More individuals are produced each generation that can survive. Phenotypic variation exists among individuals and the variation is heritable. Those individuals with heritable traits better suited to the environment will survive.Charles Darwin's theory of evolution states that evolution happens by natural selection. Individuals in a species show variation in physical characteristics. ... As a consequence those individuals most suited to their environment survive and, given enough time, the species will gradually evolve.
An aloe vera plant possessing a trait for extra thick leaves survives very long droughts in deserts, while and aloe vera plant that doesn't have thick leaves doesn't.
