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Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life forms on Earth. Evolution holds that all species are related and gradually change over generations. [1] In a population, the genetic variations affect the phenotypes (physical characteristics) of an organism. These changes in the phenotypes will be an advantage to some organisms, which will then be passed on to their offspring. Some examples of evolution in species over many generations are the peppered moth and flightless birds. In the 1930s, the discipline of evolutionary biology emerged through what Julian Huxley called the modern synthesis of understanding, from previously unrelated fields of biological research, such as genetics and ecology, systematics, and paleontology.
The investigational range of current research has widened to encompass the genetic architecture of adaptation, molecular evolution, and the different forces that contribute to evolution, such as sexual selection, genetic drift, and biogeography. Moreover, the newer field of evolutionary developmental biology ("evo-devo") investigates how embryogenesis is controlled, thus yielding a wider synthesis that integrates developmental biology with the fields of study covered by the earlier evolutionary synthesis.
Evolution is the central unifying concept in biology. Biology can be divided into various ways. One way is by the level of biological organization, from molecular to cell, organism to population. Another way is by perceived taxonomic group, with fields such as zoology, botany, and microbiology, reflecting what was once seen as the major divisions of life. A third way is by approaches, such as field biology, theoretical biology, experimental evolution, and paleontology. These alternative ways of dividing up the subject have been combined with evolutionary biology to create subfields like evolutionary ecology and evolutionary developmental biology.
More recently, the merge between biological science and applied sciences gave birth to new fields that are extensions of evolutionary biology, including evolutionary robotics, engineering, [2] algorithms, [3] economics, [4] and architecture. [5] The basic mechanisms of evolution are applied directly or indirectly to come up with novel designs or solve problems that are difficult to solve otherwise. The research generated in these applied fields, contribute towards progress, especially from work on evolution in computer science and engineering fields such as mechanical engineering. [6]
Adaptive evolution [7] relates to evolutionary changes that happen due to the changes in the environment, this makes the organism suitable to its habitat. This change increases the chances of survival and reproduction of the organism (this can be referred to as an organism's fitness). For example, Darwin's Finches [8] on Galapagos island developed different shaped beaks in order to survive for a long time. Adaptive evolution can also be convergent evolution if two distantly related species live in similar environments facing similar pressures.
Convergent evolution is the process in which related or distantly related organisms evolve similar characteristics independently. This type of evolution creates analogous structures which have a similar function, structure, or form between the two species. For example, sharks and dolphins look alike but they are not related. Likewise, birds, flying insects, and bats all have the ability to fly, but they are not related to each other. These similar traits tend to evolve from having similar environmental pressures.
Divergent evolution is the process of speciation. This can happen in several ways:
The influence of two closely associated species is known as coevolution. [10] When two or more species evolve in company with each other, one species adapts to changes in other species. This type of evolution often happens in species that have symbiotic relationships. For example, predator-prey coevolution, this is the most common type of co-evolution. In this, the predator must evolve to become a more effective hunter because there is a selective pressure on the prey to steer clear of capture. The prey in turn need to develop better survival strategies. The Red Queen hypothesis is an example of predator-prey interations. The relationship between pollinating insects like bees and flowering plants, herbivores and plants, are also some common examples of diffuse or guild coevolution. [11]
The mechanisms of evolution focus mainly on mutation, genetic drift, gene flow, non-random mating, and natural selection.
Mutation: Mutation [12] is a change in the DNA sequence inside a gene or a chromosome of an organism. Most mutations are deleterious, or neutral; i.e. they can neither harm nor benefit, but can also be beneficial sometimes.
Genetic drift: Genetic drift [13] is a variational process, it happens as a result of the sampling errors from one generation to another generation where a random event that happens by chance in nature changes or influences allele frequency within a population. It has a much stronger effect on small populations than large ones.
Gene flow: Gene flow [14] is the transfer of genetic material from the gene pool of one population to another. In a population, migration occurs from one species to another, resulting in the change of allele frequency.
Natural selection: The survival and reproductive rate of a species depends on the adaptability of the species to their environment. This process is called natural selection. [15] Some species with certain traits in a population have higher survival and reproductive rate than others (fitness), and they pass on these genetic features to their offsprings.
