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Science: Nature vs. Nurture

Rob Stein
Washington Post Staff Writer
Monday, February 9, 2009 11:00 AM

Ever wonder what makes a bigger difference in a baby's life, nature or nurture? Post staff writer Rob Stein and Cardiff University researcher Frances Rice were online Monday, Feb. 9 at 11 a.m. ET to discuss a recently released Cardiff University research project that used "test tube" babies to try to answer the question many ask.

Read the story: In Vitro Fertilization Offers New Lab for Studies (Post, Feb. 9)

A transcript follows.

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Rob Stein: Hello everyone. Thanks for joining us today to discuss this fascinating new piece of research giving us new insights into that old question: Is it nature or nurture? Joining me today is Frances Rice, a lecturer in developmental psychology at University College London, who helped conduct the new study. Rice and her colleagues studied babies conceived through IVF to examine whether cigarette smoking by pregnant women increases the risk their babies will have behavioral problems. I see there are already questions waiting for us, so let's get going.

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Maryland.: Nice study design. Did the researchers offer any explanation for the elevated antisocial behavior in children of nonsmoking mothers who received donor eggs?

Rob Stein: Interesting question. One possible explanation might be that the donor eggs came from women with a genetic predisposition to antisocial behavior, so the resulting children were born with that tendency even though their birth mothers did not smoke or have that predisposition themselves. This would certainly be consistent with the idea that the antisocial behavior was the result of an inherited predisposition rather than having been born to a mother who smoked while she was pregnant.

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San Gabriel, Calif.: Does nature or nurture play a dominant role in explaining the 4 to 1 ratio of autism in male children vs. female children? In other words, what explains the occurrence of autism at a much higher incidence in male children than in female children? Anything to do with mothering patterns?

Frances Rice: This is an interesting question as you rightly say, boys are much more likely to be diagnosed with autism than girls. This increased prevalence in males is also true for other neurodevelopmental problems as well as for autism . It is difficult to say whether nature or nurture is more important. Clearly, inherited factors are important in autism - twin studies show that it is highly heritable but other factors contribute. Researchers in Cambridge, UK have a theory that the amount of testosterone that babies are exposed to in the womb may be important. However, this is currently a theory and even if it is found that early exposure to testosterone is important in explaining the gender difference, it does not rule out the importance of nature - because if could be that babies who later develop autism are more sensitive to the effects of testosterone in the womb. Other research involves looking at the sex chromosomes to see if differences there can account for the gender difference. Howevever, mothering patterns do not seem to be important with respect to the causes of autism.

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District of Columbia: What do you think about studies of adopted kids and adopted twins? Although the "nurture" part starts later, outside the womb, I remember reading tons of interesting stuff.

Biological siblings who grow up in different homes have more in common with each other than with the adopted siblings they grew up with. As part of an adopted family, it makes me sad, but I guess it makes sense.

Rob Stein: Yes, there's been a lot of research done on twins raised together and separately that have provided insights into the effects of genes versus the environment. Some of that research has indicated, like this study, that a genetic predisposition appears to be important. But most researchers do believe that it's not that simple, especially when it comes to complicated human behavior. Environmental factors probably do play a role, and it's the interaction between genes and environment.

Frances Rice: Yes, you both rightly say a lot of work has been done with adopted children. Much of it shows that inherited factors are important for behaviour but also that the interplay between inherited factors and the environment was important. So, for example one adoption study of antisocial behaviour showed that this kind of behaviour was most likely in children who had inherited a predisposition (their biological fathers had a criminal record) but they also grew up in an adopted family where there was some conflict.

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Princeton, N.J.: I had a friend who was a developmental Psychologist. She and her colleagues believed that the "simpler" a trait was, the more likely it was in heritable. So blue eyes - likely; intelligence (however you define it) - not so much. Is this still a viable theory

Rob Stein: It clearly does seem that more complicated behavioral traits are the result of a combination of genes and environment. Someone might inherit a gene or genes that, for example, might make them more prone to risky behavior. But that probably doesn't mean they will necessarily end up being jet pilots or being into extreme sports. It probably depends on how they are raised.

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Freising, Germany: Is there any solid scientific evidence that a woman can pass things like the taste for certain food to her baby during pregnancy?

Frances Rice: I'm not aware of solid scientific evidence that a mother can pass on preferences for certain foods to her baby during pregnancy. However, it does seem a possiblity that this might occur. Nevertheless, there are some nice studies looking at different aspects of babies learning in the womb. So for instance, babies are able to "learn" stories that their mothers read to them during late pregnancy - when tested after birth they prefer to listen to the story that their mother read to them rather than a new story. (As a scientific aside, experimental controls were used to make sure that this learning was not simply due to a preference for the mother's voice - it was not babies prefered the story their moms read to them in the womb even if it was later read in the experiment by a different woman i.e. not their mom). This kind of learning can happen because babies hearing is functioning before they are born. So, there is a different example of learning in the womb.

