CID and intergenerational research
Sometimes the apple does fall far from the tree
Text: Dorine Schenk
Photos: Bram Belloni
All good things come in threes, or so the proverb goes. That is certainly true in this case: three passionate scientists from three different studies are conducting research on third-generation participants. Intergenerational research like this is essential to study the influence of genes and environment on behaviour.
Is your own upbringing a good predictor of how you parent?
Does like father, like son also apply to parenting? In other words, does the way you were raised play a role in the way you raise your own children? The answer appears to be ambiguous. Some people are very similar to their own parents in the way they raise their children, while others are not. Sanne Geeraerts (1988), researcher with the RADAR study in Utrecht, tries to explain these differences and bring this so-called intergenerational transmission of parenting into focus. It requires large datasets from long-term studies. That is why Sanne works on techniques and ways of combining existing studies.
‘In my research, I was initially interested in children’s behavioural control, i.e., the extent to which children can control themselves, control their emotions, and focus their attention on something,’ says Sanne. ‘This is related to all kinds of problematic behaviour.’ She focused mainly on children at first, but increasingly started to involve parents in her research as well.
Sanne shifted her focus to parenting and ended up with her current research. She looks at whether the way you were raised in the past predicts how you raise your children now. This requires long-term studies that map, on the one hand, how people were raised as children, and, on the other hand, how those same people raise their own children (often over 10 or 20 years later).
‘In Utrecht, we are studying this in the RADAR study,’ says Sanne. This study started in 2006 with nearly 700 teenagers. Over three-quarters of the original participants, who are now around 30 years old, are still participating. Some now have children of their own who also participate. As such, the study follows three generations.
‘Many people think that your own upbringing plays a big role in how you raise your children, but that relationship is generally not that strong at all.’
But how do you measure parenting? ‘You can observe parenting, for example, in a laboratory setting or in people’s homes,’ Sanne explains. You set up a task, such as cleaning up toys, and watch how parents and children deal with it. That is a fairly objective way of measuring, but it is also a snapshot that is artificial and filmed. At RADAR, researchers therefore also ask questions about parenting, to both parents and children. Sanne: ‘For example, we ask if parents raise their voices when their child disobeys.’
This provides interesting insights. For example, the researchers see a lot of variation between studies. In some, your own upbringing does seem to be a good predictor of how you parent and in others it is not.
‘Many people think that your own upbringing plays a big role in how you raise your children,’ says Sanne. ‘But what we have learned so far is that that relationship is generally not that strong at all. We do not know where the majority of these differences come from yet.’
Initial analyses show that parenting in early childhood may be a more important predictor than parenting later on. But studying this properly requires a large, diverse sample and they are scarce. That is why Sanne is trying to combine smaller, existing datasets. This is not easy, because these different studies are each set up with its own purpose. It is already a big step forward that the CID allowed third-generation participants from different Dutch studies to be measured in the same way. But ideally, you would like even more data, for example, from international studies as well.
‘I think that, in psychology, we can benefit a lot from techniques that combine existing datasets. Particularly developmental psychologists, as they often follow people for longer periods of time. These are expensive and time-consuming studies. Combining existing studies can help. I think there is a huge added value there.’
Sanne is now working in the United States for a year, at a research group with extensive experience in analytical methods to combine datasets from different studies. ‘Moreover, they have several long-term studies here with data that I can start combining with those of the RADAR study, among others.’
Does being bullied affect how you raise your children?
If you are badly bullied as a child or adolescent, how does that affect social relationships later in life, such as friendships? Does it make you less likely to trust people? Or do you enter relationships faster because you are happy that someone finally wants to spend time with you? Tina Kretschmer (1980) is trying to find answers to these questions within the TRAILS study in Groningen. For a few years now, she has also been looking at whether social experiences, such as bullying, get passed on to the next generation. ‘I think parents who have been bullied in the past pass on that experience to their children through protection or parenting behaviour.’
‘A few years ago, I had a conversation with a colleague about my research,’ says Tina. ‘I said that I wondered to what extent being bullied as a child or adolescent affects how you raise your own children. She told me that she was bullied badly and that now, when her four-year-old daughter goes to play at a friend’s house, she always makes her husband pick her up. She was unable to herself. She could not handle the possibility that her daughter would not fit in well in the group and she might be bullied as well.’
Five years ago, Tina received a grant to study whether being bullied affects the next generation. This project is part of the TRAILS study. Every few years, researchers collect information about the participants, in the form of interviews, questionnaires, tests, and sometimes physical measurements. Family members, school environment, and, in some cases, partners also provide information.
‘The TRAILS data is unique’
‘The TRAILS data is unique,’ says Tina. Thanks to the use of various research methods, much is known about the parenting and social development that the participants experienced over the past 20 years. Their experience of bullying was also documented in detail, by not only asking the children themselves if they bully or have been bullied, but the whole class. That, combined with genetic information from participants and their parents, makes it an enormously rich dataset.
