Maggie's Farm

And a response in the same publication, There Is No Nature Nurture War:

https://blogs.scientificamerican.com/beautiful-minds/there-is-no-nature-nurture-war/

The author addresses 12 statements Plomin has made, including several in the article posted here. Here is one example - everything below is quoted from the article:

2. "For most of the 20th century, environmental factors were called nurture because the family was thought to be crucial in determining environmentally who we become. Genetic research has shown that this is not the case." (From In the Nature-Nurture War, Nature Wins)

How could Robert Plomin of all people say such a thing? This is not what the shared environmental findings suggest, and most psychology professors go through great pains to emphasize this to their students in Psychology 101! What the evidence actually suggests is that families don't generally make siblings more similar to each other, or they only do to a small degree and only for specific traits. And to the degree that they do, those traits tend to diverge when children leave the home. Judith Rich Harris famously reviewed that evidence in her bestseller, The Nurture Assumption.

But that's absolutely not the same as showing that family does not matter in terms of who we become. That conclusion simply does not follow logically from the scientific research. As the developmental geneticist David Moore and I put it in our 2008 article, What Makes Us Who We Are?:

"Take the most essential element: a child needs to be raised in a family, almost any kind of family, to develop the ability to speak a language. Since every single person in twin studies checks that box (i.e., is raised in a family of some sort), this factor never varies and thus does not predict differences in ability to speak a language. But does this mean that the variable "has a family" doesn't matter in determining whether or not a person develops the ability to speak a language? Of course not! That's like saying that water has no influence on a fish's development because all fish live in water. Just because a variable doesn't vary doesn't mean it has no causal impact on a particular outcome. The parenting factors that are statistically associated with differences between individuals should never be confused with the parenting factors that cause the development of a trait within an individual. Genes could "account for" 100% of the variability in a trait in a particular twin study, but this does not mean that environmental factors are therefore unimportant in the development of the trait; parents still matter and will always matter. It turns out that parenting matters, just in a way different than originally assumed. Genes matter to the extent that they support parenting because like any other behavior, parenting behaviors are influenced by the genes ”and parents matter to the extent that they support the expression of genes."

Furthermore, for traits like IQ that are only about 50% heritable, even if there are no effects of the so-called "shared environment," parents may nonetheless be an important part of the so-called "non-shared environment," as long as the effects they have on their children tend to make them different from each other. This may seem counter-intuitive-- surely given that children in the same family have the same parents, then parents must be part of the shared environment-- but that is not true because of the technical meaning of "shared environment" in the models used to estimate heritability. Again, only forces that make children in the same family more similar to each other count as "shared environment," so the present state of scientific knowledge means that parents may be important in influencing their children to become more unique.

Hey, AVI!

There were 12 good points in the article I linked pointing out limitations and contradictions in Plomin's claims. What's taught in Psych 101 wasn't actually used as evidence but rather to emphasize the author's surprise, I thought.

Anyway, I think the criticisms of Plomin are valid. In the point above, DNA only gives us the ability to learn a language, growing up in an environment that teaches us a language is essential. What are the differences in the lives of a person with fluency in a language vs. a person with no fluency in any language?

Sure, any family will teach the children a language, so that is discounted as 'nurture' because it doesn't differentiate. I.e., it is only true because it is defined as true. Tautologies aren't that meaningful as evidence, though.

Let's take another example (again, everything that follows is quoted):

3. "We would essentially be the same person if we had been adopted at birth and raised in a different family. Environmental influences are important, accounting for about half of the differences between us, but they are largely unsystematic, unstable and idiosyncratic”-- in a word, random." (From In the Nature-Nurture War, Nature Wins)

Again, it's impossible to make this claim based on what we currently know about genetics. Not only that, but these two sentences contradict themselves. First he says we would be the same, but then in the very next sentence he says of course we wouldn't be the same. What he is basically saying in these two sentences is the following: "You would be the same person if you had been adopted at birth and raised in a different family if that family somehow was in exactly the same situation and experienced exactly the same environmental forces your entire life as the family you were adopted from." This seems pretty unlikely based on how the world works, and seems like a pointless comparison anyway.

