I think researchers have a clear distinction that populations are an altogether different phenomena than individuals. This is something that the public often confuses, as demonstrated when somebody rebuts a statement about population attributes with a personal refutation. This is a failure to argue on the same phenomena.

Researchers are also aware that personality changes population-wise with age, and also that individuals also experience personality changes -- but generally not in a medically interesting way in the sense of a reliable and precise intervention to effect positive changes.

I'm also reminded of studies on the transferability of personality traits with adopted children (no significant correlation! amazing! same correlation with biological parents compared to those children raised by their biological parents), or reared-apart monozygotic twin studies, or reared-apart dizygotic twin studies, and so on. The collective portrait of many data points suggests a set of stable biological factors to personality, as opposed to personal experience.

Think of your personality a barren landscape, which starts out with very, very minor depressions and irregularities. These depressions and irregularities might so so small they're not even be perceptible to the average person walking across it. Over many years, rain will erode these minor features into gullies, and if conditions are right, you can even end up with canyons. The course of a mighty river can be entirely determined by minor irregularities in the starting landscape.

Of course, if you took a decent sized plow and cut a channel through the landscape early enough, you could direct the development of the river to exactly where you wanted it. If you wait too long, redirecting the river becomes a major engineering task; involved, but still entirely doable.

I mentioned a few studies, but worded them poorly, but I wonder what you think about the fact that there's no significant correlation in personality traits between foster parents and their adopted children (fascinating, no?), and that these children have the same correlation with their biological parents regardless if they are raised in the same household or with foster parents.

Shouldn't the unique experience of an entirely different household have some effect on personality?

Our genes do influence the development of brain structures that strongly influence general happiness level, sociability, and a variety of other traits. Under normal circumstances, the wiring of those neural structures tends to be reinforced. For example, friends and family members might observe a loved one who is not by nature sociable and say "you are an introvert" or "you are shy" which is a reinforcing stimuli. When that person has heard this enough times, whenever they behave in an unsocial manner, they will tend to explain it by thinking "I'm shy/an introvert" thus perpetuating the neural structure. If instead, sociability is treated as a skill, and correct behavior is reinforced while incorrect behavior is punished, over time those neural structures will be re-wired.

This pattern is observed all the time for tastes. We have genetically predetermined preferences, but overwhelmingly what we end up liking is the result of social conditioning.

That doesn't really seem to address the issue of adopted children though. If I understand you correctly, the social environment (and conditioning) of the children should override the biological aspects of their personality. Or at the very least it should have a very significant effect.

It seems to me that certain aspects of a person are very malleable, taste being one of them. But many other things apparently are not (IQ, or various other measures of 'intelligence', if I recall correctly).

From my experience in the social sciences, we tend to underestimate the role of genetics more often than not.

It does address the issue of adopted children - we as a culture have a fixed mindset for things like introversion and intelligence, and genetics do strongly influence our default level of both of those. Thus, adoptive parents observe the child and say "you're an introvert" or "you're not clever" and the default pattern is reinforced.

On the other hand, when a child displays an initial dislike for like Taylor Swift, her friends might say "you're crazy, Taylor Swift is awesome."

It's all just neural networks being reinforced or inhibited, the primary contribution of genetics is the default state of the network. In the case "fixed" personality characteristics, our culture is to reinforce the default networks, while for things we view as mutable, we have no qualms about training away default behavior.

Why should "introversion" be changed or punished, necessarily? Developing intellect is something to be encouraged, but I don't understand the anti-introversion bias in your post.

And I suspect that the genetics does also set a limit as to how far one can bend, too. This too, will vary between persons.

Seriously.

"Entrepreneurship doesn't happen. The data are very clear on this. Most people who start businesses fail."