Genetic differences, painstakingly crafted by thousands of years of natural selection, explain why Europeans from the north tower over their southern cousins, researchers said. In a study that touched on the age-old “nature vs nurture” debate, an international team of scientists set out to determine once and for all why, for example, the average Dutchman’s frame differs so much from that of, say, a Portuguese person. “We found that genetic differences between countries provides an explanation for national differences in height,” lead author Matthew Robinson, from the University of Queensland in Australia, said Monday. Many physical traits, including height and body mass index (BMI: a ratio of height to weight), vary between people from different regions of the world, even different parts of the same continent. In Europe, for example, the Dutch are seven centimetres taller on average than Italians, and rise eight centimetres above Spaniards. But the relative contribution of genes and environmental factors has never been clear. “We were interested in working out whether there were genetic differences,” said Robinson. The team used genetic data from 9,416 Europeans from 14 countries to predict their height and BMI. They then checked the predictions for national differences, which would indicate that the genes influencing height and BMI were more or less prevalent in people from different countries. “They found that historic natural selection on both height and BMI has created genetic differences among different countries,” said a Nature press summary. The association was stronger for height than for mass - about a quarter of the variation in height and eight percent of the variation in BMI could be explained by regional genetic characteristics, the team found. The cause was likely “historic natural selection” - the Darwinian process whereby humans or animals best suited to their environment survive and transmit their genetic traits to succeeding generations, whereas inferior traits disappear over time. “Many thousands of years ago when Europe was being settled, it is likely that the characteristics that were best to survive differed in the Mediterranean as compared to northern Europe,” Robinson theorised. The team also found that tall nations such as the Netherlands and Sweden were genetically more likely to be slim, though BMI was more strongly influenced by environmental factors than height.