A newly published study in Behavior Genetics describes the genetic heritability of a vast number of traits based on measurements of 772 pairs of twins (half identical, half not). The basic concept here is that if a trait is largely genetic, it will be more closely shared by twins who have identical physical and cognitive characteristics. Conversely, non-identical twins will inherit only smallish and random bits of each trait.
The study incorporates thousands of traits, most of them related to brain volume and structure based on imaging studies. However, it also includes quite a few of more general interest. Here's a selection:
Overall cognition, which is basically intelligence, is about 70% inherited. The other 30% is influenced by shared and non-shared environment. The same is true for oral reading. The subcomponents of intelligence, fluid and crystallized cognition, are a bit less inheritable.
Hyperactivity is almost entirely inherited. Anxiety, by contrast, is only weakly inherited. It's apparently caused mostly by environmental factors.
Reading for pleasure is almost entirely influenced by genes. Oddly, though, listening to music isn't.
Thanks to the size and breadth of this study, it's basically state-of-the-art among classical twin studies. More modern GWAS studies will likely supplant it in years to come, but so far they've surveyed only 15-20% of the human genome. For now, this is about as good as it gets.
gotta say the reading for pleasure number is suprising to me. i would have guessed my own reading for pleasure was highly environmentally driven.
Yeah, same, that one's fascinating.
Not liking to read was treated as something close to a moral failing in my family. Despite loving reading, once I was old enough to have some context, I thought that was pretty oddly judgmental. Now I find it is flat out wrong and "readist".
Reading for pleasure is something that can only have come about after something you could read for pleasure was created, so it's evolution by recorded history.
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A fascinating study. It will be interesting to follow these studies as they add more characteristics to them.
Both of my parents were hard-core conservatives, and I'm about as liberal as it gets. At this point in my life, I believe that political orientation is largely inherited, but authoritarians can be changed to liberals with enough education and intention.
My father used to tell me, "We never should have sent you to that liberal college."
Lol. Going to that liberal college made me what I am today, thank god and, unintentionally, my father.
At birth, it's probably safe to say 100% of you is your genes. I think the more interesting observation is how much of you is your genes at age 90.
According to nih.gov, roughly 999 base pairs out of every 1,000 are identical in every human being. That means that the hardwiring in our brains is, to a large extent, identical. I'm referring to the read-only, as opposed to read-write wiring.
"Overall cognition, which is basically intelligence ... "
Is that true? Are you sure? If that's true, explain Elon Musk, Ron DeSantis, Ted Cruz, Vladimir Putin, and etcetera. These are all, in my estimation, intelligent people. How does someone that is not intelligent get into Harvard, let alone pass the bar with a Harvard law degree?
Is it plausible to assume that "overall cognition" is a combination of wisdom and intelligence, and that the two are separate functions that are supposed to be working together, and not at cross purposes? If that is true, then a person can be highly intelligent and incredibly unwise. That's how I explain the above-referenced characters.
As for Donald, I'll accept Mary Trump's assessment that he's not all that intelligent. But he's smart enough to take advantage of the fact that most people studiously ignore what is self-evident to me, which is that wisdom is not intelligence. You don't have to be all that smart to use that knowledge as leverage. All you need is someone evil, like a Roy Cohen, to point the way.
If I'm right, then God save us if an intelligent POTUS decides to follow Donald's lead.
So, although I don't dispute the idea that the survey contains new and useful information, you can count me as one person that does not think that it is as good as it gets.
"That means that the hardwiring in our brains is, to a large extent, identical."
That is just wrong.
At the level of neurons, you cannot match between individuals inside the cerebral cortext. It is completely different across individuslas.
The similarities are features of few millimeters magnitude, but that doesn't determine the actual information procesing. The information processing is determined by the patterns of connectivity between neurons, and this is unique to every individual.
I can't say for sure that it's impossible to match between individuals inside the cerebral cortex, but I think it's safe to assume it is.
I agree that cognition is determined by patterns of connectivity between neurons, but how do you know that the patterns are unique to every individual? To prove that, you'd have to do what you've said is impossible. Also, your statement sounds a lot like the blank slate theory.
Suggestion: Read Steven Pinker's The Blank Slate: The Modern Denial of Human Nature (2002).
We have tons and tons of data both from mice and humans to show clearly that you cannor match neural connectivity across individuals below millimeter level.
It is not actually possible to prove such negative assertion from one experiment, but bassically all experiments that could have found mathcing connectivity haven't actually found, and there are enoough of these to make matching connectivity impossible.
The blak slate theory states that all humans start the same (as a blank slate). What I am saying that they are all different, so it is not the same.
Pinker doesn't understand neuroscience.
I'm not the biggest Steven Pinker fan, but am I supposed to just accept your opinion that you understand neuroscience and he doesn't? I'm still thinking you're a blank slate advocate and you don't understand Pinker's position or what the term 'blank slate' means.
You say that there's no commonality in neuronal connections between individuals. Doesn't that mean that our behavior is an expression of neuronal connections that are formed entirely via nurture and not via inherited nature? That is the blank slate theory. Pinker's book is about the evidence that there is a nature component. His book convinced me, but the evidence in what I see with my own eyes is overwhelming.
