"Number" is at the foundation of
Mathematics. It's what we use to represent things we
count. The original idea covers the
natural numbers (=1,2,3,...), and then extends to
zero,
negative numbers, and off into lots of complication.
There has been some
research that suggests that
humans have an innate number sense. The research involved presenting babies with situations which obeyed
preservation of number, and comparing their reaction to when they saw situations which violated this.
For example, they would be shown a screen, and shown that nothing was behind it. Then, they would see one hand put a doll behind the screen. When the screen was removed, there would be two dolls there. In that case, even babies less than 1 year old acted more surprised than when there was the expected number of dolls there. (The way you tell reactions of someone who can't talk is by looking at their eyes - babies look at unexpected things longer than they look at expected things.
It makes sense that there would be at least a basic genetically programmed ability to use numbers - like
language, numbers are useful for many social interactions.