A pessimistic view of human nature argues that when times are bad, and they cannot migrate out of the situation, or fix it technologically, humans have a predisposition to lay blame on foreigners, and come to believe that the strangers ought be killed.
This view suggests that powerful contemporary societies in which people see themselves as losers, will become more and more xenophobic. This is an explanation both for some Moslem actions against the US and for the US response: in both societies, many perceive their hopes as different from what they expect. Times are perceived as bad.
The view expresses the old Christian belief that `Man is Fallen'; that there is an intrinsically evil capability in humans. The view is in opposition to the more recent belief that humans are perfectible.
I do not think the existence of an intrinsically evil capability means that you must act on that capability. That is a matter I consider briefly further down.
First, a suggestion as to how this capability came to be.
The fundamental thesis is that groups of our stone age ancestors developed this capability as an aid to survival.
Every so often in the Paleolithic, a long-lasting drought or glacier would come. Or the population would increase, whether local or neighboring. In any event, the environment would change.
A primitive people had four alternatives in such situations:
The Americas were, for a period, a gloriously large and unsettled territory. The islands of the Pacific were also empty at first. They could be and were settled by hardy, long range Polynesian migrants.
Only later did the Pacific islands fill up, so that new explorers came upon inhabited islands, and, often enough, got killed by the locals, who did not want more mouths. (Even later, Europeans came; but they had bigger ships, so they could carry more for trade, and more advanced technologies, so they could protect themselves, more or less. Even so, two famous European explorers, Magellan and Cook, were killed by islanders.)
Those groups that permitted a portion of their population to starve became weaker. They did not reproduce so much as others, and failed to pass on their genes and their cultures as strongly as others.
A favored solution in the United States is to invent new technology. This is my personally favored solution. I think we as humans are now in different circumstances than before. But invention was not always possible.
Migration is possible under either of two conditions:
This enabler did not exist when every hunter-gather band enjoyed about the same level of technology and the same immunities.
Without a possible technological fix, without empty land, a group that faces catastrophe sees one and only one option: to fight and kill their neighbors. Or else to die themselves. (Not all need anticipate death; only that enough die that it be foreseen as a disaster.)
The choice comes to be seen as between death for oneself and death for one's neighbor.
Under such circumstances, a group is more likely to succeed in killing its neighbors if it does three things:
Keith Henson, on a mailing list, suggested xenophobia. He says his inspiration for the notion comes from evolutionary psychology. The need for more savy leaders and for at least some people who will gather information on strangers comes from me.
(I do not know whether evolutionary psychology provides a good explanation. It did provide a good source of the hypothesis. As for an explanation, you can easily point out that surviving groups would pass on genes or culture and that dead ones would not; but that does not tell you whether the characteristics became more inherited as specific modules of mind or culture, or as a more general feature of increasing human adaptiveness. In any event, for my current purposes, that is neither here nor there.)
Henson also suggested that
... war may be highly non-adaptive for technologies higher than hunter gatherer. For example, warfare in the American Southwest starting about 1250 CE and the response the tribes made (moving into forts) was incompatible with their corn farming technology. This incompatibility caused continuing privation driven war. The result was that most of the population died out in a generation.
(See Rebecca Hill's book review of Stephen A. Leblanc's Prehistoric Warfare in the American Southwest in Athena Review, Vol.2, no.4. The book was published in 1999 by the University of Utah Press, ISBN 0-87480-581-3.)
Henson's example is controversial; some think there was not so much prehistoric warfare in the American Southwest. But more significantly, his thesis may be wrong as it applies to more modern people. Xenophobia may not be non-adaptive among technologically advanced groups.
First, a good many groups that are more technologically advanced than their competitors have killed off their competitors and taken over their land. Think of Tasmania; most of the previous inhabitants are gone; it has been settled by a new and different people.
Second, xenophobia may be avoidable.
Either way, regardless whether xenophobia is or is not adaptive in the modern world, Henson is right in arguing that it exists. (And along with xenophobia, there exists, I think, a desire for savy leaders and for spies, at least in times of trouble.)
Put another way, a pessimistic view of human nature is merited. You cannot argue the optimistic view that humans are perfectible.
But in practice, a different question is more salient than whether humans are perfectible or fallen: the salient question is not whether xenophobia is avoidable? It is whether we humans must always act badly, as groups if not as individuals?
Can human limitations be overcome by good governance? Can institutions be created to discourage xenophobia and encourage xenophilia?
After all, in the modern world, we are talking about capabilities, not necessities.
Much more than any previous generation of humans, we have the option of technological fixes. We can grow more food; we can limit human populations in less dangerous ways than before; we can live comfortably with less use of a fixed stores of energy, such as that in oil reserves, and with more use of alternatives.
We can migrate, as many science fiction writers have suggested, to places uninhabited by humans.