In evolutionary developmental biology, scientists look at how the different processes in development play a role in how a specific organism reaches its current body plan. The genetic regulation of ontogeny and the phylogenetic process is what allows for this kind of understanding of biology to be possible. By looking at different processes during development, and going through the evolutionary tree, one can determine at which point a specific structure came about. For example, the three germ layers can be observed to not be present in cnidarians and ctenophores, which instead present in worms, being more or less developed depending on the kind of worm itself. Other structures like the development of Hox genes and sensory organs such as eyes can also be traced with this practice. [16] [17]
Phylogenetic Trees are representations of genetic lineage. They are figures that show how related species are to one another. They formed by analyzing the physical traits as well as the similarities of the DNA between species. Then by using a molecular clock scientists can estimate when the species diverged. An example of a phylogeny would be the tree of life.
Genes that have shared ancestry are homologs. If a speciation event occurs and one gene ends up in two different species the genes are now orthologous. If a gene is duplicated within the a singular species then it is a paralog. A molecular clock can be used to estimate when these events occurred. [18]
The idea of evolution by natural selection was proposed by Charles Darwin in 1859, but evolutionary biology, as an academic discipline in its own right, emerged during the period of the modern synthesis in the 1930s and 1940s. [19] It was not until the 1980s that many universities had departments of evolutionary biology. In the United States, many universities have created departments of molecular and cell biology or ecology and evolutionary biology, in place of the older departments of botany and zoology. Palaeontology is often grouped with earth science.
Microbiology too is becoming an evolutionary discipline now that microbial physiology and genomics are better understood. The quick generation time of bacteria and viruses such as bacteriophages makes it possible to explore evolutionary questions.
Many biologists have contributed to shaping the modern discipline of evolutionary biology. Theodosius Dobzhansky and E. B. Ford established an empirical research programme. Ronald Fisher, Sewall Wright, and J. B. S. Haldane created a sound theoretical framework. Ernst Mayr in systematics, George Gaylord Simpson in paleontology and G. Ledyard Stebbins in botany helped to form the modern synthesis. James Crow, [20] Richard Lewontin, [21] Dan Hartl, [22] Marcus Feldman, [23] [24] and Brian Charlesworth [25] trained a generation of evolutionary biologists.
Current research in evolutionary biology covers diverse topics and incorporates ideas from diverse areas, such as molecular genetics and computer science.
First, some fields of evolutionary research try to explain phenomena that were poorly accounted for in the modern evolutionary synthesis. These include speciation, [26] [27] the evolution of sexual reproduction, [28] [29] the evolution of cooperation, the evolution of ageing, [30] and evolvability. [31]
Second, some evolutionary biologists ask the most straightforward evolutionary question: "what happened and when?". This includes fields such as paleobiology, where paleobiologists and evolutionary biologists, including Thomas Halliday and Anjali Goswami, studied the evolution of early mammals going far back in time during the Mesozoic and Cenozoic eras (between 299 million to 12,000 years ago). [32] [33] Other fields related to generic exploration of evolution ("what happened and when?" ) include systematics and phylogenetics.
Third, the modern evolutionary synthesis was devised at a time when nobody understood the molecular basis of genes. Today, evolutionary biologists try to determine the genetic architecture of interesting evolutionary phenomena such as adaptation and speciation. They seek answers to questions such as how many genes are involved, how large are the effects of each gene, how interdependent are the effects of different genes, what do the genes do, and what changes happen to them (e.g., point mutations vs. gene duplication or even genome duplication). They try to reconcile the high heritability seen in twin studies with the difficulty in finding which genes are responsible for this heritability using genome-wide association studies. [34]
One challenge in studying genetic architecture is that the classical population genetics that catalysed the modern evolutionary synthesis must be updated to take into account modern molecular knowledge. This requires a great deal of mathematical development to relate DNA sequence data to evolutionary theory as part of a theory of molecular evolution. For example, biologists try to infer which genes have been under strong selection by detecting selective sweeps. [35]
Fourth, the modern evolutionary synthesis involved agreement about which forces contribute to evolution, but not about their relative importance. [36] Current research seeks to determine this. Evolutionary forces include natural selection, sexual selection, genetic drift, genetic draft, developmental constraints, mutation bias and biogeography.
This evolutionary approach is key to much current research in organismal biology and ecology, such as life history theory. Annotation of genes and their function relies heavily on comparative approaches. The field of evolutionary developmental biology ("evo-devo") investigates how developmental processes work, and compares them in different organisms to determine how they evolved.
