Professor Luke O'Neill

Your body's under stress and they've hypothesized that that inflammation diverts nutrients away from the brain.

Because you're trying to fight the infection.

And therefore, maybe the brain is slightly different.

And again, that's a bit of speculation.

But it's not unreasonable to speculate that if you have an infection, something happens and maybe your brain develops slightly differently.

And as a result, then you don't do quite so well in exams.

And that might translate into poorer job prospects down the line is the idea.

So it's a complicated enough kind of notion, I suppose.

But I do like this idea that the second child is more likely to get infections.

And that could well then mean that certain things happen that mean they don't do as well in education.

And then they end up in a slightly worse job.

Now, the evidence again got even more compelling.

Why would the second child get more infections?

Well, it's very simple.

The older child goes to school or goes to the creche, brings back the infection that they've picked up with the other children.

And the infant or the young child, the second child then, is more likely to be infected because they've got a weaker immune system.

And this is well known.

When you're a baby, your immune system hasn't fully developed.

So if your older brother comes back from the school with an infection, you're more likely to pick it up and get really sick.

So that's the idea.