" but am I supposed to just accept your opinion that you understand neuroscience and he doesn't?"
No. You are supposed to go and read some textbooks of neuroscience so you understand the subject better, and then yo can (easily) see it yourself.
If you think that is too much effort, then there is no way I can convince you. There is no argument that can overcome lack of knowledge of the actual facts.
These comparisons are based on certain limited tests, which are assumed to be influenced in some way by the stated characteristic. "Cognition" for example means scores on a certain test or tests. You have to read carefully about the tests to see what the category means. In some cases test results are correlated with specific achievements by test takers, but in many cases they are not. Some things like height are very straightforward, but what is "crystallized cognition" and how is it accurately measured? Don't make too much of all the specific categories.
Whereas fluid cognition reflects the capacity to solve novel problems, and process and integrate information, crystallized cognition reflects the knowledge and skills acquired through education and cultural experiences (Baltes et al., 1999; Horn & Cattell, 1967; Horn & Hofer 1992)
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I find the idea that anyone can measure anything called "overall cognition" fairly dubious. And then putting heritability percentages on such a poorly-conceived concept really takes you to the land of the ridiculous.
And the heritability of "reading for pleasure" tells you a lot about how seriously to take this. I wonder which of my caveman ancestors were big pleasure readers.
772 pairs of twins (only half of them identical!) for thousands of traits. This is a massive statistical nightmare.
It means that many of the individual-trait results are incorrect by sheer statistics. It could explain the reading for pleasure vs. listening music conundrum. Or that "components of intelligence" seem less inheritable than "intelligence".
The fact that there are no confidence intervals in the graph only enforces my skepsis.
This is the type of thing that easily leads to everyone going bananas, for obvious reasons.
Before that hits, my point would be that even if "cognition" is 70% inherited, it does not follow that (1) for the 30% who do not inherit whatever genetic cognition one or both parents have, what they do inherit? - is it less cognition or more cognition?, and (2) everybody cannot be, and does not have to be, a college statistics professor.
Whether we ought to worry about a a population where 70% of someone's cognition is inherited, and the population wide results of high-cognition v. low cognition is so rarely discussed.
As a parent of a special needs kid, who would have simply been labeled dumb a generation or two ago, I think about this alot.
The idea is not that 70% inherit their parents' cognition and 30% do not.
It is that 70% of the population variance is due to inheritance and 30% is due to environment.
This says nothing about any individual. You may test higher or lower in cognition than they do and it may be due to genetic luck (you got the best / worst chromosomes from each of them) or due to environment (you had a good stimulative environment while they were raised by madmen who kept them locked in a box for most of their childhood or the reverse).
I'll go out on a limb and predict this study will not settle the longstanding nature-vs.-nurture debate. But it does get you thinking.
Where the study says height is 95% determined by genes, that sounds about right. But I'm not sure what to make of the "reading for pleasure" and "music listening" numbers. What do those behaviors even mean?
Does reading cover all reading outside of school or work? Books (fiction? nonfiction?), newspapers & magazines, the internet? Can we agree that Twitter & FB don't count? Likewise, with music. Music seems ubiquitous to me. Is there anyone who doesn't listen to music? Or are we just talking about people who take time and effort to feed their particular musical tastes?
About 4 of 5 people around the world were illiterate until 1900, roughly, and through 99% of human history no one read. So reading as a behavior seems highly environmentally based to me. It is culture-driven more than genetic, right? I don't understand where the study is drawing a line.
I would guess the ability to hit a 100-mph fastball 400 feet over a wall is a skill (behavior?) that is almost entirely genetically based. Except for a very select group, no amount of time in the batting cage will make a difference. But having the right genetics isn't enough either. It still takes umpteen hours in the cage, top-rate coaching, and a culture that values that particular skill. Which excludes most people in the world today, and almost everyone through human history.
It's easy to show where genetics is a critical and predominant factor. But my guess is that's true really for a few traits at most. I wouldn't say we're mostly blank slates. But we're creatures of culture far more that we suspect. (Especially in the US, where the culture tends to mythologize the rugged individualist ideal.)
Btw, there was a good documentary a few years ago that's worth a look for some insights into nature vs. nurture. Three Identical Strangers. Fascinating and heartbreaking.
It's a good study, but twins, identical or fraternal, tend to inherit the same parents and get raised by them in the same household. The folks doing the study make the most of what they've got which is nice. The results look reasonable, but I have to take them with a grain of salt. If we didn't know better, we could prove that the ability to speak English or Chinese is highly heritable as opposed to a matter of what language the child's caretakers use.
I think studies like this are very interesting, but I always worry about the ways we've seen people make use of them. Relying on genetic analysis can be like assessing a car based on its engineering drawings as opposed to driving it around a bit. India took this to an extreme with its genetic caste system which just happens to work to the benefit of a certain group of castes. There are lots of people ready to jump on any scientific results as an excuse to impose their own similar system.
I think a twin study would actually prove that ability to speak English or Chinese is highly dependent on environment.
Fraternal and identical twins will differ very little in how likely one twin is to speak English / Chinese compared to the other - if one speaks English, the other will almost always do so whether fraternal or identical. The same for Chinese.