Dilnoza Muslimova: Birth rank – does it make a difference?

In Episode 11 of the DIAL Podcast, Dilnoza Muslimova from the Erasmus University in Rotterdam talks about birth rank, genes and how well children get on in life and whether and how parental investment matters. 

Birth rank, genes and later life outcomes was presented at the DIAL Mid Term Conference in June 2019 and is part of the NORFACE-funded project Gene-Environment Interplay in the Generation of Health and Education Inequalities. 


In Episode 11 of the DIAL Podcast, Dilnoza Muslimova from the Erasmus University in Rotterdam talks about birth rank, genes and how well children get on in life and whether and how parental investment matters.

Birth rank, genes and later life outcomes was presented at the DIAL Mid Term Conference in June 2019 and is part of the NORFACE-funded project Gene-Environment Interplay in the Generation of Health and Education Inequalities. 

Christine Garrington  0:00 

Welcome to DIAL, a podcast where we tune into evidence on inequality over the lifecourse. In today’s episode we’re talking about birth rank, genes and how well children get on in life. And whether and how parental investment matters. Our guest is Dilnoza Muslimova from the Erasmus University in Rotterdam, who is also a member of the DIAL research project Gene-Environment Interplay in the Generation of Health and Education Inequalities. She started by explaining the background to her research.

Dilnoza Muslimova 0:28

We’re very interested in how parental time investments interplay with the genetic endowment of children and how those parental time investments can overcome the genetic disadvantages that children have. So in that respect birth rank speaks a lot about the family environment. And yeah, it can be whether you have your older siblings, it can be whether I don’t know how much time your parents spent with you, or like, generally, what is the attention that you’re receiving, and we were taught that by the literature that talks a lot about parental time investment and the birth rank, couple of studies, they find that for example, children who are born later to the family.  They receive on average about 20 to 30 minutes less of parental time being at the same age as their older siblings. And we thought that it’s quite interesting to explore another study also finds this, that gap, siblings have in education and IQ, from the older sibling to the later sibling is almost half of this gap explained by parental time investments. 

Christine Garrington  1:36

Everybody’s interested in this whole sort of nature nurture debate I think but it’s really challenging to get information about or data about people’s genetics, and the life they lead. Where do you get your information from for this particular study that you’re doing?

Dilnoza Muslimova 1:52

We were quite lucky that we got funding and were obtaining access to several biobanks and biobank is basically the data storage of all the genetic information, and also biomarkers. Biomarkers are blood measures, and saliva measures, urine samples and so on. I have actually visited one myself in the Netherlands. It was very interesting to observe how they store it as biological samples for individuals at minus 80 degrees Celsius in the freezers, and some freezers are actually quite advanced enough to make it it’s quite exciting to see how people are very invested and want to obtain very much like evidence based research and have precise measures of your health and your genetic information.

Christine Garrington  2:42

And we’re talking about lots of people right? Lots of people.

Dilnoza Muslimova 2:44

Yeah, for the UK biobank that we’re using in our study it’s 500,000 people and it’s amazing because the larger the sample, the more precise, or more representative our results are. So yeah we’re quite lucky and another advantage of this biobank, is that they also survey people. In the same data set, you can find their health and genetic information but also their life outcomes; their income, their educational attainment and this allows a lot of prospects for research.

Christine Garrington  3:15

Like you say an incredible resource, incredible. So what aspects of participants’ genetic makeup, did you look at specifically? You have said some of the things that are available in the, in the biobank, what sorts of things do you look at and what were you able to tell from those?

Dilnoza Muslimova 3:31

When we talk about genetic endowments, it’s a bit tricky because it’s not like the whole genetic endowment that we look at. The saliva is collected from an individual, and then the genetic material in saliva is genotype, basically, your gene is coded 99% of the code is very similar to other people. It’s what makes us human. Like what gives us two legs, two arms and so on. And one percent is different, and it makes us more individual. We look at this 1% variation between individuals and their genome wide association studies, which try to analyse how this variation predicts life outcomes for example, education, IQ. There are very particular things like, I don’t know preference for tea. Yeah but we tried to focus on more established robust variants such as education and IQ, and the recent studies established that the variation explained by genes is almost the same as variation explained by income in education. So, it’s about 10 or 12% of variation in your outcome. We look at that specific aspect of the genetic information of an individual. 

