Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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- A -

adaptive radiation
the relatively rapid expansion and diversification of an evolving group of organisms as they adapt to new ecological niches.  Adaptive radiation is the process by which one species evolves into two or more species.  This occurs as a result of different populations becoming reproductively isolated from each other, usually by adapting to different environments.
amino acids   click this icon to hear the preceding term pronounced
small molecules that are the components of proteins.  There are 20 different kinds of amino acids in living things.  Proteins are composed of different combinations of amino acids assembled in chain-like molecules.  Amino acids are primarily composed of carbon, oxygen, hydrogen, and nitrogen.
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- B -

binomial nomenclature  click this icon to hear the preceding term pronounced
in taxonomy, the convention established by Carolus Linnaeus whereby genus and species names are used to refer to species.  For example, Homo sapiens refers to human beings.  "Binomial" means two names in Latin.  The two names are also referred to as a "binomen".
biospecies  click this icon to hear the preceding term pronounced
a species that has been defined on the basis of the ability to produce fertile offspring.  Members of the same species can produce offspring that can in turn reproduce while members of different species cannot.  See morphospecies.

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- C -

catastrophism  click this icon to hear the preceding term pronounced
the view that the earth's geological landscape is the result of violent cataclysmic events.  Advocates of this theory usually believe that there have been a number of wide-spread violent and sudden natural catastrophes that have destroyed most living things.  This idea was used by George Cuvier to explain the extinction of species.   Catastrophism was opposed by uniformitarianism during the late 18th and 19th centuries.
codon  click this icon to hear the preceding term pronounced
a sequence of 3 nucleotide bases in a DNA molecule that codes for a specific type of amino acid to be assembled in the protein synthesis process.
creationism  click this icon to hear the preceding term pronounced
the belief that all species were created as they are today and that they have not undergone any evolution since then.  This view is usually based primarily on the Book of Genesis in the Judeo-Christian Bible.  Most creationists also believe that the earth is very young (typically about 6,000 years old).
chromosomes  click this icon to hear the preceding term pronounced
discrete, thread-like, gene-carrying structures in the cell nucleus. Chromosomes are composed primarily of DNA and protein.  Chromosomes are visible only under magnification during an early stage of cell division.

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- D -

deoxyribonucleic acid  click this icon to hear the preceding term pronounced
see DNA.
descent with modification
a phrase Charles Darwin used to refer to the process by which natural selection favors some variations resulting in their becoming more common in the next generation.  Descent with modification is another way of describing evolution.
DNA  click this icon to hear the preceding term pronounced     (deoxyribonucleic acid  click this icon to hear the preceding term pronounced)
relatively large, double-stranded molecules that contain an individual's genetic codes for the assembly of specific sequences of amino acids to make proteins.  The chromosomes in cell nuclei are mostly made up of DNA.

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- E -

ecological niches  click this icon to hear the preceding term pronounced
specific micro-habitats in nature to which populations or organisms adapt.   They are usually seen in terms of being food getting opportunities in the environment.
evolution   click this icon to hear the preceding term pronounced
genetic change in a population of organisms that occurs over time.  The term is also frequently used to refer to the appearance of a new species.

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- F - 

fossil  click this icon to hear the preceding term pronounced
any remains or traces of an ancient organism.   Examples of fossils are mineralized bones and casts and imprints of plants or animals.

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- G -

genetics  click this icon to hear the preceding term pronounced
the study of gene structure and action and the patterns of inheritance of traits from parent to offspring.  Genetic mechanisms are the underlying foundation for evolutionary change.  Genetics is the branch of science that deals with the inheritance of biological characteristics.
genus click this icon to hear the preceding term pronounced     (plural genera click this icon to hear the preceding term pronounced)
a group of closely related species.  In the Linnaean classification system, genus is the category immediately above species.
great chain of being
the theory that living things were divinely created and exist in an infinite and continuous series of forms, each one grading into the next, from simple to complex.  This view goes back to the ancient Greeks and was popular from the Middle Ages through the 18th century in Europe.

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- I - 

inheritance of acquired characteristics
Lamarck's theory that evolution occurs as a result of an organism acquiring a change in form due to using or not using particular body parts during its lifetime and then passing the new trait on to its offspring.  This is also referred to as the "use-disuse theory."

