And the balance is shifting at an alarming rate. Only 40 years ago it would be the norm for mainly only tall parents to have tall offspring.
Now a large percentage of children are taller than both parents. I my opinion the growth hormones/elements they feed the animals we consume is at least partially responsible for this.
Historically, in Dundee, nutrition amongst the working classes was poor. Men were generally unemployed, and idled around street corners all day, with no exercise. But very many women got exercise through working in the jute mills. This resulted in a population of small thin men, and larger and heavier women, typified to perfection by Maw and Paw Broon in the comic section of Scotland's Sunday Post newspaper.
Its a combination of both. However, if both your parents and grandparents were dwarfs its highly unlikely that you will make it to six foot whatever you eat!