| Part of the series on
“”[Evolution] is a general postulate to which all theories, all hypotheses, all systems must henceforward bow and which they must satisfy in order to be thinkable and true. Evolution is a light which illuminates all facts, a trajectory which all lines of thought must follow — this is what evolution is.
|—Pierre Teilhard de Chardin|
“”Evolution is a major thread in the larger tapestry that I like to call... REALITY.
Evolution refers to the change in a species' inherited traits from generation to generation. These traits are the expression, or "phenotype", of genes which, at least on earth, are stored in DNA. All species on earth came about by the mechanism of evolution. Evolution occurs as random genetic changes build up over time, and those that prove to be negative, or harmful, are weeded out as the organisms that have them are rendered less able to compete with the general population. Conversely, the organisms that had received beneficial alterations to their genes would be more likely to pass on those genes to successive generations, which may occur through increased survivorship, improved reproductive success, more abundant or viable offspring, or through other methods.
In a nutshell, evolution can be simplified to the following algorithm:
- A mutation occurs in an organisms' genes.
- If the mutation is useful (or effectively neutral), it survives and breeds, spreading the mutation.
- If it is not (e.g. a mammal being born without lungs), it doesn't survive or breed, and the mutation is not spread.
 Prehistory of evolution
The idea that life has evolved over time is not a recent one, and Charles Darwin did not, in fact, come up with the idea of evolution in general. For example, ancient Greek philosophers, like Aristotle, had ideas about biological development. Later, in Medieval times, Augustine used evolution as a basis for the philosophy of history.
 Origins of the theory
The first significant step in the theory of evolution was made by Carl Linnaeus. His leading contribution to science was his creation of the binomial system of nomenclature - in lay terms, the two part name given to species, such as Homo sapiens for humans. He, like other biologists of his time, believed in the fixity of the species, and in the scala naturae, or the scale of life. His ideas were consistent with the Judeo-Christian teachings of his time.
Erasmus Darwin, the grandfather of Charles Darwin, was the first scientist to whom credit can be given for something starting to approach modern concepts of evolution, as noted in his contributions to botany and zoology. His writings contained many comments (mostly in footnotes and side writings) that suggested his beliefs in common descent. He concluded that vestigial organs (such as the appendix in humans) are leftovers from previous generations. The elder Darwin, however, offered no mechanism by which he believed evolution could occur.
 Late eighteenth-century contributions
Georges Cuvier proposed a mechanism by which the fossil record could develop over time without evolution - which by now had come into usage as a term. His hypothesis, catastrophism, was that a series of disasters destroy all life within a limited area, and that living organisms move in to this newly opened area. This theory prefigures in some respects the modern theory of 'punctuated equilibrium'.
Lamarck was the first scientist to whom credit can be given for a theory of evolution. His belief centered mainly around use and disuse, and the hypothesis that the more an organism used a particular part of the body, the more developed it became within a species. His theory was sound only for individuals (e.g, a weightlifter will develop larger muscles over time, but will not pass this trait on to any children.)
 Natural selection
At this point in time, scientists had gathered a great deal of information on species, and knew life on Earth had been around for a long time and that some species had become extinct. Natural selection was the first theory to provide a mechanism for how evolution could work. Prior to the theory of natural selection, the concept that species changed over time existed, but there was no known mechanism for how that change occurred. Wallace and Darwin came to the conclusion, independently, that competition for resources and the struggle for survival helped determine which changes became permanent and which traits were discarded.
The theory of evolution by natural selection, as we know it today, was proposed in a joint paper by Alfred Russel Wallace and Charles Darwin on 20 August, 1858, based on Wallace's observations in the Malay Archipelago and Darwin's experiences on the HMS Beagle. Charles Lyell's Principles of Geology, which suggested slow changes over very long periods of time, also contributed to the nascent theory. Darwin drew heavily on his knowledge of human experiments in breeding domestic animals (artificial selection), particularly in the realm of variations produced in the breeding of pigeons, for his understanding of how variations can develop within a population over time. Darwin laid out his theory (actually, a hypothesis at the time) of natural selection in his books On the Origin of Species and The Descent of Man.
