If not, what are some presumed causes for differences between individuals?
Upbringing, presumably?
Most behavioral traits are inheritable to some degree yet environment also has an impact. That is the crux of the nature/nature debate. In the old days (the 1960’s and before), many psychologists believed that environment was far more powerful than biology but we know that really isn’t true now.
For questions of this type, the gold standard for research in humans is with identical twins raised apart. I am not sure why anyone does that but there are many worldwide and they tend to show that most behavioral traits are remarkably consistent regardless of the environment. One criticism of these studies is that many of them are done with Scandinavian twins that are simply raised in different towns or cities with roughly the same culture but the psychological similarities are usually striking.
Google ‘identical twin separated at birth studies’ if you want to know more about this. Your overall question is still a bit of a mystery though because psychology and neuroscience is still debating many parts of it.
I’d have to see a cite that “most” behavioral traits or consistent in twins in these studies.
We could get into semantic squabbles here, trying to define where “emotionality” ends and “mental disorder” begins. Take chronic depression in particular. This very definitely seems to run in families – even extended families, including multiple generations and cousins, second cousins, etc.
Okay, that still leaves some wiggle room to argue it could be upbringing – Grandma is depressed, kids learn to be depressed by their “nurture”. Then the kids’ kids get it likewise. Then their kids (the cousins) get it likewise. But something in the DNA seems the more likely culprit, when so many in the extended family are like that, and when it becomes apparent in many of them at a young age.
This still also leaves room to debate where “emotionality” ends and “mental disorder” begins, thought.
It would help to pin it down with maybe why do you ask?
What? I don’t understand.
Let’s try this. Is there an example or a person you are thinking of? It’s a very big and at this time generic topic.
But the short answer if that is what you are looking for is YES.
I would love to but like the OP, this is a very large field and still a developing one. There isn’t a single cite for it. There are academically oriented books that survey the research and provide the current state of knowledge. I can give you some good examples of those if you wish but the interaction between biology/genes/environment is one of the most complex topics that exists.
Here is one pop news story that is nevertheless backed up by real science:
Amongst non-human primates, there is both variance within the the population and between populations. So individuals surrounded by gregarious individuals are more likely to be gregarious themselves. Individuals born of a gregarious mother (easier to track than fathers) are more likely to be gregarious as well. However, like with humans, personality can vary and change depending on circumstances. I’ve seen a monkey go from a sweet, kind individual to a total bitch upon taking the ‘alpha’ role.
A study of alcoholism in rhesus macaques found that individuals born of an alcoholic mother were more likely to become alcoholic themselves, unless they were given to a mother with a better temperament, who didn’t suffer from alcoholism herself.
Genetics and the environment are important; both influence the other.
I still don’t quite understand. How would studying one person tell us whether the trait is inheritable across a population?
I wasn’t thinking of anyone in particular, no, just people in general. Although of course I hope the results can be extrapolated to our daily lives in understanding ourselves and each other.
I don’t know about emotionally, but there are a lot of traits that run through my family from my grand parents through their great grandchildren. There are 5 children, 10 grandchildren, and 10 great grandchildren. Out of those I think most of them twirl their hair, and have since they were babies. We also all bite our fingernails quite a bit.
I would say at least half of us have both of these traits, and almost all of us have at least one of them. It’s quite funny to sit around at a family gathering and watch half of us twirl our hair. As babies, under a year, a few of us would rip our hair out of our heads, there’s no way that’s learned since none of the adults do it.
I know that’s not emotionality, but it wouldn’t surprise me if it was more DNA then learned.
I imagine things like bad temper, depression, etc. are inherited to some extent. Of course, early training is a powerful changer of behaviour, even if it only changes the surface veneer and the underlying emotion is still there.
Two examples come to mind - wife-beating and hockey fights.
Until about 20 years ago, domestic violence was something that rarely go addressed by society. Some guys would lose their temper and beat their wife, even over the most trivial things. I twas my observation that the second most prominent, most frustrating person in most people’s life is their boss; yet almost nobody punches out their boss, and if they do, they only do it once. (Unless they snap and bring a gun to work and solve the problem for 20 t life) Social conditioning trumps basic nature - no matter what the instinctual urges, people can control themselves when they know they must.
Hockey players are the same - every other sport, you fight or even throw a punch, you’re out of the game with big fines, even a rough contact game like football. As a result, very rarely are there fights. Yet hockey is somehow magically different and fighting is necessary to release steamor whatever. However…! The group probably as frustrating and difficult on-ice as the opposing team are the officials. (Just ask the hockey moms). NOBODY EVER takes a swing at the officials. The extremely rare occasion they do, they are OUT. Again, people do what they can get away with, and restrain themselves when they know they must.
The best example that fits the OP’s question - I worked for a while, way back when, with a fellow who grew up on a farm before the age of political correctness. He said there was a lot to be learned by observing animal behaviour. He mentioned that personality seemed to be established pretty much at birth; you could a group of puppies, all from the same litter, same parents. Even at birth, some were nasty and would try to attack you if you handled them, and others would be friendly no matter how you treated them. His theory is that some temperment is inherited, some is accidental development. (He also mentioned it was not unusual to see male animals humping males, but that is a different debate).
I suspect there are a number of factors that determine personality, some dominant, some not; so just like we “look like” our parents to a variable degree, we inherit some of their personality traits. Unlike the pop psychology of the mid-1900’s, I doubt much of the behavioural traits are “learned” or imprinted by early childhood trauma.
Hormones affect emotions and mood in adults. Prenatal exposure to hormones and hormone-like substances might have something to do with emotionality. Other things like digit ratio (the ratio of the length of your index finger to the length of your ring finger) are influenced by prenatal hormone exposure.
A clear definition of “emotionality” would be helpful, here.
I think the problem is the word ‘most’. There’s plenty of evidence that twins raised apart show ‘some’ common characteristics.