Professor Luke O'Neill

Whereas the older child didn't have that exposure.

They didn't have an older sibling to bring back the infection.

And that's why the risk of serious infections is higher.

in the second child than in the first.

So it all begins to add up in a very, very nice way.

Now, of course, they do discuss other reasons for this.

Why would the older child earn more?

And in the end, they reckon it's 50% roughly have to do with infection.

So in other words, this is a factor, an important factor in why ultimately the earning power is less in the second child.

The other things, though, have been already speculated upon, and they're probably reasonably robust.

The first is, if you're the older child, you get a lot more attention.

You're born, and the parents are wonderful because, oh, it's a new baby.

And you get a huge amount of attention, and that helps you develop in a different way.

Second child comes along, ah, okay, it's fine, you know.

less attention for the second child.

And that might be one reason.

So the older child is getting advantages in that way.

That's the first thing.

The second thing they talk about that's really interesting is very often the older child will teach the second child something.

It can be anything, but very often they show them how to play a game or whatever it might be.