Many physicians do not have enough background in evolutionary biology, making it difficult to use it in modern medicine. [37] However, there are efforts to gain a deeper understanding of disease through evolutionary medicine and to develop evolutionary therapies.
Evolution plays a role in resistance of drugs; for example, how HIV becomes resistant to medications and the body's immune system. The mutation of resistance of HIV is due to the natural selection of the survivors and their offspring. The few HIV that survive the immune system reproduced and had offspring that were also resistant to the immune system. [38] Drug resistance also causes many problems for patients such as a worsening sickness or the sickness can mutate into something that can no longer be cured with medication. Without the proper medicine, a sickness can be the death of a patient. If their body has resistance to a certain number of drugs, then the right medicine will be harder and harder to find. Not completing the prescribed full course of antibiotic is also an example of resistance that will cause the bacteria against which the antibiotic is being taken to evolve and continue to spread in the body. [39] When the full dosage of the medication does not enter the body and perform its proper job, the bacteria that survive the initial dosage will continue to reproduce. This can make for another bout of sickness later on that will be more difficult to cure because the bacteria involved will be resistant to the first medication used. Taking the full course of medicine that is prescribed is a vital step in avoiding antibiotic resistance.
Individuals with chronic illnesses, especially those that can recur throughout a lifetime, are at greater risk of antibiotic resistance than others. [40] This is because overuse of a drug or too high of a dosage can cause a patient's immune system to weaken and the illness will evolve and grow stronger. For example, cancer patients will need a stronger and stronger dosage of medication because of their low functioning immune system. [41]
Some scientific journals specialise exclusively in evolutionary biology as a whole, including the journals Evolution , Journal of Evolutionary Biology , and BMC Evolutionary Biology . Some journals cover sub-specialties within evolutionary biology, such as the journals Systematic Biology , Molecular Biology and Evolution and its sister journal Genome Biology and Evolution, and Cladistics .
Other journals combine aspects of evolutionary biology with other related fields. For example, Molecular Ecology , Proceedings of the Royal Society of London Series B , The American Naturalist and Theoretical Population Biology have overlap with ecology and other aspects of organismal biology. Overlap with ecology is also prominent in the review journals Trends in Ecology and Evolution and Annual Review of Ecology, Evolution, and Systematics . The journals Genetics and PLoS Genetics overlap with molecular genetics questions that are not obviously evolutionary in nature.
Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. The process of evolution has given rise to biodiversity at every level of biological organisation.
Microevolution is the change in allele frequencies that occurs over time within a population. This change is due to four different processes: mutation, selection, gene flow and genetic drift. This change happens over a relatively short amount of time compared to the changes termed macroevolution.
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection, which is intentional, whereas natural selection is not.
The modern synthesis was the early 20th-century synthesis of Charles Darwin's theory of evolution and Gregor Mendel's ideas on heredity into a joint mathematical framework. Julian Huxley coined the term in his 1942 book, Evolution: The Modern Synthesis. The synthesis combined the ideas of natural selection, Mendelian genetics, and population genetics. It also related the broad-scale macroevolution seen by palaeontologists to the small-scale microevolution of local populations.
Molecular evolution describes how inherited DNA and/or RNA change over evolutionary time, and the consequences of this for proteins and other components of cells and organisms. Molecular evolution is the basis of phylogenetic approaches to describing the tree of life. Molecular evolution overlaps with population genetics, especially on shorter timescales. Topics in molecular evolution include the origins of new genes, the genetic nature of complex traits, the genetic basis of adaptation and speciation, the evolution of development, and patterns and processes underlying genomic changes during evolution.
Population genetics is a subfield of genetics that deals with genetic differences within and among populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.
In biology, polymorphism is the occurrence of two or more clearly different morphs or forms, also referred to as alternative phenotypes, in the population of a species. To be classified as such, morphs must occupy the same habitat at the same time and belong to a panmictic population.
This is a list of topics in evolutionary biology.
Evolvability is defined as the capacity of a system for adaptive evolution. Evolvability is the ability of a population of organisms to not merely generate genetic diversity, but to generate adaptive genetic diversity, and thereby evolve through natural selection.
