Having ancestors that are too closely related may negatively influence an individual's height and thinking skills, a genetic study has shown

The effect of inheriting pairs of identical genes means children of first cousins are likely to be 1.2 centimeters (0.5 inches) shorter than those whose DNA is more mixed, scientists found. It was also predicted to have a significant impact on mental ability and educational attainment, as well as lung function. But surprisingly, factors such as blood pressure and cholesterol that influence the risk of heart disease, diabetes and other conditions were not affected by genetic diversity. The findings, based on genetic data of more than 300,000 individuals from around the world, suggest that natural selection is driving people to become cleverer and taller. In contrast, risk factors for complex diseases that occur late in life do not appear to be major players in the human evolutionary story.