Final answer:
The evolutionary instinct that explains why we are safest when we can predict the behavior of others is 'tribalism.' This instinct stems from our need for survival, which is supported by forming allegiances with in-groups and the fact that human behavior, to some extent, is predictable.
Step-by-step explanation:
We are safest when we can predict the behavior of others. This explains our evolutionary instinct of tribalism. Tribalism is an evolutionary advantage for social creatures like human beings, and it is ingrained in our behavior due to both sociobiology and evolutionary biology, which attempt to explain all behavior in physical terms. Through tribalism, we form groups to share knowledge and distribute work, increasing our chances of survival. Pro-social behaviors lead to higher persistence rates in the population compared to antisocial tendencies.
However, while predictable behavior is observed and can allow us to make good guesses about people's actions under specific sets of rules and conditions, behaviors are not entirely random nor exactly the same for every individual. There are innate tendencies within our species that rear themselves in social behaviors that seek approval from in-groups, which can be influenced by environmental factors and cultural pressures.
Despite the uniqueness of each individual, humans have been forming groups and creating predictable social patterns throughout history. This enables us to see outsiders, sometimes with suspicion, and form allegiances within our groups, thus reinforcing our evolutionary instinct to predict the behavioral patterns of others for safety and cooperation.