In the last half a century or so, neuroscience, psychiatry and psychology have concluded that a great deal of the variation in the minds of individuals, call it neurodiversity (as the link indicates, the ideas in this essay are mostly not original), is hereditary or otherwise largely immutable, particularly by the time that people reach adulthood, and that these variations have a biological basis.
A reasonably systematic effort has been made to categorize the most extreme variations, to determine their causes within the brain, and to determine their prevalence and incidence. A considerable but less focused effort has also tried to assess what kinds of neurodiversity exists within people who are reasonably typical.
Many important variations in brain function manifest themselves as difference in the degree to which someone has a particular trait like intelligence or spatial visualization ability or tonal memory or neuroticism. While in time cases like intelligence, one extreme or another may seem to be clearly favored, in the case of many of these traits, there are pros and cons associated with each extreme of a trait. There are multiple traits that seem to vary more or less independently of each other, so one can speak of variation in brain function as being multi-dimensional.
Call the entire range of possible variation in people's minds "neurospace."
Neuroscientists, psychiatrists and psychologists, while no where near completing it, are already well along their way on the grand project of mapping neurospace, which is to say determing how many dimensions make up neurospace, where they extend, how heavily populated each region in neurospace is, the biological basis of these dimensions and which points in neurospace that might seem theoretically possible are ruled out by the underlying biological mechanisms that produce the traits in question.
These investigators have barely begun, however, the project that logically follows once one has a map of neurospace. How are different locations in neurospace relate to each other?
The emerging view is that there are meaningful and persistent relationship between different locations in neurospace. Neurospace as a whole, which is to say, the human race, can be viewed as a single organism whose survival is made possible by its neurodiversity. Within neurospace, some kinds of minds have ecological relationships with other kinds of minds. Some of those ecological relationships are mutual -- minds with characteristically male features and minds with characteristically female features mutually benefit each other; people with traits useful in selling things and people with traits useful in making things often find common cause; people who see things that aren't there can nurture and be nurtured by people hardwired to believe that a spiritual world exists. Some of those ecological relationships can be predatory -- psychopaths prey on people of conscience subject only to the risk of making the population too jaded to be vulnerable or exciting retribution from the collective action of their prey; the population genetics of rape are likewise apparent. The strong comorbidity of most mental illnesses suggest that they either have common causes or that there is so reason that flows from the ecology of neurospace that makes neurologically atypical people favor each other are partners in reproduction.
We are nowhere close to mapping out this ecology in any meaningful way. While we know that psychopathy and schizophrenia are relatively rare, while clinical depression and childhood ADD are relatively common, these are simply empirical facts whose causes we cannot predict or explain beyond the crudest population genetics based heuristic just so stories. We have no theory to explain why a particular percentage of people are extroverts while the rest are introverts.
In the absence of a meaningful ecology of neurospace, society is likely to dramatically depopulate, through selective reproduction, genetic engineering and increasingly effective psychiatric drugs and surgeries, much of neurospace on the grounds that neurologically atypical people suffer from disabilities that don't positively contribute to the human race and should be cured. The new eugenics will be kinder and gentler, but it seems nearly certain to emerge. The evidence on the degree to which the controversial practice of sex selection is employed in certain countries like China today strongly suggests that humanity will not resist the temptation to tinker with its own genetic makeup given the means to do so.
Sometimes those engaged in this new eugenics venture may be right. No one mourns the disappearance of dietary deficiency caused cretinism (lack of iodine is the culprit), and no one complains about the Flynn Effect (the secular rise in IQ scores from observed from one generation to the next which is believed to be mostly a result of fewer people having low IQ scores) whose causes may be related. Sometimes an apparent mental flaw is just that, a flaw.
But there are strong suggestions that many forms of neurologically atypical minds, which is to say, many places on the fringes of neurospace, may have value to the species in small amounts. We may need a sprinkling of psychopaths, bipolar individuals, novelty seekers, ADD adults and functional autistics to enhance the ability of the human race and communities within it to survive circumstances that appear infrequently but regularly in the long expanse of human history. Or, traits which are individually beneficial and need to remain in the genome for the human race to survive may be necessarily biologically independent and may as a result, inevitably come together in toxic combinations from time to time in a way that is impossible to change with simple minded eugenics.
While this is unlikely to be a matter of life and death to individuals, from a population genetics perspective it is the moral equivalent of such a struggle. Thus, it is likely that a group of highly motivated neurologically atypical investigators will emerge to better establish the ecology of neurospace, and that those investigators will be predisposed to find an ecological purpose for locations on the fringes of neurospace which is likely to exist precisely because these locations in neurospace still exist after thousands of years of homo sapien sapien evolution and millions of years of hominid evolution.
These studies of human evolution are also likely to discern what territory in neurospace in ancient, and what territory is seeing dramatic growth or is withering, and to determine why this is happening. Some of this change may be adaptive -- for example, traits strongly associated with reckless or drunken driving, an important cause of pre-reproduction death, are surely being relentlessly culled from the human race in favor of other more adaptive traits. Some of this change may be a result of maladaptive changes in modern life like exposures to toxins and reproduction by parents of advance age which our bodies are ill equipped to carry out. The evidence distinguishing these two possibilities from each other, and from the third possibility that apparent change is in fact simply a product of improved identification and diagnosis of particular clusters of traits, will often be muddy.
If these investigators fail at their task, we as a species may bumble into an ecological catastrophe within neurospace that puts our continued survival at risk. What if, for example, in an effort to stamp out or suppress psychopathy, which approximates the folk definition of inborn evil, we also deplete the human race's supply of ruthless leaders so deeply that we are unable to take the collective steps necessary to thwart the next devastating disease outbreak or a global warming driven climate collapse?
An improved ecology of neurospace is also probably necessary to better understand one of the great population genetics mysteries of our age: Why have the reproduction rates of economically comfortable and powerful people have fallen so dramatically relative to the poor and the powerless? Why do unemployed felons frequently have many more descendants than Presidents and corporate CEOs? Why has this phenomena emerged now when for millenia until just the last century or two, the reverse was clearly true? Why does declining fertility almost universally accompany economic development in a matter of just a generation or two?
The temptation to tinker with the makeup of the human race is insatiable. Indeed, every time men and women at a nightclub size each other up as they try to determine who is most desirable, we are tinking with this very dynamite. But if we gain an increased ability to do so in an organized and precise manner, we could end up with the same monoculture risks that are currently putting the most commercially exploited version of the bannana at risk of extinction, despite its numerous qualities which humans find desirable in them.