 Other forms of selection
Although natural selection was the first mechanism proposed in evolutionary theory (and remains the most common), other forms of selection play a part as well. The most notable of these is sexual selection, which occurs due to some heritable preference for a trait in breeding partners. Derivation of traits through this mechanism is driven by (usually) the female's choice in mating partner rather than direct impact on fitness. Sexual selection often leads to the rise of features which would likely not occur under natural selection, such as the tail of a peacock or the long necks of giraffes.
It should be noted that sexual selection can be divided into two forms, distinguishable by who actually "makes" mating decisions. The first of these is intersexual selection, and in this form of selection the limiting sex (which is usually female) will choose a partner. The other form is intrasexual selection, or mate competition. In this form of selection, one sex (usually males) competes for "mating rights" to members of the other sex.
 The eclipse of Darwinism
The eclipse of Darwinism is a phrase to describe the state of affairs prior to the modern synthesis when evolution was widely accepted in scientific circles but relatively few biologists believed that natural selection was its primary mechanism. Instead non-Darwinian mechanisms of evolution such as neo-Lamarckism, saltationism or orthogenesis were advocated. These mechanisms were included in most textbooks until the 1930's but were rejected by the neo-Darwinian synthesis theorists in the 1940's as evidence had proven the role of natural selection in evolution.
 Modern Synthesis
The modern evolutionary synthesis is a union of ideas from several biological specialties which attempts to explain how evolution proceeds. It has been accepted by many scientists. It is also referred to as the new synthesis, the evolutionary synthesis, the neo-Darwinian synthesis or the synthetic theory of evolution. The synthesis was produced between 1936 and 1947 due to the reconcilisation of Mendelian genetics with natural selection into a gradual framework of evolution. The synthesis of Darwinian natural selection (1859) and Mendelian inheritance (1865) is the cornerstone of neo-Darwinism.
Julian Huxley (1887 – 1975) invented the term, when he produced his book, Evolution: The Modern Synthesis (1942). Other major figures in the modern synthesis included R. A. Fisher (1890 - 1962), Theodosius Dobzhansky (1900 - 1975), Ernst Mayr (1904 - 2005), George Gaylord Simpson (1902 – 1984) and G. Ledyard Stebbins (1906 - 2000).
 Extended Evolutionary Synthesis
Over the past decade, new conceptions of evolutionary theory have emerged going under the umbrella term of the "Extended Synthesis," which is intended to modify the existing Modern Synthesis. This proposed extended synthesis incorporates new possibilities for integration and expansion in evolutionary theory, such as Evo-devo, Epigenetic Inheritance and Niche Construction. Its proponents include Massimo Pigliucci, Gerd Müller and Eva Jablonka. In 2008 sixteen scientists met at the Konrad Lorenz Institute in Altenberg, Austria to propose an extended synthesis.
 The principles of evolution
Evolutionary theory has at its core three main tenets, observations of patterns within nature. These three patterns were observed by both Darwin and Wallace, and they eventually gave rise to the modern theory.
 Natural variability
Darwin and Wallace both noted that populations always display variability in any particular trait. That is, among one population, some members may be very large, some may be very small, and most will usually be somewhere in the middle. Although early evolutionary scientists did not have the benefit of modern molecular tools, they surmised that the source of these variations must be some sort of heritable factor (in fact, one of the first predictions made by evolutionary theory was the existence of DNA!).
 Differential fitness
Having observed that natural variability exists, the early evolutionary biologists also noted that some of these variants endowed their possessor with some competitive edge over other members of the species. Although at first the implications of this fact were unclear, the writings of Thomas Malthus spurred Darwin and Wallace to propose that species produced more members than could survive. Thus, it would be only the members with the most competitive edge that would live and, presumably, reproduce.
 The "fittest" will produce more offspring
Backed by the idea of differential fitness and heritable variability, Darwin and Wallace independently came to the conclusion that those animals best suited to their environment would survive to produce more offspring, which would in turn be more competitive and produce more offspring than their rivals. Therefore, the heritable factor responsible (which we now know to be genes) would increase in frequency within the population until it had become the dominant versions of that trait.
