Evolution
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When used in a biological context, the word evolution refers to the change in the population of 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 are thought to have come 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 suited for survival and thus more likely to live long enough to pass on those genes to another generation.
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[edit] History
[edit] 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 developement.[1] Later, in Medieval times, Augustine used evolution as a basis for the philosophy of history.[2]
[edit] Origins of the theory
The first significant step in the theory of evolution was made by Carl Linnaeus.[3] His leading contribution to science was his creation of the binomial system of nomenclature - in layman's 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-Christan 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.
[edit] 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.[4] 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. [5] 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 onto his children.)
[edit] 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 some species had become extinct.[6] 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,[7] 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 in 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.[8] Darwin drew heavily on his knowledge of human experiments in breeding domestic animals, 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 of natural selection his books The Origin of Species and The Descent of Man.[9]
[edit] 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 male peacock.
[edit] Patterns in nature
The field of evolutionary biology seeks to provide explanations for four conspicuous patterns that are manifest in nature. The first three concern living species, whereas the fourth relates to fossils.
[edit] 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. [10]
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.
[edit] Adaptation
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.
[edit] Divergence
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.
[edit] 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.
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.
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.
[edit] Evidence for evolution
- See Common descent
[edit] Non-biological evolution
Evolutionary concepts can also be applied to non-biological processes. Universe formation and the development of languages are two 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. Languages can be seen as examples of memes, a word coined to mimic the biological "gene" in the sphere of ideas.
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.
[edit] Broad anti-evolution arguments
There are a number of broad arguments creationists/anti-evolutionists make. Specific claims are examined at our common descent page.
[edit] Random chance
Often creationists ask how likely it is that all this complex life could have come about by random chance. The claim, specific or implied, is that evolution is random. Evolution as a whole isn't random. Mutations are random, but the natural selection of specific genes or alleles is not. (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 helps with survival, then it is selected by means of the survival and reproduction of the individuals carrying that gene, if it is detrimental to survival it will not be selected due to the lower rate of survival and reproduction by individuals carrying the gene. Thus, there isn't anything random about natural selection.
Also, it's almost useless to talk about the probability of something happening after it has happened.
[edit] 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 always leads to the latter if given enough time to work. 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.
[edit] 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 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.
[edit] Falsifiability
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.
[edit] It's only a theory
Sometimes the phrase "evolution is only a theory" will be heard. this phrase rests on the common assumption that a theory is something that is possible but not proven. Science, however, defines theory as is 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, Which sets it at a higher level of reasoning. And if anyone says you can't directly observe evolution, send them to professor Lenski.
[edit] See also
- Acceptance of Evolution
- Cave man
- Common descent
- Disproving Evolution
- Evolutionary ethics
- Evolutionism
- Intelligent Design
- Natural selection
- Scientific evidence of evolution being a hoax, and God's existence
- Types of evolution
- Unguided evolution
- Young Earth Creationism
- Vandalism to this page
[edit] External links
[edit] 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
[edit] Sources
- Wile, Jay L. Exploring Creation With General Science. Anderson: Apologia Educational Ministries, Inc. 2000
- Understanding Evolution
[edit] References and notes
- ↑ Evolution from the Internet Encyclopedia of Philosophy
- ↑ ibid
- ↑ 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 [1] UC Berkeley
- ↑ See above.
- ↑ A brief account of how Wallace and Darwin both published on the Theory of Natural Selection
- ↑ The Descent of Man
- ↑ The Genetic Variation Program at the National Human Genome Research Institute