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One possible explanation might be that the donor eggs came from women with a genetic predisposition to antisocial behavior: OK, but then why did the other donor eggs that went to the smoking mothers not come from women with a genetic predisposition to antisocial behavior? This smells like a low N problem to me. Does this present a problem in interpreting the results? Frances?

Frances Rice: I think it is very unlikely that women who donated eggs had a genetic predisposition to antisocial behaviour for a couple of reasons. First, the average level of antisocial behaviour in the children of the related and unrelated mothers was in the normal range and the groups were not significantly different from each other. Second, participants were recruited from 19 UK clinics and 1 US clinic. In the UK, women are not paid for donating eggs and we only included donors who were unrelated to the mother. Therefore, our sample includes a very high proportion of women who donated eggs for alturistic reasons (and therefore these donors were unlikely to show antisocial behaviour). I should also note that donating eggs is not a physically comfortable experience and the fact that these women voluntarily did this to help an infertile couple realise their dream to have a baby strikes me as an alturistic act.

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Rob Stein: I read the story but...: as a non-scientist it's still unclear to me what the research has found. Can you sum up for me?

Rob Stein: Essentially the study found that children born to women who smoke while they are pregnant do not appear to be at increased risk for antisocial behavior because of any direct toxic effects of the smoking on the developing chid's brain, as had been suspected. Instead, it appears they are at increased risk for antisocial behavior because their mothers were more likely to engage in antisocial behavior. Hope that clarifies it.

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Anonymous: Aren't there lots of factors like the mother's age, diet, mental status, etc. that could skew the results ? How are these accounted for ?

Rob Stein: Yes, you're absolutely right. The researchers did try to account for as many of those kinds of variables as they could.

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Someone might inherit a gene or genes that, for example, might make them more prone to risky behavior. : But this is exactly the kind of idea my friend argued against. Being "prone to risky behavior" is much too complicated to be carried by a gene.

Frances Rice: I think you are getting at a couple of themes here. So first of all, it is quite widely accepted that complex behaviours (like risky behaviour) involve the effect of multiple environmental factors and multiple genes of small effect. That is, in terms of genes, the mode of inheritence involves many different genes each only having a small effect on the behaviour. Also, there can be indirect effects of genes (so called gene environment correlation and interaction). So, genes can work by influencing our behaviour which can then channel us into certain environments (e.g. risky environments) and also influencing our susceptiblity to certain kinds of environmental stressors. Suffice to say, understanding the origins of behaviour is certainly complicated and will involve the effects of many different influences.

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I read the story but...: as a non-scientist it's still unclear to me what the research has found. Can you sum up for me?

Rob Stein: Essentially the study found that children born to women who smoke while they are pregnant do not appear to be at increased risk for antisocial behavior because of any direct toxic effects of the smoking on the developing chid's brain, as had been suspected. Instead, it appears they are at increased risk for antisocial behavior because their mothers were more likely to engage in antisocial behavior. Hope that clarifies it.

Frances Rice: Hi there,

just to clarify that the association between smoking in pregnancy and antisocial behaviour in children is attributable to inherited characteristics (as opposed to toxic effects of cigarette smoke as previously thought). We controlled for maternal antisocial behaviour in our analysis so it could be that personality characteristics that the child inherits are important e.g. we all know how hard it is to give up smoking and there are neurobiological pathways involved so it could be that some kind of neurobiological influence is inherited by the child that increases antisocial behaviour. I just wanted to put this out there as an alternative interpretation of the results.

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Frances Rice: These results show that cigarette smoke reduces birth weight when mothers are related or unrelated to their babies but the results are different for antisocial behaviour in the children. We only see a correlation between smoking in pregnancy and child antisocial behaviour when women are related to their babies. This suggests that smoking in pregnancy does not affect children's later behaviour but that inherited factors are important in this relationship. We tried to control for important variables that might be important such as mother's stress in pregnancy, education levels and antisocial behaviour and found that these did not alter the pattern of results. Inherited characteristics that could be important include personality traits and also neurobiological functioning - we all know that it is difficult to quit smoking and there is a neurobiological basis to addiction, so it may be that this is inherited and influences children's behaviour.

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Maryland: "I think it is very unlikely that women who donated eggs had a genetic predisposition to antisocial behavior for a couple of reasons." OK, that seems likely. So let me ask again... why the elevated antisocial behavior in children of nonsmoking moms with donor eggs?

Frances Rice: It is elevated in the unrelated group but it is not statistically significant, therefore this seems to be just chance fluctuation. The levels of antisocial behaviour are within the normal range for both groups.

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Rob Stein: Well, our time is just about up. Thanks to everyone for your great questions. And thanks to Frances Rice for joining us today to discuss this fascinating research.

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