There’s some disagreement about how long modern humans have existed but the figure of 200,000 years is frequently cited. The lifestyle of the stone age was wandering groups of associated families usually between 25 to 50 people. Pretty much anyone you knew, you knew for a lifetime (yours or theirs). The stone age ended as the neolithic revolution in farming transformed the lifestyle of people into the sort of population dense settlements that have basically carried on to this day.

The Population Reference Bureau estimates that about 107 billion people have ever lived – since the beginning. Scientists suggest that out of that huge number, only about 12% of those people lived in the stone age. 12% doesn’t sound like a very significant number to influence the sort of people we are today. Until you realize that every person since then is a descendent of that 12%. And even more importantly that that 12% of all people was us during 96% of our time on Earth. Our roots are deep, deep in the stone age. 

So our inner cave clan easily breaks through the surface of our modernism. 192,000 years of comforting small groups of closely related people with a distrust of strangers is not something you shake off like a daydream. When we utterly detest racists and xenophobes we are behaving toward ourselves as we might to our dog humping legs at a party or chewing shoes. We shout “NO!” and we drag them off, “stupid dog” we mutter. The dog’s behavior has been momentarily suppressed but not altered in the slightest. And certainly not for the next generation of dogs. 

Picture those stone age ancestors suddenly trying to absorb a group of outsiders with radically different ways.  You have in a nutshell, the reaction of people all over the world today to an influx of outsiders. Suspicion, fear, concern for the end of the comfortable and familiar OURSELVES: Fear of family closeness and relatedness being diluted. All species have comfort borders of insider and outsider, self vs not-self. An influx of outsiders causes a sudden heated policing of those borders.

We are in the position of adapting to extraordinary and rapid changes in our comfort zones . But simply name calling people who are acting like people always have, and summarizing them as stupid for doing so is not a real answer. It also shows a lack of recognition for the extent of the problem. This iceberg goes a long way below the surface. 

There is probably no chronically intractable problem of the human race that wouldn’t be better understood with a common-sense, humble and humane use of an evolutionary perspective. Claim your mammal nature, it’s warm and fuzzy in here.