Question: why is natural selection considered to be the mechanism for evolution

title: Natural selection
text: Natural selection is a cornerstone of modern biology . The concept , published by Darwin and Alfred Russel Wallace in a joint presentation of papers in 1858 , was elaborated in Darwin 's influential 1859 book On the Origin of Species by Means of Natural Selection , or the Preservation of Favoured Races in the Struggle for Life . He described natural selection as analogous to artificial selection , a process by which animals and plants with traits considered desirable by human breeders are systematically favoured for reproduction . The concept of natural selection originally developed in the absence of a valid theory of heredity ; at the time of Darwin 's writing , science had yet to develop modern theories of genetics . The union of traditional Darwinian evolution with subsequent discoveries in classical genetics formed the modern synthesis of the mid-20th century . The addition of molecular genetics has led to evolutionary developmental biology , which explains evolution at the molecular level . While genotypes can slowly change by random genetic drift , natural selection remains the primary explanation for adaptive evolution . 

Answer: answer: Darwin described natural selection as analogous to artificial selection, a process by which animals and plants with traits considered desirable by human breeders are systematically favoured for reproduction.  While genotypes can slowly change by random genetic drift, natural selection remains the primary explanation for adaptive evolution.