 Patterns in nature
Evolutionary biology seeks to explain the following three broad patterns observable in all life.
 Genetic variation
According to the Genetic Variation Program arm, at the National Human Genome Research Institute, about 99.5% of human DNA is the same from person to person. The other 0.5% accounts for a number of simple and complex traits we possess.
There is tremendous genetic diversity within almost all species, including humans. No two individuals have an identical DNA sequence, with the exception of identical twins or clones. This genetic variation contributes to phenotypic variation - that is, diversity in the outward appearance and behavior of individuals of the same species.
Populations must adapt to their environment to survive.
Living organisms have morphological, biochemical, and behavioral features that make them well adapted for life in the environments in which they are usually found. For example, consider the hollow bones and feathers of birds that enable them to fly, or the cryptic coloration that allows many organisms to hide from their predators. These features may give the superficial appearance that organisms were designed by a creator (or engineer) to live in a particular environment. Evolutionary biology has demonstrated that adaptations arise through selection acting on a population through genetic variation.
Species evolved along different paths from a common ancestor.
All living species differ from one another. In some cases, these differences are subtle, while in other cases the differences are dramatic. Carl Linnaeus (1707-1778) proposed a classification that is still used today with slight changes. In the modern scheme, related species are grouped into genera, related genera into families, and so on. This hierarchical pattern of relationship produces a tree-like pattern, which implies a process of splitting and divergence from a common ancestor. While Linnaeus classified species using similar physical characteristics, modern evolutionary biologists also base classification on DNA analysis, which can distinguish between superficial resemblances between species and those which are due to common ancestry.
 Mechanisms of evolution
Biological evolution results from changes over time in the genetic constitution of species. The accumulation of genetic variations often, but not always, produces noticeable changes in the appearance or behavior of organisms. Evolution requires both the production of variation and the spread of some variants that replace others.
Offspring with genetic mutations are different from their parents.
- Genetic variation arises through two processes, mutation and recombination. Mutation occurs when DNA is imperfectly copied during replication, or by changes in genetic material caused by such mutagens as radiation, leading to a difference between a parent's gene and that of its offspring. Some mutations affect only one bit in the DNA; others produce rearrangements of, or changes in, large blocks of DNA.
Genes can be shuffled between organisms.
- Recombination occurs when genes from two parents are shuffled to produce an offspring, as happens in every instance of sexual reproduction. Usually the two parents belong to the same species, but sometimes (especially in bacteria) genes move between more distantly related organisms.
Not all mutations become fixed in a population.
- The fate of any particular genetic variant depends on two processes, drift and selection. Drift refers to random fluctuations in gene frequency, and its effects are usually seen at the level of DNA. Ten flips of a coin do not always (or even usually) produce exactly five heads and five tails; drift refers to the same statistical issue applied to the transmission of genetic variants across generations. Genetic drift is inverse to population size; that is, genetic drift has a greater effect on small populations than larger ones. For example, if a small part of a population becomes geographically isolated its members will develop new traits faster.
Natural selection guarantees that the fittest are most likely to pass on their genes.
- The principle of natural selection was discovered by Charles Darwin (1809-1882), and it is the process by which organisms become adapted to their environments. Selection occurs when some individual organisms have genes that encode physical or behavioral features that allow them to better harvest resources, avoid predators, reproduce successfully and such relative to other individuals that do not carry the same genes. The individuals that have more useful (adaptive) features will tend to leave more offspring than other individuals, so the responsible genes will become more common over time, leading the population as a whole to become better adapted.
Gene duplication allows for new genes to be added to a genome.
- Through a variety of mechanisms, gene duplication can occur which gives rise to two identical genes in the genome. Since only one of these genes is necessary, the other gene can undergo mutations without having an adverse effect on the original function of the gene. These duplicated genes called paralogs can give rise to protein families with similar yet distinctly different functions. For example the olfactory protein family consists of around 900 different smell receptors that all arose via gene duplication followed by unimpeded mutation.