Plomin seems to think that because environmental influences are "largely unsystematic, unstable and idiosyncratic", that somehow they just don't happen. Or that they would happen in exactly the same way no matter where you lived. That is an inherently contradictory perspective. You couldn't possibly be the same person if you had been adopted at birth and raised in a different family even if the family itself had no influence (which is a false claim, anyway), precisely because of the real existence of all of these unsystematic effects! In other words, it's the existence of the very environmental effects that he acknowledges that invalidates his own claim.

Additionally, it is simply not true that all influences of the environment are "unsystematic, unstable, and idiosyncratic," even if many of them are. As we'll return to below, research using natural experiments has shown that every year of education causes an increase of approximately 1 to 5 IQ points. And research on personality provides evidence that a number of life experiences-- including beginning one's first romantic relationship or starting one's first job-- have a systematic and lasting effect on personality traits.

Well, I haven't read Plomin before his article was posted here, so I think it's a good bet I don't understand him. But, I like talking about his article and I'm willing to learn and adapt my ideas.

Actually, I think the language point is a good one; just because we can take something like language learning for granted doesn't mean it's not important. It's kind of circular to suggest that nothing that we can take for granted in nurture is important, but genetics (which we can entirely take for granted) is important, isn't it?

The point about twins is interesting; the critic's last point was that the family may be important because it increases differences, and that's what twin studies seem show. When identical twins are raised together, they show more differences in personality than twins who are raised separately. So it may be that we are looking for the wrong thing in the environment side of things.

I think one problem is we're seeing here is the idea that the only things that are important are the ones we can quantify. If they can't figure out a database category for it, they don't want to think it's important. But life is messy, and I think that attitude is a form of intellectual blindness. This is similar to the opposite problem you bring up with psychology research not wanting to consider genetics. That goes both ways.

Actually, I think that we do know that some environmental factors do influence gene expression. I posted on that at Grim's some time back. I'll try to find it.

Sorry, I was thinking about circularity and got that stuck in my head. I meant contradictory.

So, the second sentence of the second paragraph should read:

"It's kind of contradictory to suggest that nothing that we can take for granted in nurture is important, but genetics (which we can entirely take for granted) is important, isn't it?"

Hi, Stargazer,

Thanks for the recommendation. I've added it to my Amazon wishlist and I hope to read it over the summer sometime. I have a list of books to get through first, though.

If you have 20 minutes, check out at least the first video in the post I linked in comment #10. There are 3 videos, so that's an hour of your time, and I'm impatient these days; let me read it and it's so much faster.

But, the key point is, our environment affects our genes, too. Watch at least the first one and you'll see more of where I'm coming from on this.

Here it is. I'm afraid the information is in a series of TED talks, so it takes time to get through. The talks are by a professor of human genetics, a neuroscientist, and an evolutionary biologist, and the point is that environment affects our genetics.

The Interdependence of Nature and Nurture

Thanks for pointing this distinction out. I'm reading up on epigenetics and will come back later in the day.

OK, I feel somewhat more informed, though I haven't had time to read in depth.

If by "nature wins" we mean the early Environmentalists lost, yeah, OK. They were wrong; genetics is far more important than they supposed. I guess that's why nature wins against nurture, specifically.

But I don't make the assumptions of those Environmentalists, and if we're talking about a broader conversation than that one, I think it's 50-50, and I don't assume that just because the environment side is unsystematic that it's unimportant.

However, I think from that position, I'm not sure how relevant Plomin's article is; maybe we need some younger scientists who are not caught up in early-mid 20th century arguments to update this discussion.

Or maybe I have no idea what I'm talking about. Clearly, I have a lot of reading to do to be well-informed on this debate.

And thank you. I appreciate a good conversation!