If you want to get strong, you exert your muscles in a way that you want them to develop. Want to be able to lift a lot? Lift heavy weights a few times. Want to be able to lift for a long amount of time? Lift lighter weights many times. While this seems almost overly simplistic, the underlying response of your body is incredibly impressive: your biology gradually shifts to account for the new demands that your activity places upon it. Breaking down muscle tissue frequently sends a message to your body to rebuild that muscle tissue, and more strongly.
If you want to become friendly, what should you do? Exert your friendliness muscles, so that your brain rebuilds itself more friendly-ly? Potentially. Currently, personality change theory posits that biological change is a main pathway towards personality change (Roberts & Jackson, 2008). The classic example of this comes from Phineas Gage, a miner who took a steel rod through the noggin’ and turned into a hostile, cold person. Presumably, this was because areas of his brain responsible for aggression inhibition were damaged. So one easy way to mess with personality is to lobotomize people. Unfortunately, that’s probably not going to improve the traits that are considered socially desirable, it’s going to make things worse.
By coincidence or not, a basic tenet of exercise (work what you want to become strong) also applies to neurobiology (the neurons that fire together wire together). So, potentially, repeated or intense activation of neural circuitry implicated in friendliness can make a person more friendly. That’s cool! Here’s where we can begin using what we know about exercise to extrapolate theory about personality change.
First is that exercise benefits are contingent on accruing a critical mass of exercise. Running a single mile one time will not make a person healthy, and neither will performing a single act of kindness make a person’s baseline friendliness increase.
Second is that there are different ways to work the same muscles. Specificity can vary. Curls, the bench press, and pull ups all work biceps. Presumably, repeated practice of any activity that targets friendliness can make a person more friendly. However, it may be that intensely specific exercises are not able to trickle-up and affect people at the trait level. If you practice keeping a calendar, you may not see effects at the level of your entire conscientiousness trait (especially if the questionnaire doesn’t include any questions assessing keeping track of dates, such that real change in your latent conscinetiousness may not be picked up on, but that’s a whole nother issue).
Third is that there may be trait “steroids.” What limits improvement in strength training? One factor is that the body rebuilds itself slightly stronger each time muscles are worked. It would be evolutionarily disadvantageous for a person to go from skinny to Ahnold in a single workout, because their body would OVERcalibrate to the environment and be similiarly maladapted. Similarly, it would be disadvantageous if a person practiced approach behavior (i.e. extraversion) a single time and then became the life of the party — they would be maladapted to approach situations. It is good that our biological systems limit the progress of change. However, steroids have been developed to increase the rate at which muscle is rebuilt and to increase the amount of muscle that is rebuilt after a workout. A person can drastically improve their fitness if they are willing to deal with the side-effects. Are there trait steroids? Hallucinogenic drugs may be steroids for the trait openness. One study found a HUGE effect size for increase in openness following psychedelic mushroom use (Mcsomething, blah blah). Another unpublished study found that marijuana use codeveloped with openness (Robins, personal communication). And associative networks, implicated in creativity, seemed to expand when people took LSD and named objects on a flash card. Just like steroids, though, there may be side-effects of boosting openness — apophenia, or false-pattern perception, increases as openness increases. That could be why people on hallucinogens see visual hallucinations, but too much false-pattern perception may be detrimental to everyday life (consider the everything-is-connected paranoia of schizophrenics (or your stoned friend in college)).
What is clear is that this is not a perfect metaphor — biological systems promoting neural connection are not the same as biological systems promoting muscle growth. But this exercise (pun intended) may stimulate further thought that can help us develop theories of trait change.