I was recently having a conversation with a friend of mine about transgender issues and transexuality, speicifically about the irrational fear and defensiveness that some people exhibit around gender-ambiguous folks. The conversation got me to thinking about Fear of the Other, Fear of the Unknown. I think I know why it exists.
Thomas Hobbes' Leviathan claims that government and civilization exist only to protect people from an often harsh world. Group evolutionary theory just might back him up on that.
Picture a small colony of mammals, pehaps lemurs (because lemurs are just cool). They eat, they mate, they fight, they get eaten. Perhaps one of the lemurs is unusually aggressive, interrupting courtship between mating pairs, raping females, and stealing food. (There's one in every group...) From a purely evolutionary perspective, this hurts the entire group. All the other lemurs have to spend more of their time and energy defending themselves, and are therefore less able to compete with other colonies.
Imagine that one colony has a tendency to punish unprovoked aggression, treating an aggressor as an outside attacker. With the aggressor out of the picture (dead or scared), the other lemurs can spend more time and energy on reproduction, food-gathering, and care of young, thereby outcompeting other colonies. Over time, the colonies with "laws" would tend to dominate the ecosystem.
Likewise, most of us feel safe enough to walk down the street without looking over our shoulders every few seconds, hoping to spot potential attackers. That's because our society strongly punishes physical aggression strongly, giving us time to concentrate on higher and more complex matters, such as long-term planning, strategic resource acquisition, and group efforts. Our highly developed industrial, legal, and social system gives us a framework upon which we can achieve great things.
But this system is predicated on enforcement of rules. If someone isn't following the rules, they aren't just taking advantage of the framework -- they are actively threatening its very existence.
(Not all rules are laws. There are also social norms, expectations, and conventions, some spoken, some unspoken. We call this collection of implicit rules the "status quo". Conservatives are those who promote and enforce the status quo, keeping society from degenerating into chaos and lawlessness. Liberals are those who agitate for change, pushing at the boundaries of what is expected, preventing society from falling into fatal stagnation. Both are necessary for a society that hopes to stand for long. A society must change itself in reflection of a changing world, but conserve certain aspects in order to prevent dissolution.)
When we encounter someone from our own society, we can assume they follow the same rules we do. When we meet someone from Outside, we don't have any such expectation. Who knows what their colony is like, what rules they might or might not have? The intricate network of give-and-take dissolves, leaving us feeling on-guard and unsure of what might happen next.
In other words, the Other, the Unknown, is (in our minds) a direct threat to the very foundation of our society. The Other does not follow your rules. Since it does not agree to the same principles and code of conduct, it is scary and unpredictable. The idea of communal suvival is predicated on a shared set of laws. That is why, even though they may be harmless, we are afraid of the Other.