Distinct species diverge from one ancestor and can no longer interbreed.
- The process that many people find most confusing about evolution is speciation, which is not a separate mechanism at all, but rather a consequence of the preceding mechanisms played out in time and space. Speciation occurs when a population changes sufficiently over time that it becomes convenient to refer to the early and late forms by different names. Speciation also occurs when one population splits into two distinct forms that can no longer interbreed. Reproductive isolation does not generally happen in one generation; it may require many thousands of generations when, for example, one part of a population becomes geographically separated from the rest and adapts to a new environment. Given time, it is inevitable that two populations that live apart will diverge by mutation, drift, and selection until eventually their genes are no longer compatible for successful reproduction.
- Working alongside with natural selection (death and survival pressure), spatial evolution is caused by individuals with random variation that are selected nonrandomly by how fast they travel away from home populations. The faster the individuals, the faster the individual she or he mates with, leading to fast offspring. This is both behavioral and morphological. The individuals 'race' their way to become a distinct species. Examples of Spatial evolution are new. For example, Australian researchers have detailed a new mechanism of evolution that is not based on natural selection but rather on how populations of organisms, such as cane toads, move around. 
 Evidence for evolution
- See Common descent
 Non-biological evolution
Evolutionary concepts can also be applied to non-biological processes. Evolutionary algorithms in computer science, universe formation and the development of languages are three such subjects. The study of etymology is one component of analyzing how languages have evolved, and parallels biological evolution, for example, in the way the same language diverges over time into two different languages when two populations that speak the same language become geographically isolated.
Another example of non-biological evolution is the evolution of technology and innovation, which, while being (mostly) intelligently-designed, is (mostly) not random. James Burke studied, authored books and hosted television programmes on the evolution of technology through a historical context.
Somewhat confusingly, the word "evolution" is also used in some sciences in a way that has no relation to the biological concept whatsoever. When an astronomer speaks of "stellar evolution", (s)he is taking about the changes that happen to a star over very long periods of time, as it progresses from gas cloud to protostar to main sequence star to post-main-sequence giant to stellar remnant. When a cosmologist speaks of "cosmic evolution", (s)he is talking about the changes in the size/shape/nature of the universe over time, sometimes on very long time scales, and sometimes at very brief time scales (such as fractions of a second after the Big Bang). Neither of these uses of the word "evolution" has anything to do with populations, heritable traits, selection criteria, descent, or any of the other hallmarks of "evolution" as the term is used in biology.
Creationists consequently confuse the biological and non-biological meanings of the word "evolution" and they claim that the Theory of Evolution includes the origin of the universe and the origin of life. The biological theory of evolution as proposed by Darwin and others has nothing to say about either the origin of the universe or the origin of life on Earth, though some biologists have extended the theory to the very beginning of life.
 Broad anti-evolution arguments
There are a number of broad arguments creationists/anti-evolutionists make. Specific claims are examined at our common descent page. They're mostly arguments born of a lack of understanding what evolution by mutation and natural selection actually is, though rarely they're advanced by more savvy creationists as direct misrepresentations and distortions of the theory of evolution.
 Random chance
Often creationists ask how likely it is that all this complex life could have come about by random chance. They suggest that since individual events, such as the abiogenetic formation of proteins, emergence of RNA, organization of unicellular into multicellular organisms, etc., are purportedly so highly improbable that the entire chain events culminating in the existence of even a single complex organism could not have happened as described. Therefore, God did it. As creationism is largely a program of negative apologetics (e.g. an attempt to show a claim that is viewed as contrary to Christian faith is internally inconsistent or irrational according to the Christian perspective), arguments such as this are in essence arguments from incredulity with the proponent denying a fact (in this case the statistical probability that such and such essential event will have occurred) in order to draw the unsupported conclusion that some other cause (the Christian God) was at work.
