of the term evolution:
Evolution is any change in the combined genetic material in a POPULATION, i.e., by definition, evolution has occurred if there is any change in the POPULATION'S gene pool. Especially note that individuals do not evolve - populations evolve.
Evolution can easily be observed to occur WITHIN a species over time.
Darwin extended the concept to propose that, due to many different
selection pressures caused by changing environments over a long period of time,
enough changes in the genetic material could occur in a population over time
that could result in the creation of a NEW SPECIES. A species is defined as a group of similar organisms that
share many characteristics, INTERBREED IN NATURE, and do not reproduce with
organisms outside this classification. See
your notes for an elaboration on the various types of evidence for evolution and
proposed mechanisms of evolution.
Darwin's main ideas can be summarized in six basic points.
The first five are observations and the sixth point is his conclusion
based on these observations.
A group of organisms tend to reproduce more offspring than the environment can
Most populations tend to remain fairly constant in size because of various
population regulation mechanisms at work, e.g., density-dependent factors and
density-independent factors regulating population size.
The population comes into an equilibrium with its present environment.
(See your notes.)
Competition takes place because so many individuals are introduced into an
environment with limited resources. There
is a "struggle for existence." Such
a competitive struggle for existence usually includes being better adapted for
obtaining the available resources in comparison to other individuals.
Especially note that physical combat is not a very important part of this
There exists variation among individuals within any species because genetic
changes occasionally occur that modify the DNA structure of chromosomes.
Variations caused by gene mutations are usually either harmful or useless. However, over the course of time, beneficial mutations may
occur. Individuals that inherit
beneficial mutations or beneficial gene recombinations are better adapted to
survive. This is where the phrase
"survival of the fittest" comes in or the process of natural
selection. Again note that such a
competitive struggle for existence usually includes being better adapted for
obtaining the available resources in comparison to other individuals and that
physical combat is not a very important part of this concept.
In a changing environment, those organisms with favorable genetic variations
survive. The surviving organisms
then reproduce and transmit their DNA to their offspring.
Over a long period of time ENTIRELY NEW SPECIES EVOLVE.
Organisms that have successful genetic variations not only live longer
but produce more offspring who also inherit the favorable adaptation.
that the Theory of Natural Selection states that:
organisms that are better adapted (genetically) to their environment will
survive in greater
numbers than those less well adapted, and
b) the genetic material, therefore, that controls those adaptations will become more numerous
in the population in the next generation.
c) The ability of the entire group to survive in then increased.
selection is the preservation of favorable, beneficial characteristics in the
population and the elimination of the unfavorable characteristics.
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