This is from Quora: How can you tell if someone has a high IQ? The answer was supplied by Bruno Campello de Souza, Professor at Federal University of Pernambuco. He sensibly shied away from identifying high intelligence with high IQ. Although they may be related, they are not the same. This was his answer.

There are observable signs of intelligence that tend to be more easily spotted by those with higher IQ than by those with lower ones. The saying below may sound obnoxiously elitist, but it does seem to hold:

Mediocrity knows nothing higher than itself, but talent instantly recognizes genius. – Sir Arthur Conan Doyle

Having said that, in no particular order, the signs that one is interacting with a person that has a very high level of intelligence include perceiving in that person:

• An appetite for information and knowledge, which includes not only curiosity, but also a veritable “need” for intellectual stimulation;
• The ability to quickly understand your arguments without the need for much explanation, perhaps even anticipating the final conclusion before you get to it;
• Identifying interesting implications and consequences of your arguments that you yourself had not considered;
• Displays of rapid perception, strong learning capacity, and substantial problem-solving abilities;
• A broad scope and/or depth of knowledge;
• The ability to perceive and appreciate the relevant talents and accomplishments of others.

When you see most of these signs in someone, you can tell that they are an intellectual “force to be reckoned with”.

The comments that follow his post are also worth a look. There is also this further posting by Professor Campello de Souza: Are more intelligent people more likely to be alone. The post begins:

In a study with 1,383 adults from Pernambuco, Brazil, IQ was negatively associated to both Extraversion and Agreeableness.

He speculates that the following characteristics may be in play.

• With a higher IQ, there is a tendency for a higher level of working memory and also long-term recall, as well as speed of processing, which grants the ability to generate more and better mental imagery, thereby creating an incentive for “daydreaming” or “zoning out” (think of having your own personal “mental holodeck”);
• IQ is, by definition, the capacity to deal with abstract thinking, making the intellectually gifted more prone to detach from concrete experiences;
• The things that many of the Gifted are most interested in are not the things that attract the vast majority of people, the same happening with their life and work experiences, so that the highly intelligent may not find much in common with the majority of people and vice-versa;
• Being a minority by definition, a relevant portion of the Gifted might be the object of prejudice, making them more prone to withdrawing from social interactions and/or being less inclined to be less empathetic or altruistic;
• The differences in the size and breadth of vocabulary between the Gifted and most people might make communication more difficult or cumbersome;
• The Gifted can, at times, become frustrated, impatient or irritated with the slower and/or more limited intelligence of normal individuals, something which can come from elitism, self-importance, sense of superiority and even Narcissism, but can also arise from honest exhaustion from continuously having to wait for, explain to, correct, and accept errors from most of the people one interacts with.