For instance, A study was done on an amazonian tribe where a line was drawn and 1 rock was put on one side of the line and 9 rocks were put on the other. When asked what number of rocks would lie between these two most of us would say 5 but they all said 3. This is because they never learned to think of numbers in anyway other than ratios and 1 * 3 and 3*3 = 9 therefore 3 is the middle number. And other studies corroborate that we have this sort of thinking as early as 3 months old.
Edit2: I have been told integers should be replaced with linear. I'm not a mathematician I just play one on PC.