The Endogenous Personality refers to someone who is inner-orientated: inner-directed, inner-driven, inner-motivated; one who uses inner modes of thinking, inner evaluations; one who is to a high degree autonomous, self-sufficient; one who is relatively indifferent to social pressures, influences and inducements.
The suggestion is that this personality complex is associated with genuine creativity and - in rare instances, with creative genius.
But how can you tell if someone has the Endogenous personality type, rather than just being socially-impaired for some reason?
The Endogenous person has a strong inner motivation. He does not avoid groups and social responsibilities simply from lack of interest, because he wants to do nothing; but because hewants to 'do his own thing', because he is powerfully interested in some thing, driven to do something. His mind is often full with plans and aims and aspirations.
These may or may come come to fruition - some people with an Endogenous personality are late-developers, and may superficially seem to be adrift, or to change direction too frequently to become successful; but they are actually trying to find their subject, trying to find their destiny.
For example Francis Crick started and gave-up two PhDs, and worked on naval research before he found what he 'should' have been doing in his mid-thirties, and co-discovered the structure of DNA.
The Endogenous personality has high intelligence. This may be apparent through good exam results in a 'g'-loaded evaluation - but may require formal intelligence testing to detect, if the individual has either suffered from poor or absent education, or else has lacks the conscientiousness to apply himself to studies.
High intelligence is a sign of having an overall efficient, fast-processing brain - with (as Geoffrey Miller has pointed-out) a minimal load of deleterious mutations, and indicates that the individual's lack of interest in social or sexual matters is not simply part of having a damaged brain, but a matter of having developmentally a differently-and-inner-orientated focus.
The idea is that the Endogenous personality evolved indirectly to benefit the reproductive success of a group - so the Endogenous personality type should not be regarded as a pathology or a defect state, but as being evolutionarily optimized for creative innovation and problem-solving; therefore he would be expected to have the necessary enhanced abilities for this purpose.
So, the Endogenous personality may be recognized not just by their relative autonomy - that is, their lack of need for social validation and consequent uninterest in social and sexual matters - but also by their high intelligence and positive motivation to do (or to find) ... whatever it is that they are equipped by their nature to do.
In sum, the Endogenous personality is (at minimum) a triad of autonomous self-sufficiency, inner-motivation and intelligence.