not follow a similar script.
Along comes David Reich who shows how modern DNA science strongly suggests that stories about "roots" are mainly bunk. The evidence shows that our ancestors were many, that they moved around a lot and that they bred promiscuously enough to challenge the idea of any simple genetic commonality.
There are, to be sure, cultural commonalities but they are not "blood" bonds. Which, then, are the better cultures? The ones that accept newcomers. Melting pot is still a great idea. Roots is a horrible and a dangerous idea.
Here is Arnold Kling re the Dunbar number.