The poet and philosopher Lucretius followed Empedocles in his masterwork De rerum natura ( On the Nature of Things). Such proposals survived into Roman times. The proposal that one type of organism could descend from another type goes back to some of the first pre-Socratic Greek philosophers, such as Anaximander and Empedocles. In 1842, Charles Darwin penned his first sketch of On the Origin of Species. The existence of evolution is supported by empirical evidence and unanimously accepted by scientists, but has historically been the subject of non-scientific controversy and denial by some religious groups. Their discoveries have influenced not just the development of biology but numerous other scientific and industrial fields, including agriculture, medicine, and computer science. Evolutionary biologists have continued to study various aspects of evolution by forming and testing hypotheses as well as constructing theories based on evidence from the field or laboratory and on data generated by the methods of mathematical and theoretical biology.
In the early 20th century, other competing ideas of evolution such as mutationism and orthogenesis were refuted as the modern synthesis reconciled Darwinian evolution with classical genetics, which established adaptive evolution as being caused by natural selection acting on Mendelian genetic variation. The scientific theory of evolution by natural selection was conceived independently by Charles Darwin and Alfred Russel Wallace in the mid-19th century and was set out in detail in Darwin's book On the Origin of Species. Morphological and biochemical traits are more similar among species that share a more recent common ancestor, and can be used to reconstruct phylogenetic trees. Existing patterns of biodiversity have been shaped by repeated formations of new species ( speciation), changes within species ( anagenesis) and loss of species ( extinction) throughout the evolutionary history of life on Earth. The fossil record includes a progression from early biogenic graphite, to microbial mat fossils, to fossilised multicellular organisms. Thus, in successive generations members of a population are more likely to be replaced by the progenies of parents with favourable characteristics that have enabled them to survive and reproduce in their respective environments.Īll life on Earth shares a last universal common ancestor (LUCA) that lived approximately 3.5–3.8 billion years ago. This is followed by three observable facts about living organisms: (1) traits vary among individuals with respect to their morphology, physiology and behaviour ( phenotypic variation), (2) different traits confer different rates of survival and reproduction (differential fitness) and (3) traits can be passed from generation to generation ( heritability of fitness). Įvolution by natural selection was first demonstrated by the observation that more offspring are often produced than can possibly survive. It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms and molecules.
The evolutionary pressures that determine whether a characteristic should be common or rare within a population constantly change, resulting in the change in heritable characteristics arising over successive generations. Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on this variation, resulting in certain characteristics becoming more common or rare within a population. Different characteristics tend to exist within any given population as a result of mutation, genetic recombination and other sources of genetic variation. These characteristics are the expressions of genes that are passed on from parent to offspring during reproduction. Evolution is change in the heritable characteristics of biological populations over successive generations.
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