the variability hypothesis, also known as the greater male variability hypothesis, states that males display greater variability in traits than females do. it has often been discussed in relation to cognitive ability, where it has been observed that human males are more likely than females to have either very high or very low intelligence. the sex-difference in the variability of intelligence has been discussed since at least charles darwin. sex-differences in variability are present in many abilities and traits — including physical, psychological and genetic ones. it is not only found in humans but in other sexually dimorphic species as well.