When my daughters were younger, I remember getting them a secret agent kit. One of the activities in the kit was to build a cipher wheel, which basically consisted of a smaller disk and larger disk fastened together. In my daughters’ kit, both disks had the alphabet printed on them, but they could also contain numbers or symbols. Once  a cipher key was selected, for example, the letter 'O' on the inner disk might correspond to the letter 'J' on the outer disk, my daughters then had a pattern set up that allowed them encode and decode secret messages.

I am currently reading the book Sapiens: A Brief History of Humankind by Yuval Noah Harari. It's a great read on humanity and evolution. One interesting detail is that there were several different species of humans that lived on the earth. Eventually all other species disappeared. Homo sapiens won out in the end, but why?