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Subject: Music

This US group was formed in Los Angeles, California, in 1978 by Steve Allen (guitar, vocals) and Ron Flynt (bass, vocals), two expatriate musicians from Tulsa, Oklahoma. Drummer Mike Gallo ...

Experimental Evolution

Experimental Evolution   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
3,999 words
Illustration(s):
1

...The first article provides a summary overview contrasting experimental and comparative/historical approaches for studying evolution; the second article provides a case study of an evolutionary experiment in which populations of E. coli have been propagated and monitored for 20,000 generations. For related discussions, see Adaptation ; Artificial Selection ; Bacteria and Archaea ; Comparative Method ; Fitness ; Genetic Drift ; Natural Selection ; and Senescence . An Overview Experimental evolution is a scientific method in which populations of...

Maternal-Fetal Conflict

Maternal-Fetal Conflict   Reference library

Encyclopedia of Evolution

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Subject Reference
Current Version:
2005

...to the fetus. Fetuses lacking a maternal genome but containing two paternal genome copies (complete hydatidiform moles, or CHMs) are particularly dangerous to the mother. CHMs exhibit a growth-without-form morphology similar to that of androgenetic mouse embryos, and carry a 15–20 percent risk of persistent trophoblastic tumor ( Tham and Ratnam , 1998 ). There seems little doubt that unrestrained expression of the fetal paternal genome is the cause of this disease. Preeclampsia. Preeclampsia is a relatively common complication of pregnancy characterized...

Plagues and Epidemics

Plagues and Epidemics   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...Justinian Egypt and Europe, a.d. 558–590 High fever, blackened swellings of lymph nodes called buboes in armpits and groin The bacterium Yersinia pestis Rats and rat fleas (bubonic form) Direct spread through the air from infected lung tissue (pneumonic form). Perhaps as many as 20 million people throughout Europe, unknown numbers in Africa and the Middle East. Black Death China in 1330s, Middle East and Europe, 1347–1350 " Y. pestis . Other possible causes, such as an outbreak of anthrax, are much less likely. " 25 million in Europe, 1/3 of the population...

Codon Usage Bias

Codon Usage Bias   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...Usage Bias Living organisms use 20 amino acids to construct their protein molecules. These amino acids are coded for by 64 codons of three nucleotides (e.g., the sequence TTT codes for phenylalanine). Almost all organisms use the same genetic code, which is referred to as the “universal code” (Table 1). Of the 20 amino acids, 18 are encoded by more than one codon. However, these synonymous codons (different codons that code for same amino acid) are not used uniformly; in almost every organism that has been studied, there are distinct preferences for...

Protein Folding

Protein Folding   Reference library

Encyclopedia of Evolution

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Subject Reference
Current Version:
2005

...interactions, the cell utilizes a set of special proteins known as chaperones that protect the nascent chains from forming nonnative complexes. Structure Although the total possible number of different amino acid sequences composed of the 20 protogenic amino acids is immense (for a chain of 150 amino acids long the number is 20 150 or approximately 10 195 ), and the number of possible three-dimensional conformations they can theoretically adopt is even greater, the total number of stable three-dimensional structures allowed by physics would appear to be...

Self-deception

Self-deception   Reference library

Encyclopedia of Evolution

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Current Version:
2005

...not well understood, we do know enough to question the common impression that information reaching our brain is immediately registered in consciousness, and that signals to initiate activity always originate in the conscious mind. While a nervous signal reaches the brain in only 20 milliseconds, it takes a full 500 milliseconds for the signal to register in consciousness. This is all the time in the world, so to speak, for emendations, changes, deletions, and enhancements to occur. Indeed, neurophysiologists have shown that stimuli can affect the content of...

Cell-Type Number and Complexity

Cell-Type Number and Complexity   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005

...“ Biological Complexity. ” Journal of Theoretical Biology 104 (1983): 7–20. McShea, D. W. “ Complexity and Evolution: What Everybody Knows. ” Biology and Philosophy 6 (1991): 303–324. Clear discussion of the concept of complexity in biology. Valentine, J. W. “ Two Genomic Paths to the Evolution of Complexity in Body plans. ” Paleobiology 26 (2000): 513–519. Valentine, J. W. , A. G. Collins , and C. P. Meyer . “ Morphological Complexity Increase in Metazoans. ” Paleobiology 20 (1994): 131–142. Traces rise in cell-type number through time. James W....

