Darwin's ideas about organic evolution were drawn from existing forces of knowledge about evolution developed by Lyell, Malthus, and Lamarck. Although Darwin was not the first to think of the concept of evolution, he was a revolutionary in developing a coherent theory of evolution. The distinctive element of Darwin's evolutionary theory is the way he viewed species. Darwin considered variation among individuals of a species to be natural. He further argued that variation, far from being problematic, actually provides the explanation for the existence of distinct species. Darwin adopted elements of Malthus's theory of population growth and stated that only those members of a population survive who are able to adapt through variation. Therefore, over generations, adaptive variations will accumulate in the population and this will result in constant variations within species over time. According to Darwin, species are non-static and progressive in nature. Darwin's view of species was very different from that of his contemporaries. Rather than defining species in idealistic terms that implied the rejection of deviations and differences within species, Darwin viewed species as continually evolving. Carolus Linnaeus classified organisms based on their degree of similarity. Linnaeus believed that each species existed in an ideal form. He considered the variations problematic and imperfect. Darwin on the other hand believed a lot in the idea of ​​materialism and applied it to his idea of ​​evolution. Darwin's view on species also differed from Lamarck's. Although Lamarck argued that species change over time, it is important to point out that his theory of transformation was different from that of Darwin and the modern theory of... half of paper... ...at birth and with high growth of the postnatal brain. When we look at life history variations among Primates, unlike other Primates, humans have a longer period of infantile dependence, human infants, in natural fertility societies, are weaned much earlier than any great ape: Chimpanzees and orangutans wean, on average, at about 5 and 7.7 years, respectively, while humans wean, on average, at about 2.5 years. It is argued here that the neurological basis of human intellectual ability cannot be sustained for much longer than a year by breast milk alone, and therefore early weaning, when accompanied by supplementation with more nutritious adult foods, is vital to l ontogeny of our largest brain. .• Life history variations in primates, Paul H. Harvey and T. H. Clutton-Brock, Evolution, vol. 39, no. 3 (May 1985), pp. 559-581• http://www.primates.com/primate/index.html