Memes

I think it's fair to say every kid likes to take credit for something they were shown by a grown up that they find out other kids don't know yet.

There's always that one young kid that made up a joke that everyone over the age of 10 has already heard.

Could be true though. Many symbols, e.g. the swastika, appeared in different cultures all over the world.

Because population is growing, it kind of makes sense that the same thing is discovered independently more often. There might also be a connection to the use of checkered paper in schools which makes some symbols more probable if you just draw along the lines.