The dataset provides a picture of the bullying history of the participants, who are now in their early 30s. To study its impact on the next generation, information is needed from TRAILS Next, a project that has been running since 2015 and follows the children of TRAILS participants. By now, there are several hundred of them. Tina: ‘It starts with a diary study during pregnancy, where future parents write down, for example, whether they feel anxious or happy. Once the child is born, a researcher will visit 3, 30, and 54 months after birth for interviews and measurements.’
When the child is 4.5 years old, they will also be asked questions. Because children at that age cannot yet fill in a questionnaire, the researcher uses hand puppets, Tina says. ‘One doll says, for example: I have lots of friends. The other says: I have no friends. And then they ask the child: and you? So, we collect data similar to questionnaire data.’
In late January, Tina was awarded another grant. ‘With that, we can continue the study and gather information when the participants are in their mid-thirties. We will look, for example, at whether there is a difference in social development between people with and without children. I am excited about this, because we hardly have any data on adult social development.’
Tina and her colleagues will also continue to collect data from the participants’ children. ‘I think that, in the coming years, we will learn a lot about how being bullied carries over into the next generation.’
Is dyslexia in the genes or does it come from the environment?
On average, children of highly educated parents score higher on the final placement exams in year 8 of primary school. ‘But you cannot conclude from that that this is only because of the parenting and homework support that they owe to their parents,’ says Elsje van Bergen (1981), researcher at the NTR in Amsterdam. ‘Parents not only provide their children with an environment, but they also pass on their genes.’ Elsje studies which environmental factors, such as parenting, affect children’s school performance. To distinguish these factors from the influence of genes, she also maps genetics.
As soon as Elsje discovered the world of science as a first-year student, she knew she wanted to become a scientist. With her broad interests, it was just a question of which field she would choose. After a flopped PhD in human movement science – ‘my supervisor, the research, and I were not a match’ – her perseverance led her to educational sciences at the University of Amsterdam. There, she did her PhD on research into children who are at an increased risk of dyslexia because one of their parents has it.
‘I became interested in why children with relatives with dyslexia are themselves at increased risk of this. Is it in the genes or does it come from the environment?’ says Elsje. That question led, via a few years as a scientist in Oxford, to the interdisciplinary research she does now. This focuses on the influence of genes and environment on differences between children in school skills, such as reading and maths. It brings together three disciplines: educational sciences, psychology, and behavioural genetics, i.e. the interplay of genes and environment in behaviour.
‘If the child is as similar to the mother as to the aunt in terms of, for example, numeracy, then it is passed on through the genes. If the child is more similar to the mother in this, then the environment she provided also has an influence.’
This research into cause and effect is not straightforward. ‘We know, for example, that children who are read to and have many books at home do better in school on average,’ Elsje says. ‘But you do not know if this is actually causal.’ It is also true that parents with dyslexia often enjoy reading less and have fewer books in the house. So, their children not only grow up with fewer books, but also with a genetic risk of dyslexia. ‘If such a child has dyslexia, you do not know whether it is due to the home environment, where there are few books, or due to their genes.’
Elsje studies the influence of environment and genes with, among others, data from the NTR. She looks at family ties, for example. Identical twins are known to share almost 100 per cent of DNA and fraternal twins 50 per cent, as do siblings and parents and children. ‘So, you can look at adult identical twins – they both have the same DNA – where one of the two has a child,’ Elsje explains. ‘If the child is as similar to the mother as to the aunt in terms of, for example, numeracy, then it is passed on through the genes. If the child is more similar to the mother in this, then the environment she provided also has an influence.’
In addition, scientists are also looking directly at DNA, for example, by looking at what part of their DNA parents pass on to their child. ‘We look to see if the untransmitted DNA predicts placement exam scores, because then it must be an environmental effect.’
Elsje: ‘From research where we looked at the placement exam scores of identical and fraternal twins, we know that 75 per cent of the differences between children come from genetic differences and about 25 per cent from environmental differences.’
Last year, Elsje received a grant with which she will study what factors in the home environment influence those differences in learning performance. She will do this through genetic research, questionnaires for both parents and teachers, and with online language and maths games that allow researchers to see how much children are practising and learning.
By discerning which genetic and which environmental factors cause educational disadvantages, Elsje hopes to understand ways to reduce opportunity inequality in education. ‘DNA is not going to change, but you can optimise environment.’
Sanne Geeraerts is assistant professor at Universiteit Utrecht. Tina Kretschmer is professor at Groningen University. Elsje van Bergen is associate professor at the VU in Amsterdam.
This article is part of a New Scientist special issue about the Consortium on Individual Development, that will appear in September 2023.
