When do we learn to be social?

Interesting video about the fascinating minds of babies and children.
One of the curious facts she mentions is that studies demonstrates that approximately a 18 month baby would give you what he/she thinks you like but a 15 month baby would give you always what the baby itself likes.

This means that at the age of 18 months babies learn that we don’t always want the same thing and they should do things to help other people get what they want.

Alison Gopnik: What do babies think?