Ideas about human improvement include higher intelligence, stronger special talents, even questionables like telepathy. Another might be the ability to intentionally change the personality by mental action.
Created personalities, unlike multiples, would be neither involuntary nor pathological. They would be distinct persons, based in the same memories and abilities, although they might not be as noticeable as it seems.
In fiction Stevenson’s 1886 classic The Strange Case of Dr. Jekyll and Mr. Hyde features a potion that divides personalities into opposites. Like case studies recent treatments usually attribute multiple personalities to sexual trauma.
A Twilight Zone episode that aired in January 1960, “The Four of Us Are Dying”, is a better metaphor based on physical change. A man can completely alter his features, taking on the face of anyone he sees. Nobody can tell he isn’t the person copied so he uses his talent to get out of trouble. (In Rod Serling’s implacable morality he unwittingly copies the face of an intended murder victim while doing so.)
Therapy obsessed Western societies haven’t come up with or at least kept the idea as a positive goal though the seed is there. Christianity always held the promise of spiritual renewal and ultimate perfection, possibly one reason the Left attacks it. Psychoanalysis and its spawn held out a materialistic version at the expense of creativity and confidence. Psychedelics did the same. Authorities want competent workers and try to stifle or control whatever might produce wholly functioning persons.
Cases show that some capacity for multiple personalities exists though the line between unconscious responses and deliberate lies is murky. Supposedly the pathological results of emotional trauma, multiples seem an updated version of what used to be called hysteria and conversion reactions.
People have some ways to deliberately change. A few, learning skills or acquiring and dropping habits, sometimes imitating others, are internally controlled. Usually they require going outside oneself: changing environments, joining religions, entering therapy.
Especially if they lack ethical convictions people need an external lever on themselves. A stronger consciousness of one’s own conflicts and of what in others’ behavior are responses to one’s actions would help internalize the process.
Developing and switching separate personalities would require the ability to intentionally reorient emotions and behavior patterns. Personality factors would have to be deactivated without repressing or deleting them so they could be reused. To do all that demands a stronger, more comprehensive ego in the psychoanalytic meaning of reality orientation.
Since they wouldn’t be pathological dissociations the personalities would have the same memories but with different meanings. Their emotional structures and characteristic behaviors would differ as much as those of separate individuals. THey might occupy part or all of ons cell network with synapses activated and inhibited in different patterns.
While the personalities would be recognizably distinct it’s unclear how deep their differences might go. Some elements like the extraversion and introversion dimension might be determined by inflexible structures. So might others such as vulnerability to phobias and addictions. Obsessive-compulsive behaviors may be centered in old brain modules outside the personality.
After a change individuals might become slightly difficult to recognize because of different habits, interests, and to an extent different vocal and kinetic styles. The current personality could truthfully deny having done what another did.
Skeletal and muscular systems limit changes in movement and speech. If the body is color blind, deaf, diabetic, or has other conditions so will the personalities. Hair and skin tones, age, scars, teeth, and such will be constant and so, of course, will fingerprints and DNA.
A stronger, overall identity, separate and likely not apparent to other people would have to control the personalities. This ego would from an early age need more self-awareness and insight into how others respond than now common. Others would deal with it through its and their own personalities.
It would be more rational than the personalities and more so than most people today, more capable of keeping to an ethical code, less given to defensiveness and rationalization, and not as influenced by emotion.
Such persons would be more empathetic than is normal today and recover more quickly from difficulties. They would certainly be more adaptable. They could detect and eliminate negative behavior in themselves rather than maintain them because the ego would be above the identities.
Relationships, even marriage, might be more satisfactory. People could work more effectively together without that effort permanently changing them; employers might specify the personal styles they need in employees.
As children these persons would move quickly from trying out behaviors to experimenting with personalities. Able to distinguish voluntary actions from identity, they could learn early how others not only feel but what they likely know and intend. They may develop personalities that don’t now exist, while some now common behaviors might vanish; of what use would hero worship be, for example, when one could become the hero by mental effort?
Role playing would alter and people might invent personality games that can’t now exist. People might change in group patterns or agree to take on certain traits for certain occasions. Drama and fiction would change. Individuals would likely have extensive wardrobes for their several personalities….speculation is difficult.
A more complex brain than now common would be required. Early developing objectivity about oneself and a totally dominant ego would probably be more demanding than several personalities, which seemingly can exist today. There will be more neurons but especially many more connections.
The necessary mutations might arise by chance and combine only gradually except in small populations. Except for self-control and intelligence they might not necessarily have immediate survival value.
Smart disciplined persons would become prosperous and powerful in organized tribes. Multiple personalities seen in children might make the latter seem dangerously unreliable. Some might become shamans and culture bearers of various types or be capable of swift adaptation to other tribes. Overall distrust would probably work against developing multiples.
In civilized states with populations too large for everyone to know everyone else bringing various social roles and conflicts they would get less notice and be more adaptable. Empires with extensive bureaucracies, many occupations, religions and cults, and subcultures would enable them to flourish. Setbacks as in the Dark Ages and widespread plagues might limit them but they would have developed ways of being safe and useful. Only recent bioscience techniques could by then detect them.
If genetic engineering can develop such persons they might be seen as having desirable traits. In that case the mutations would spread more rapidly, by both artificial and natural means, though government will try to limit such smart and versatile persons to its own uses.