It is to do both with how tall your family are (genetics) and also to do with the environment you live in (amount of food you eat, whether you were sick as a child etc…)
The DNA you get from your parents has a set of instructions for how you are built. Unfortunately for me both my parents were short(ish) so I am very short as I got an instruction from each parent giving some information about my height. It isn’t as simple as that though as some people can be shorter becasue they didn’t eat enough or they may not produce enough growth hormone.
There is always variation in a population and this can be due to a number of reasons!! As kimberley said your DNA, medical history and environment are all factors to consider. Some people have achoondroplasia (are dwarves) because they have mutations in a single gene in their DNA called the FGFR3 gene which is involved in bone growth!
Hi rachelbow! Kimberley and Amy are right on! It is a combination of genetic and environmental factors. We inherit a lot of our characteristics from our parents in our genes. But upbringing definitely plays a role too – as Kimberley has said healthy food can help you achieve your maximum height (dictated by your genetic make-up).
So why are people different then? Well, diversity in a population is really good for evolution. It means that we have many more kinds of situations we can adapt to as a population. For example, giraffes didn’t start out being super tall with super long necks – but there was a gradual trend over many generations to lengthening neck size because those members of the population with longer necks survived! In another situation, say if food was abundant on the ground, giraffes with shorter necks may have more readily survived.
Same thing with humans, the environment selects for specific height ranges. In some populations people are on average very small. This tends to be true in tropical climates, where metabolism need to be fast and efficient. In colder climates people tend to be larger since they need to be big to stay warm. There are always variations within a population though. And, nowadays we have become so integrated in our populations, with people moving all over the globe, some of these height differences are pretty noticeable!!