Convergent and Parallel Evolution

Convergent and Parallel Evolution   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
1,982 words
Illustration(s):
3

...to mere similarity owing to chance. At the molecular level, this distinction becomes very important because of the limited number of possible character states for nucleotides (one for each of the four nucleotides making up strands of DNA) and for amino acids (20 possible character states representing the 20 amino acids). The existence of convergent evolution in morphological, physiological, behavioral, and molecular changes indicates that there are significant constraints on the evolutionary process, and that these constraints are distributed across the...

Mammals

Mammals   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
5,871 words
Illustration(s):
1

...level seem to bear little resemblance to one another, yet certain features of the skeleton and dentition tie them into a single taxon. The armadillos, with their dorsal surfaces covered with a leathery skin embedded with dermal bone, present a distinctive appearance. There are 20 living species of armadillos, one of which reaches as far north as Oklahoma in the United States. Some species of armadillo are omnivorous, but others are specialized for feeding on ants and termites. The tree sloths are specialized for browsing on leaves in tropical forests. The...

Dinosaurs

Dinosaurs   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
3,672 words
Illustration(s):
2

...whose name means “birdlike foot,” is distinguished by elaborate dental modifications for grinding vegetation. Early members were small, about 1 to 2 meters (3–6 feet) in length, but some of the forms during the Cretaceous period (145–65 million years ago) reached nearly 20 meters (66 feet) length and as adults weighed several tons. Despite their suggestive name, ornithopod dinosaurs are not the ancestors of birds, and they became progressively less birdlike as time went on. The sister lineage of Ornithopoda is Marginocephalia, the “margin-headed”...

Malaria

Malaria   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
2,563 words
Illustration(s):
2

... et al., 1998 , 2000 ) as well as for mitochondrial genomes ( Conway et al., 2000 ). Based on these observations, the current distribution of P. falciparum throughout the world's tropical regions is believed to have derived from a small ancestral population within the past 20,000 to 60,000 years. Evidence exists to show that natural selection acts strongly on both the falciparum and its hosts. The human response is evident in the various hemoglobinopathies (e.g., sickle-cell trait) that have arisen to combat the Plasmodium . The P. falciparum ...

Environment of Evolutionary Adaptedness

Environment of Evolutionary Adaptedness   Reference library

Encyclopedia of Evolution

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Subject Reference
Current Version:
2005

...prior to the establishment of Homo sapiens , and over long periods of the past. However, few, if any, humans actually live under those conditions now. For example, at the time when the fossil evidence shows that the human brain was expanding (i.e., during the Pleistocene, between 2.0 and 0.2 million years ago), humans and their ancestors lived in very small scale societies, linked together by intimate webs of kinship, at low population densities, and with relatively little by way of technology. In contrast, the people who for the most part are studied by...

Owen, Richard

Owen, Richard   Reference library

Encyclopedia of Evolution

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Subject Reference
Current Version:
2005

...On Owen's large network of correspondents. Owen, R. The Life of Richard Owen . 2 vols. London, 1894. Thestandard Victorian “Life and Letters.” Richards, E. “ A Question of Property Rights: Richard Owen's Evolutionism Reassessed. ” British Journal for the History of Science 20 (1987): 129–171. A detailed account of Owen's evolutionism. Rupke, N. A. “ Richard Owen's Vertebrate Archetype. ” Isis 84(1993): 231–251. Discusses the scientific roots as well as the philosophical and political meaning of Owen's most famous contribution to the life sciences....

