Natural numbers only include zero if you define it so in the beginning of your book/paper/whatever. Otherwise it's ambiguous and you should be ashamed of yourself.

Natural numbers include zero

That is a divisive opinion and not actually a fact

Big naturals in fact include two zeroes:

(o ) ( o)

Spaces and parens added for clarity

Depends on how you draw it.

Strictly positive numbers, Z0^+^, don't include zero. Positive numbers aka naturals, Z^+^ = N, do.

Edit: this is what I've learned at school, but according to wikipedia the definitions of these vary quite a bit

Natural numbers include zero

Only if you're French or a computer scientist or something! No one else counts from zero.

There's nothing natural about zero. The famously organized and inventive Roman Empire did fine without it and it wasn't a popular concept in Europe until the early thirteenth century.

If zero were natural like 1, 2, 3, 4, then all cultures would have counted from zero, but they absolutely did not.