English naturalists Charles Darwin (1809-1882) and Alfred Russell Wallace (1823-1913), suggested that all species evolved from common ancestors through the process known as "natural selection". Darwin published the book "On the Origin of Species" in 1859 where he describes the process of natural selection as analogous to artificial selection with which humans have been selecting varieties of domesticated plants and animals.
Natural selection is the process by which favourable heritable traits become more common in successive generations of populations, while unfavourable heritable traits become less common due to differential reproduction in populations.