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the population during that process. Thirdly, it is a phenotypic trait or adaptive trait, with a functional role in each individual organism, that is maintained and has evolved through natural selection.
Genetics and the Origin of Species is a 1937 book by the Ukrainian-American evolutionary biologist Theodosius Dobzhansky. It is regarded as one of the most important works of modern synthesis and was one of the earliest. The book popularized the work of population genetics to other biologists and influenced their appreciation for the genetic basis of evolution. In his book, Dobzhansky applied the theoretical work of Sewall Wright (1889–1988) to the study of natural populations, allowing him to address evolutionary problems in a novel way during his time. Dobzhansky implements theories of mutation, natural selection, and speciation throughout his book to explain the habits of populations and the resulting effects on their genetic behavior. The book explains evolution in depth as a process over time that accounts for the diversity of all life on Earth. The study of evolution was present, but greatly neglected at the time. Dobzhansky illustrates that evolution regarding the origin and nature of species during this time in history was deemed mysterious, but had expanding potential for progress to be made in its field.
Neutral mutations are changes in DNA sequence that are neither beneficial nor detrimental to the ability of an organism to survive and reproduce. In population genetics, mutations in which natural selection does not affect the spread of the mutation in a species are termed neutral mutations. Neutral mutations that are inheritable and not linked to any genes under selection will be lost or will replace all other alleles of the gene. That loss or fixation of the gene proceeds based on random sampling known as genetic drift. A neutral mutation that is in linkage disequilibrium with other alleles that are under selection may proceed to loss or fixation via genetic hitchhiking and/or background selection.
The following outline is provided as an overview of and topical guide to genetics:
In biology, evolution is the process of change in all forms of life over generations, and evolutionary biology is the study of how evolution occurs. Biological populations evolve through genetic changes that correspond to changes in the organisms' observable traits. Genetic changes include mutations, which are caused by damage or replication errors in organisms' DNA. As the genetic variation of a population drifts randomly over generations, natural selection gradually leads traits to become more or less common based on the relative reproductive success of organisms with those traits.
Host–parasite coevolution is a special case of coevolution, where a host and a parasite continually adapt to each other. This can create an evolutionary arms race between them. A more benign possibility is of an evolutionary trade-off between transmission and virulence in the parasite, as if it kills its host too quickly, the parasite will not be able to reproduce either. Another theory, the Red Queen hypothesis, proposes that since both host and parasite have to keep on evolving to keep up with each other, and since sexual reproduction continually creates new combinations of genes, parasitism favours sexual reproduction in the host.
Evolutionary biology, in particular the understanding of how organisms evolve through natural selection, is an area of science with many practical applications. Creationists often claim that the theory of evolution lacks any practical applications; however, this claim has been refuted by scientists.
Evolving digital ecological networks are webs of interacting, self-replicating, and evolving computer programs that experience the same major ecological interactions as biological organisms. Despite being computational, these programs evolve quickly in an open-ended way, and starting from only one or two ancestral organisms, the formation of ecological networks can be observed in real-time by tracking interactions between the constantly evolving organism phenotypes. These phenotypes may be defined by combinations of logical computations that digital organisms perform and by expressed behaviors that have evolved. The types and outcomes of interactions between phenotypes are determined by task overlap for logic-defined phenotypes and by responses to encounters in the case of behavioral phenotypes. Biologists use these evolving networks to study active and fundamental topics within evolutionary ecology.
The following outline is provided as an overview of and topical guide to evolution:
The Extended Evolutionary Synthesis (EES) consists of a set of theoretical concepts argued to be more comprehensive than the earlier modern synthesis of evolutionary biology that took place between 1918 and 1942. The extended evolutionary synthesis was called for in the 1950s by C. H. Waddington, argued for on the basis of punctuated equilibrium by Stephen Jay Gould and Niles Eldredge in the 1980s, and was reconceptualized in 2007 by Massimo Pigliucci and Gerd B. Müller.
This glossary of genetics and evolutionary biology is a list of definitions of terms and concepts used in the study of genetics and evolutionary biology, as well as sub-disciplines and related fields, with an emphasis on classical genetics, quantitative genetics, population biology, phylogenetics, speciation, and systematics. It has been designed as a companion to Glossary of cellular and molecular biology, which contains many overlapping and related terms; other related glossaries include Glossary of biology and Glossary of ecology.