Charles [?] was one of the first people to explain the mechanism of evolution. He recognised that all offspring produce [?] offspring than can survive. He also noted that the offspring showed [?] , either bought about by [?] reproduction, or by a [?] . This meant not all the offspring would be equally well to their environment, so some would be able to outcompete others at staying alive. Because their ability to survive has been determined by natural pressures such as temperature, [?] or the efficiency of , this pressure on survival is called Selection.
Darwin realized that if adaptations had a genetic basis (ie. were controlled by [?]), then the offspring of survivors would these beneficial genes. The offspring would therefore also be at an advantage - PROVIDED THE CONDITIONS REMAINED THE . Clearly the poorly adapted individuals died and did not pass on their genes, the gene pool therefore evolves to contain more beneficial genes. Evolution therefore relies on the death/ [?] of less adapted organims.