Living things are filled with…stuff. We know this. But at what age did we start knowing this? Well, a study says it could be hardwired into our brains. Because infants seem to know that animals ought to have gushy insides, and not be hollow. The research is in the Proceedings of the National Academy of Sciences.

When babies see something ununusal they look at it longer than when they see the expected.

The researchers presented toys to 8-month olds that appeared to move on their own and also have an intention to move. They also showed the babies toys that could only do only one of these things, and toys that could do neither. The researchers then opened up the objects, all of which were hollow.

And the babies stared longer at the hollow toys that had appeared to move on their own with intention than they did at the other toys.

It appears that these hollow toys defied the babies’ expectations, as if they were thinking: There should be something in there. Which means babies make the mental link between intentional movement and the requirement for insides. They already know that this life takes guts.

—Christie Nicholson

[The above text is a transcript of this podcast.]