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- M -

marsupials  click this icon to hear the preceding term pronounced
the group of mammal species in which females bear their young in an immature condition (while still in the early fetal stage) and then permit their further infant development in an abdominal pouch covering their mammary glands.  Compared to the delayed births of placental mammals, this is inefficient in keeping young infants alive. Included in this infraclass are kangaroos, koalas, opossums, and many other species, especially from Australia and New Guinea.
morphospecies  click this icon to hear the preceding term pronounced
a species that has been defined on the basis of physical, measurable characteristics.  See biospecies.

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- N -

natural selection
an evolutionary mechanism that occurs when some individuals of a population are better able to adapt to their environment and, subsequently, produce more offspring.  Nature, in effect, selects which members of a population are fit to survive long enough to reproduce.  Differential reproductive success among individuals is the key.  Those who produce more offspring have a greater influence on the gene frequencies of the next generation.  This mechanism of evolutionary change was first described by Charles Darwin.
niches
see ecological niches.

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- P -

photosynthesis  click this icon to hear the preceding term pronounced
the process by which plants, algae, and some bacteria use energy from sunlight to create new organic molecules (specifically carbohydrates) out of carbon dioxide and water in specialized chlorophyll-containing cells.  Most forms of photosynthesis produce oxygen as a byproduct.
placental mammals  click this icon to hear the preceding term pronounced
the group of mammal species in which females produce a placenta to connect the fetus to the uterus.  This enables nutrients and oxygen to get to the fetus and provides a means of eliminating waste products.  As a result, placental mammals can carry their young within the uterus until late in fetal development.  This has a selective advantage because it results in decreased infant mortality.  Included in this group of species are dogs, cats, bears, whales, monkeys, humans, and many other animals
protozoa click this icon to hear the preceding term pronounced    (singular protozoan click this icon to hear the preceding term pronounced)
a group of single celled animal species.  Protozoa are classified as being members of the kingdom Protista.
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- R -

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- S -

sedimentary click this icon to hear the preceding term pronounced rock
rock formed from the build-up of sediments, such as those laid down by eroded rock and soil settling to the bottom of a slow-moving river or a lake.
special creation
the idea that all life forms were created by God as separate, distinct species.  The implication is that they do not change through time and that there is no evolutionary relationship between different species.  
species  pronounce word
the largest natural population of organisms that can potentially interbreed to produce fertile offspring.  It is commonly assumed that members of one species are reproductively isolated from members of all other species (i.e., they cannot mate with them to produce fertile offspring).  However, we must be cautious in defining species with this criterion because members of very closely related species can sometimes produce offspring together, and a small fraction of those may be fertile to some degree.  This is the case with mules, which are the product of mating between horses and donkeys.  About one out of 10,000 mules is fertile.  This suggests that some species differences are a matter of degree.
survival of the fittest
the idea that those individuals in a species that have characteristics selected for by nature are biologically the most fit.  They are the ones who more frequently survive to be the parents of the next generation.  The fittest individuals are not necessarily the strongest, largest, quickest, or smartest.  This concept was central to Charles Darwin's idea of natural selection.
synthetic theory of evolution  pronounce word
the 20th century conception of evolution being caused by a number of complex and often interacting processes.  This is essentially a combination of Darwin's concept of natural selection, Mendel's basic genetics, along with the facts and theories of population genetics and molecular biology discovered during the 20th century.

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- T -

taxonomy  click this icon to hear the preceding term pronounced
the branch of science concerned with the rules for naming, describing, and classification of organisms into different categories on the basis of evolutionary relationships.  The biological sciences primarily use the Linnaean classification system for this purpose.

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- U -

uniformitarianism  click this icon to hear the preceding term pronounced
the late 18th century theory of James Hutton that the natural forces now changing the shape of the earth's surface have been operating in the past much in the same way.  The most important implication is that the earth is very old and that the present is the key to understanding the past.  Elaborated on by Charles Lyell in the 19th century, this theory opposed catastrophism.
use-disuse theory
see inheritance of acquired characteristics.

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- V -

vertebrates   click this icon to hear the preceding term pronounced
members of the animal subphylum Vertebrata.  Vertebrates possess a spinal chord protected by a segmented vertebral column of cartilage and/or bone.

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Copyright 1998-2012 by Dennis O'Neil. All rights reserved.