Dr Emma Farrell

So it's not perfect, but it's a really well empirically supported measure of personality.

But one of the traits that's measured in this is conscientiousness.

And we know that as people get older, their conscientiousness tends to increase slightly.

So that gives the eldest child an unfair advantage.

They're always going to be more conscientious, by virtue of being older.

But the researchers were able to control for that.

And when they did, they didn't find any difference in conscientiousness amongst elder children and their younger siblings.

Yes, so there is some data to suggest that eldest children score just a teeny tiny amount of IQ points higher on IQ tests.

But before the eldest children start lighting up family WhatsApp groups all around the country, this is a tiny, tiny difference.

And it's thought to be down to all of that extra cognitive stimulation and attention that eldest children get.

And they are also more likely to teach their younger siblings.

So they've gotten really good at the tasks that we use, that IQ tests use as a proxy measure for intelligence.

But we know IQ tests are kind of a contested measure of intelligence and also shaped by things like parental expectations and education in ways that are far more influential than birth order.

So personality is a term we use to describe the relatively stable set of thoughts, feelings and behaviours that shape how we interact with the world.

So what makes you, you and me, me is a question that has really engaged the greatest minds for thousands of years.

If you go back to Socrates and Aristotle, they were really thinking about the role of nature and nurture and shaping who we are.

And psychology would say that personality is a combination of nature and nurture.

So it's somewhat inherited and it's somewhat shaped by our environment, our experiences, the resources and people we had around us as we navigate various life demands and challenges.

It's one of those big contested debates in psychology, the degree to which it's nature or nurture.

But I think we're pretty clear that birth order doesn't have very much to do with it.