"The road to disaster is paved with pleasant illusions, and the way to deal with evil is not to ignore it," advised Abraham Joshua Heschel. 
The English philosopher Francis Bacon wasn't Jewish, but he said much the same thing: "Nature, to be commanded, must be obeyed." 
As Jews and people of goodwill, we want to "command" a goal that is both simple and seemingly impossible: A world of peace. An end to hatred and bloodshed. A cessation of injustice.
However, to have even partial success -- and partial success is the best we're going to get -- we must know what we're up against. What is the nature that we have to obey in order to command such a result? What are the facts we must overcome?
Someday, the Messiah might arrive and set everything right. Maybe he will change human nature. Until then, we're on our own. We have to try.
As of 2015, there were about 7.3 billion people on Planet Earth. There were about 20,000 different ethnic groups. There were about 20 major religious groups. Most of them dislike each other. Many of them hate each other and try to kill members of other groups whenever possible. This week's Palestinian terrorist attacks are only the latest tragic examples.
To say it's because of yetzer hara (the evil inclination) doesn't help much. That just means people do bad things because they want to do bad things. We need to know why they want it and why they think it's all right to act on that desire.
Three causes are most important: Kin selection, territoriality, and lack of empathy. Religious belief has an indirect role.
Kin selection is an evolutionary mechanism that makes us tend to trust, help, and cooperate with people whom we see as our genetic relatives. It also makes us tend to distrust and attack non-relatives who might compete with us and our families for food, living space, and mates. Biologists have observed kin selection behavior in animals as different as insects, birds, and mammals, including humans and lower primates.Of course, helping relatives and fighting non-relatives requires animals to know which are which. Animals (including humans, unconsciously) use appearance, behavior, familiarity, and location to identify their relatives.  They assume that if other animals look and act like them, they are relatives -- just as in humans, for example, Joe Junior looks and acts like his father, Joe Senior. If the others are already familiar or in the right location (such as a bird's nest, a synagogue, or a mosque), then it also activates the biological tendency to help and cooperate. In humans, it increases empathy toward the apparent relative.Encountering apparent non-relatives has the opposite effect: it activates the "fight or flight" response, preparing the animal to attack or run away. In humans, these responses occur at a biological level before they ever reach the conscious mind. They are the root of racism and other evils:
"When black and white Americans were flashed pictures of the other race, their amygdalas, the brain’s center of fear and anger, activated so quickly and subtly that the conscious centers of the brain were unaware of the response ..." 
The good news is that to varying degrees, learning and positive experiences can help about 84 percent of people override their fear-aggression responses:
"When contexts were added -- say, the black was a doctor and the white his patient -- two other sites of the brain integrated with the higher learning centers, the cingulate cortex and the dorsolateral preferential cortex, lit up, silencing input through the amygdala." 
From insects to humans, animals tend to view certain areas as their own. They fight non-relatives of the same species who stray into their territory. For example, male wasps attack other males in their territory and try to mate with females who enter. Chimp siblings form groups to patrol their group's territory, attacking and killing any alien chimps that intrude. Humans show the same kind of behavior:
"Territoriality became a defining characteristic of human behavior deep in prehistory, and the basic impulses to expand territory and power through team aggression have not diminished over the last 5,000 years ..." 
Hamas demonstrates both kin selection and territoriality:
"Hamas will never recognize the Israeli occupation, and confirms that Palestine from the Jordan River to the Mediterranean is an Arab, Islamic country ..." 
Note how the terrorist group talks in terms of "our" territory, "our" team, defined by ethnicity and religion.
(To be continued in Part 2.)
Heschel, A.J. (1955), The Insecurity of Freedom. Farrar, Straus and Giroux, New York. Kindle Edition.
Jardine, L. and Silverthorne, M., editors (2000), Francis Bacon: The New Organon. Cambridge University Press, Cambridge, UK.
Potts, M. and Hayden, T. (2010), Sex and War: How Biology Explains Warfare and Terrorism and Offers a Path to a Safer World. BenBella Books, Dallas, TX. Kindle Edition.
Slater, P. and Halliday, T. (1994), Behaviour and Evolution. Cambridge University Press, Cambridge, UK.
Wilson, E. (2012, The Social Conquest of Earth. Norton Publishing, New York.
1. Heschel, A.J. (1955), loc. 2098.
2. Jardine, L. (2000), p. 33.
3. Slater, P. and Halliday, T. (1994), p. 209.
4. Wilson, E. (2012), p. 61.
5. Ibid, p. 62.
6. Potts, M. and Hayden, T. (2010), P. 366.7. Braun, C., "On its anniversary, Hamas vows to 'keep its weapon directed at the Israeli occupation only," The Jerusalem Post, December 15, 2015.