This document discusses Charles Darwin and his theory of evolution by natural selection. It explains that Darwin was a naturalist who studied species on his voyage on the Beagle. Upon returning, he wrote On the Origin of Species, in which he proposed that (1) populations have more offspring than can survive, (2) there is variation within populations, and (3) individuals with traits better suited to their environment are more likely to survive and reproduce, passing on those traits. Over generations, this process of natural selection leads to adaptation and evolution of species. The document addresses common misconceptions and provides examples of natural selection in gazelles and peacocks.