THAT'S THE WHY:The tallest person in modern history for whom there are reliable measurements was Robert Pershing Wadlow. From Illinois, he towered at eight feet 11 inches (2.72 metres) at the age of 22 in 1940 just before he died.

Earlier this year another record-holder died: He Pingping was two feet five inches (74cm) and was cited in the

Guinness Book of World Records

as the smallest man who could walk.

While extremes are rare and generally attributable to underlying disorders, there’s still usually a spectrum of heights among a roomful of human grown-ups.

But why? What makes us reach a particular level of tallness in early adulthood? Basically it’s down to a mix of genetics and environment.

Twin and sibling studies peg the genetic influence at about 80 per cent in Caucasians, while in African and Asian populations the heritability of height seems to be lower, at about 60-65 per cent.

Genome-wide association studies have already identified about 50 genes that contribute to height – and while the contributions of individual genes may be small, they combine to have a powerful effect.

But as in so many cases, while genes load the gun, environment pulls the trigger, and factors such as nutrition and sleep (when we release relatively high levels of growth hormone) at critical windows of growth also play roles.