Weirdness cannot be defined, but whatever it is, it evolved, which means it provided an evolutionary advantage at many times during human evolution.
One reason it cannot be defined is that what one culture, in space or time, considers weird, another culture may not. One example is psychopaths. In most cultures, most people dislike psychopaths. They are very, very smart, and almost always use their intelligence and their charisma to advance their own interests. We tend to think of the psychopathic mass murderers and other criminals, but many psychopaths (who constitute about one percent of the population) pass as ordinary people and may be surprised by their own (often genetically-based) diagnosis. A lot of politicians and preachers are psychopaths, who cultivate the goodwill of others for their own financial or sexual benefits. And they also like to shame you for suspecting that they are committing acts of evil. It takes highly-developed social intelligence to recognize a psychopath. See the book by Kevin Dutton: The Wisdom of Psychopaths: What Saints, Spies, and Serial Killers Can Teach Us about Success. New York: FSG, 2012.
The success of psychopaths depends on the social situation. Adolf Hitler was a psychopath, and he got millions of people to follow him. After Germany lost World War Two, many Germans felt mentally liberated, and wondered, What were we thinking, to follow this jerk? Germany was not a nation of psychopaths, but maybe the Nazis were a party of psychopaths.
But there are many other ways of being weird. Most of us are a little weird in a few ways. But I mean clinical weirdness. One example is Williams Syndrome [https://en.wikipedia.org/wiki/Williams_syndrome]. People with Williams Syndrome have distinctive facial characteristics, and medical problems such as heart conditions. They have diminished intelligence, overall. They are extremely talkative, and effusively express their emotions. They are almost always cheerful. I have never knowingly met one but I get the impression that it would be really hard to not like them.
One word you would not associate with Williams Syndrome is suspicious. In order to become socially powerful, within your society, you have to be suspicious of the motives of other people in your society, and certainly of people in other societies. People with Williams Syndrome will walk right up to you and trust you. This is socially awkward. But openness and the willingness to trust is an essential component of altruism, of social bonding. It’s just that these people have too much of a good thing.
Another reason weirdness cannot be defined is that each kind of weirdness has its own social and genetic basis. Williams Syndrome is associated with a specific genetic deletion that affects a specific part of the brain. There is no set of terms in any language that exactly matches the symptoms of this deletion. And, in fact, characteristics resulting from mutations can be highly modified by upbringing and social circumstances. I am thinking of a person who acts as if she has Williams Syndrome, but who looks normal, and is brilliant.
Throughout human evolution, behavior patterns have sometimes been useful and sometimes not. Since each behavior has a different set of causes, human behavior has proven to be immensely variable. This has happened not because natural selection has done a bad job on human behavior, but because both the source and the target of human behavior is constantly shifting.
We can be glad we have empathy and altruism in the human species. And maybe Williams Syndrome is the price we pay for it.
Next, I will write about the evolution of nerds. Or not. Maybe I am a bit too close to the subject to be objective.
