How Tall Will an Athlete Grow?

Growing Up on the Volleyball Team

1Esme Lachance is a sixth grader on her school's volleyball team. Her teammates often joke about who will end up the tallest. For a science project, Esme asked the school nurse, Mr. Arturo Vélez, how scientists study what makes people grow tall. He showed her two kinds of data, with the numbers rounded.

2The first kind comes from twin studies. Identical twins come from one fertilized egg that splits, so they share almost all of their genes. Fraternal twins come from two different eggs, so they share about half of their genes, like any brother and sister. In one study, scientists measured the adult heights of 60 identical and 60 fraternal pairs of same-sex twins. Every pair had grown up together in the same home, so the two twins in a pair were raised at the same time, by the same family, eating similar meals. For comparison, they also measured 60 pairs of unrelated adults of the same sex, picked at random from the same towns.

3The second kind of data comes from one country's school health checkups, where nurses have measured children every year for about a century. Over that time, food in the country became more plentiful and varied, and far fewer children had long, serious illnesses. Mr. Vélez pointed out that the genes of a large population change very little over just a few generations. He added that the body releases much of its growth hormone during deep sleep.

4Esme also measured her own team. The 12 players were, on average, 6 cm taller than the average student in their grade. Esme wondered what the data could and could not tell her about why.