 While upper body strength is on average more sexually dimorphic in humans than in most other primates except gorillas, there is fossil evidence that male upper body strength and muscular sexual dimorphism in the upper body during human evolution peaked in Homo erectus and decreased along with overall robustness during the evolution of Homo sapiens with its neotenic traits.The fact that Homo sapiens survived while archaic human species that retained erectus-like sexual dimorphism in upper body strength died out contradicts the interpretation that enhanced chance of the species to survive makes taxa with high sexual dimorphism more species-rich on average, but can be explained by the theory that rampant sexual selection cause rapid speciation at the expense of genetic variation within species.This theory holds that strong sexual selection separate populations to little or no interbreeding so that new species are formed, but also homogenize each population/species by unforgiving sexual selection against differences from a "species norm" which makes the species more adapted to its specific environment but decreases the chance of some individuals of the species surviving environmental change.