The implied argument that a God or "designer" was at work is itself fraught with more untenable problems. Putting aside that the illusion of design is itself problematic and assuming for the sake of argument that "design" is even identifiable in biological systems, if "random chance" is inadequate to account for some outcome, one is simply making unsupported assertions to contend that it is more probable that a designer was at work. If the causes are "designers" about which nothing is known, if they are capable of doing anything, if it is not known how or why they act, if it is not known when they acted (or will act), or if it is not known what they did (or did not, or could, or would), the causes are not enough to account for the results. If so, "design" in this sense is indistinguishable from random chance.
Nonetheless, evolution by natural selection isn't a random process. While genetic mutations may appear randomly, the natural selection of specific traits to produce a statistically significant allele frequency in a discrete population of organisms is highly deterministic. (An allele is a variation of a gene. For example the eye color gene has a blue allele, a brown allele, and other alleles.) If a gene aids survival with respect to any particular environmental stressor then it is selected by means of the survival and reproduction of the individuals carrying that gene and perpetuates in the population of organisms. If the trait is detrimental to survival, it will leave organisms vulnerable to a particular environmental stressor and through attrition lower the frequency of the allele(s) contributing to that trait in the subject population.
 Microevolution and macroevolution
Many creationists hold erroneous beliefs about evolution such as that which is expressed by the statement "I accept microevolution, but not macroevolution." (This is the position of YEC Kent Hovind.) Microevolution is supposed to be evolution that doesn't result in a new species and macroevolution is supposed to be evolution that does lead to a new species. This argument is akin to someone saying that while he believes that sometimes wind can erode rock, he doesn't believe it can change the rock's shape. Micro- and macroevolution describe the same process, but with a difference in operational time. If one accepts microevolution, they must also accept macroevolution, since the former inevitably leads to the latter if given a long enough time period and the separation of breeding isolates. One cannot simply accept one and not the other. In biology, macroevolution is a broad subject of which speciation is only one part. This argument against speciation may be an attempt by creationists to reserve the power to produce a species for God alone.
Some creationists have abandoned the attempt to deny that new species can appear (and disappear) by natural means, in favor of drawing a barrier, not between species, but between baramins (also known as "kinds"), some sort of collection larger than species. To date, there has not been given any indication of just what sort of a thing a baramin is, what is the nature of the barrier between baramins, or how one might detect the barrier (or suspect its non-existence) in any particular case, other than the uninformative "baramins are those things that present a barrier to evolution".
 Irreducible complexity
Irreducible complexity is a fancy name for Michael Behe's "watchmaker" argument. In a nutshell, irreducible complexity describes an organ (or other facet of a living thing) which the ideology's supporters claim could not have evolved in small gradual steps. It is claimed to be so complex that it cannot be reduced into other parts. In fact, every example of irreducible complexity Behe and others have come up with has been shown to not be irreducibly complex (for example, the incremental stages towards the "irreducibly complex" human eye that are found in the sight organs of other living organisms).
For any theory to be accepted as scientific it must be falsifiable. In other words it must be capable of making statements which could theoretically be disproved. Evolution's opponents claim that the theory of Evolution does not have this property, although this claim can be easily rejected. Theoretically, evolution could be falsified if scientists discovered an organism so complex and unique, with absolutely no explainable path as to how it could have evolved. Such an organism has not been found. Similarly—and ironically—there are the demands made by some creationists, that they be shown, say, a dog giving birth to a cat before they'll accept evolution. Such an event, if it occurred, would falsify (or at least strongly challenge) evolution, since speciation doesn't happen in a single generation and modern animals don't evolve into other modern animals.
 It's only a theory
Sometimes the phrase "evolution is only a theory" will be heard. This phrase rests on the common use of "theory" to mean what scientists call a "hypothesis," i.e., is something that is possible but not proven. Science, however, uses "theory" in a much different sense, namely as a testable model of the manner of interaction of a set of natural phenomena, capable of predicting future occurrences or observations of the same kind, and capable of being tested through experiment or observation. This sets it at a significantly higher level of reasoning than "wild and unproven guess", which is what is implied when this argument is mentioned. Note that creationists don't say that gravity is "only a theory." And if anyone says you can't directly observe evolution, send them to professor Lenski.