Stratigraphy

Stratigraphy   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
1,510 words
Illustration(s):
2

...developed in the early 1800s, no one could tell the age and duration of the different geological periods. Some geologists thought that the age of the earth was nearly infinite ( Hutton noted that there was “no vestige of a beginning”), but other scientists gave the earth only 20 million years or less for its entire history. The discovery of radioactivity in 1896 , however, provided the first method of obtaining a numerical age for geological events. When a radioactive atom, such as uranium or rubidium, spontaneously decays by nuclear reactions, it gives...

Character Displacement

Character Displacement   Reference library

Encyclopedia of Evolution

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Subject Reference
Current Version:
2005

..., D. Simberloff , E. Tchhernov , and Y. Yom-Tov . “ Feline Canines: Community Wide Character Displacement among the Small Cats of Israel. ” American Naturalist 136 (1990): 39–60. Fenchel, T. “ Character Displacement and Co-existence in Mud Snails (Hydrobiidae). ” Oecologia 20 (1975): 19–32. Grant, P. R. “ The Classic Case of Character Displacement. ” Evolutionary Biology 8 (1975): 237. Grant, P. R. Ecology and Evolution of Darwin's Finches . Princeton, 1986. Grudemo, J. , and K. Johannesson . “ Size of Mudsnails, Hydrobia ulvae (Pennant) and H....

DNA and RNA

DNA and RNA   Reference library

Encyclopedia of Evolution

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Subject Reference
Current Version:
2005

...or read by another, providing a simple means to transmit information. This elegant and straightforward principle underlies all heredity and evolution. DNA in genomes is complexed with protein and occurs in a tightly packaged form. The bacterial genome forms a dense nucleoid, about 20 percent protein by mass, but precise details of the interactions of the protein and DNA are not known. Eukaryotic DNA is contained in nuclear structures called chromosomes , in which a single unbroken double-stranded DNA molecule is complexed with proteins called histones and...

Fitness

Fitness   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
2,777 words
Illustration(s):
1

...are relevant to their final frequencies among the survivors. Second, the magnitude of the change in the frequencies of the two forms within a generation is determined by the magnitude of the difference in these relative values; for example, if v 1 / v 2 were only 1.1 instead of 2.0, the frequency of tolerants among the survivors would be 52 percent instead of 67 percent. To determine the new frequencies of the two forms among the next generation, which is necessary to describe the course of evolutionary change, we would also need to know their mode of...

Genetic Code

Genetic Code   Reference library

Encyclopedia of Evolution

Reference type:
Subject Reference
Current Version:
2005
Subject:
Science and technology, Life Sciences, Social sciences, Anthropology
Length:
3,000 words
Illustration(s):
2

...of Crick's closest colleagues). Because there are four possible bases in RNA (where DNA has adenine, guanine, cytosine, and thymine, RNA has adenine, guanine, cytosine, and uracil), there are 4 3 = 64 possible codons. However, because the genetic code specifies only 21 entities—20 amino acids and a “stop” signal—the genetic code is technically “degenerate” or redundant. That is, there is not a one-to-one correspondence between codons and amino acids. Instead, most amino acids are specified by more than one codon. Even before the general features of the code...

Homology

Homology   Reference library

Encyclopedia of Evolution

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Subject Reference
Current Version:
2005

...a Head. ” BioEssays 23 (2001): 8–11. Shubin, N. , and P. Alberch . “ A Morphogenetic Approach to the Origin and Basic Organization of the Tetrapod Limb. ” Evolutionary Biology 20 (1986): 319–387. Van Valen, L. “ Homology and Causes. ” Journal of Morphology 173 (1982): 305–312. Wagner, G. P. “ The Biological Homology Concept. ” Annual Review of Ecology and Systematics 20 (1989): 51–69. Günter P....

Mutualism

Mutualism   Reference library

Encyclopedia of Evolution

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Subject Reference
Current Version:
2005

...have been known for some time, it has only recently become recognized that there are substantial costs associated with these interactions as well. Most of these goods and services that organisms provide their mutualists involve some kind of initial investment. For example, up to 20 percent of a plant's total carbon budget can be allocated to support mycorrhizae, and over 40 percent of their total energy investment may be devoted to producing nectar for pollinators. Furthermore, mutualists themselves can inflict costly damage on their partners. For instance,...

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