Though we can’t really know for sure, it’s thought that humans have had counted and had a concept of numbers for up to 50,000 years. Interestingly, we had a vast concept of time before numeracy.

The reasons why early man began counting were fairly similar to the reasons we need to count today. How many people are in my tribe compared to their tribe, etc. Many animals in fact can count and have an impressive concept of basic numeracy. Lions, for example, are known to count the number of lions in an opposing coalition and generally avoid conflict if they are outnumbered.

However, the ability to count and widespread understanding of the verbal and illustrative labels attached to numbers are very different. I believe that we first started to see widespread in depth, labelled counting systems around 12,000 years ago, when man changed from hunter-gatherer to farmer. It was important for tribes and farm workers to be able to communicate exactly how many cows were in a field or how many buckets of grain they have harvested, for example.

Naturally, our need for increasingly large numbers was constant, but for the number 100 specifically, base 10 counting systems didn’t really pop up until the 7th century. Before this, base 60 was the most widespread numerical system (and this is still seen today - most people use base 60 for timekeeping, for example).

So in short, we developed the need to count at least 50,000 years ago, we started applying names to them at least 12,000 years ago, and we the number 100 was created about 1,400 years ago.