The change in living things over long periods of time. Evolution is the change in inherited traits as a population of organisms passes through generations. Inherited traits encompass all levels of change, from changes in DNA sequences to life forms and social behaviors. The process of evolution has led to diversity at many levels. Not only the myriad of different species distributed on Earth, but also the diversity at the molecular level has been formed by the process of evolution.
What it means
Throughout the evolutionary history of life on Earth, biodiversity has increased through the process of speciation, in which one ancestral species differentiates into two or more descendant species. The evolutionary history of life on Earth can be revealed by analyzing traits such as morphology, biochemistry, behavior, DNA sequences, and fossils.
By comparing traits across species, it is possible to determine that species that diverged from the most recent common ancestor share many similar traits, and this principle can be used to construct a phylogenetic tree, a “tree of life”. Thus, a phylogeny is a representation of the evolutionary flexibility of species, and an extrapolation of the speciation process to current species or fossils.
The process of evolution can also lead to the disappearance of existing species, which is called extinction, and there have been several mass extinctions throughout Earth’s history where many species have disappeared at the same time.
Evolution is explained by two main processes: natural selection and genetic drift. Natural selection is the difference in survival and reproduction between individuals due to differences in phenotype. Natural selection allows a species to differentiate into new species over time in response to its environment.
Genetic drift is the process by which the frequency of alleles in a population changes over generations. Unlike natural selection, genetic drift explains that allele frequencies change because individuals passing on genes to the next generation are random.
History of evolutionary theory
In the 19th century and before, when Charles Darwin (1809-1882) lived, many people believed that species did not change. Influenced by religion, people believed that species were created and focused on finding characteristics and distinguishing between species. Carl Linnaeus (1707-1778), a Swedish surgeon and biologist, was the leading scholar of his time who believed that species did not change. On the other hand, French naturalist Jean-Baptiste Lamarck (1744-1829) argued that species change into new ones over time. Lamarck’s idea of speciation differed from Darwin’s and the modern view.
Lamarck believed that the lineage of a species is eternal and changes from one form to another, meaning that species do not branch off and do not go extinct. Lamarck argued that the traits acquired by an individual during its lifetime are passed on to the next generation, and that subsequent generations accumulate new traits based on those acquired by their ancestors, thus transforming species over time. Lamarck’s transformism, also known as the “dragon theory,” explains why giraffes have long necks as an example.
According to this theory, an ancestor of the giraffe lengthened its neck in order to reach the leaves high up in the tree, and in doing so, it gained a slightly longer neck, a trait that was passed on to its offspring, who in turn gained a longer neck than the ancestor, and after many generations, the current giraffe has a longer neck.
As a naturalist, Darwin traveled the world on the Beagle from 1832 to 1837. He realized that the finches he collected in the Galapagos Islands were different species on each island, and that flightless birds such as ostriches existed in South America, leading him to believe that species change over time. However, after observing that species are adapted to their environments and that there is variation among individuals, Darwin realized that Lamarck’s theory did not explain how species change.
Influenced by Thomas Robert Malthus’s (1766-1834) An Essay on the Principle of Population, Darwin began to explain evolution by noting that in animals and plants, as well as humans, when there are large numbers of individuals in a population, there is a struggle for existence among them. Darwin believed that under these conditions of competition for survival, variations that are relatively favorable for survival and reproduction will tend to be preserved, while those that are not will be lost.
Eventually, he argued, new species would emerge from this process over generations. Darwin called the process by which new species form in the natural world, or evolution, natural selection, in contrast to the artificially selected traits that livestock and crops carry from people. His theory of evolution by natural selection was published in 1859 as The Origin of Species by Means of Natural Selection or the Preservation of Favored Races in the Struggle for Life.
In the 1920s and 1930s, the theories of evolutionary theory were combined with population genetics, which focuses on Mendel’s laws of inheritance. The modern integration of evolutionary theory explains all aspects of biology, from developmental processes at the cellular level to changes in gene frequencies in populations to speciation.
Scholars such as Ronald Alymer Fisher (1890-1962), J. B. S. Haldane (1892-1964), Sewall Wright (1889-1988), Theodosius Dobzhansky (1900-1975), Julian Huxley (1887-1975), Ernst Mayr (1904-2005), and George G. Simpson (1902-1984) contributed to the development of biology in the 20th century. In its modern consolidation, modern biology incorporates all branches of genetics, morphology, phylogenetics, and paleontology into a unified explanation with evolutionary theory as its parent.
Dobzhansky’s statement that “nothing in biology can be properly explained unless it is viewed from an evolutionary perspective” emphasizes that even seemingly unrelated phenomena in biology can only be explained and predicted through an evolutionary interpretation.