Evolution takes place through natural selection, which was observed by Charles Darwin. Natural selection affects he genotypic make-up of the organsims, which basically control their phenotype. Effect of natural selection is different on all traits, and depends upon the organsim as well as environment. The environmental conditions affect the genetic make up and random mutations can occur in them, which might help them in surviving in a particular environment. In this case, only the mutated organisms will be able to thrive and populate further and hence are selected over others.