 Evolution is both a theory and a fact
Strictly speaking, evolution is something that happens in the world of life, and should be distinguished from a theory of evolution, which is (according to the above definition) a model of how evolution occurs. Thus evolution bears the same relationship with a theory of evolution as flight with a theory of flight, or sound with a theory of sound, or planetary motion with a theory of planetary motion. This is often expressed in the saying that "Evolution is both a theory and a fact", that is to say that the word "evolution" can refer not only to the process (the "something that happens"), but also to a fact that it is observed under such-and-such circumstances, and to a theory that is involved with the process ("how it happens", "what the consequences are of it happening").
 See also
- Acceptance of evolution
- Cave man
- Common descent
- Cataclysmic evolution
- Disproving Evolution
- Evolutionary ethics
- Intelligent Design
- Natural selection
- A Prescribed Evolutionary Hypothesis
- Project Steve
- Scientific evidence of evolution being a hoax
- Types of evolution
- Unguided evolution
- Vandalism to this page
- Young Earth Creationism
- Mistaken approaches to the question of evolution
- Religion and evolution
- Denis Noble
- Talk Origins Archive
- National Center for Science Education
- Fifteen answers to creationist nonsense
- Understanding Evolution
- Tree of Life web project
- Britannica Encyclopedia Evolution
 Historical writings
- Contributions to the theory of natural selection. A series of essays by Alfred Russel Wallace
- Darwinism (1889) by Alfred Russel Wallace
- The Decent of Man by Charles Darwin
- On the Origin of Species By Means of Natural Selection by Charles Darwin
 Other sources
- Wile, Jay L. Exploring Creation With General Science. Anderson: Apologia Educational Ministries, Inc. 2000
- ↑ Lewis Black on evolution
- ↑ 2.0 2.1 Evolution from the Internet Encyclopedia of Philosophy
- ↑ Brief history of Evolutionary Thought
- ↑ Biography of Georges Cuvier at UC Berkeley
- ↑ Biography of Jean-Baptiste Lamarck at UC Berkeley
- ↑ History of Natural Selection at  UC Berkeley
- ↑ See above.
- ↑ A brief account of how Wallace and Darwin both published on the Theory of Natural Selection
- ↑ The Descent of Man
- ↑ See Helena Cronin's The Ant and the Peacock. See also the controversy over the book: Paul E. Griffiths. The Cronin Controversy. The British Journal for the Philosophy of Science, vol. 46, no. 1, Mar. 1995, pp. 122-138.
- ↑ The Synthetic Theory of Evolution
- ↑ Massimo Pigliucci. An Extended Synthesis for Evolutionary Biology. The Year in Evolutionary Biology 2009: Ann. N.Y. Acad. Sci. 1168: 218–228 (2009).
- ↑ Biological theory: Postmodern evolution?
- ↑ note that the dominant trait does not replace other traits to the point of exclusion
- ↑ The Genetic Variation Program at the National Human Genome Research Institute
- ↑ Zimmer, Carl. Search for Genes Leads to Unexpected Places Deep Homology; New York Times
- ↑ Life Scientist - New mechanism of evolution uncovered
- ↑ PNAS - An evolutionary process that assembles phenotypes through space rather than through time
- ↑ By humans
- ↑ Cultural Evolution, Stanford Encyclopedia of Philosophy
- ↑ Richard Dawkins, The Selfish Gene
- ↑ Ussery, David (1997-2000). "A Biochemist's Response to 'The Biochemical Challenge to Evolution'." Center for Biological Sequence analysis.
- ↑ Evolution as Fact and Theory, Stephen Jay Gould
|Evolution Articles on RationalWiki|
|- Acceptance - Behe interview - Cladistics - Common descent: the incontrovertible evidence - Darwinism - De-evolution - Dinosaur - Disproving Intelligent Design - Disproving Evolution - Eugenics - EvoWiki - Evobabble - Evolutionist - Fossil record - Human - Macroevolution - Microevolution - Natural selection - Niche - Palaeos - Phylogeny - Signal detection theory - Social Darwinism - Stephen Jay Gould - Theory of Evolution - Wedge Document -|