Christine Garrington  4:45

So in simple terms, then what were you able to establish about birth ranks? So where brothers and sisters come in terms of order that they’re born, and what that meant for someone’s IQ level and educational attainment later on? Which is what you were keen to try to establish.

Dilnoza Muslimova 5:02

So aside of adding genetic information we established, we managed to replicate the earlier studies that show birth rank is negatively correlated with individuals’ IQ and individuals’ educational attainment, which is like the later you’re born, that lowers your education or IQ. But interestingly, there is no association between your genetic potential and birth rank. It means that a lot of variation, like a lot of causes are more environmental than genetic 

Christine Garrington  5:37

So it’s more to do with what happens after you are born in the family environment?

Dilnoza Muslimova 5:42

Exactly, yep because there is no difference in the potential between the siblings at conception. So that’s very interesting.

Christine Garrington  5:49

Yeah that’s a really important message isn’t it? And so tell us about some of the other key things that you’ve found so far?

Dilnoza Muslimova 5:55

Well the other finding that we find is basically that children who are disadvantaged genetically. So they have lower than average polygenic risk score recorded for education, or IQ, they’re more hampered by being born later. So, in other words, this finding translates into if we bridge it with parental time investments that it might be quite difficult for children with lower genetic endowment for education to catch up with their siblings, if they have lower parental investment. Basically what advantages about genes and birth they are both random within families. So, your genetic endowment is fixed at conception and it is randomly assigned based on your parental genes and your birth rank is also randomly assigned at your birth so you don’t choose your preference. It is not chosen by someone, it’s just a random. So when you look at the interaction of the birth rank and your genetic endowment .This is what we find that people who are weaker genetically, or who have lower genetic potential, if they were born later than they have even lower educational attainment or IQ, later in life. 

Christine Garrington  7:04

Now, it is important to be clear about what these findings don’t imply as much as what they do. So tell us first about how we should interpret them.

Dilnoza Muslimova 7:13

I think it’s very important to make clear that we do not mean that people who are born later are genetically disadvantaged. So it is very clear and this is one of the findings that we empirically confirm that they are not an genetically disadvantaged. Another thing that is also very important to make clear is that we do not mean genetic or environmental determinism – genes do not determine your whole life course. And at the same time environment does not determine all your lifecourse. It’s very complex interplay between the two. So you cannot, I think we do not propagate labelling people based on their genes or based on their family environment created.

Christine Garrington  7:57

Now its early days, I think that is another thing you are keen to stress, early days in the research, but what would you say that we’ve learned so far? Because it seems that you have found a lot already. And why is it important we really get to grips with it and understand it? Especially in this context of inequality and wanting to close the gaps between, you know those people who might struggle in life and those people advantaged in some way. 

Dilnoza Muslimova 8:22

I think what we learn from the study, is a lot of previous literature, talk about children’s endowments and how they interplay with the environment. But very few papers actually measured the endowments, and some of the measurements are mostly like birth weight. And birth weight is affected by prenatal parental investment so you don’t know what is causing what. And the advantage of our study is that both measures that we use are independent of each other and his allows us to measure the contribution of each aspect of nature and nurture. So that’s very interesting and very important. Yeah, and basically I underlined again what we found is that genetical disadvantage children are hampered even more great by fewer parental investments when it comes to their life long outcomes.

Christine Garrington  9:13

Birth rank, genes and later life outcomes is research presented at the DIAL midterm conference in June 2019 by Dilnoza Muslimova. You can find out more about the NORFACE funded DIAL projects at www.dynamicsofinequality.org. Thanks for listening to this episode of our podcast, which is presented and produced by Chris Garrington and edited by Elina Kilpi-Jakonen.