"Nothing in biology makes sense except in the light of evolution."
Theodosius Dobzhansky, "The American Biology Teacher" (1973).
Source of this essay:
The following essay is based on many documents
found on the Internet and in reference texts. Quotations are taken from a definition of evolution
issued in 1997 by the National Association of Biology Teachers. The full
statement is available online. 1That statement was revised by the NABT from an earlier, 1995 statement.
The 1997 version was subsequently endorsed by:
The Society for the Study of Evolution, 1998-JUN.
The American Association of Physical Anthropologists, in 1998-JUL.
Definitions:
Evolution is "an unpredictable and
natural process of temporal descent with genetic modification that is
affected by natural selection, chance, historical contingencies and changing
environments." Note that evolution is limited to plant and animal
species. Its starting point is at the first life form -- a single celled
animal.
Natural selection is the primary mechanism driving evolutionary change
in species of plants and animals.
It is caused by variations which exist within a species due to differences
in the genetic makeup of its individual members. This causes some
individuals to be more likely to thrive in a given environment, and to
produce offspring like themselves.
Punctuated equilibrium is the concept that evolution did not
happen at a slow steady rate, as Charles Darwin had assumed. Rather, new
species typically develop very quickly within a small, peripheral group
which is isolated from the main "tribe" and subjected to different
evnironmental stressors. Thus, the fossil record shows long periods of
relative stability of a given species.
These periods were broken by short periods of rapid change.
Common misunderstanding:
Evolution's present scope includes:
All of the plant and animal species that are currently alive,
All of the species which have become extinct, and
Predictions of what species may develop in the future.
Studies of the origin of the first life form, of the origin of the
earth, and the origin of the universe itself do not form part of the
theory of evolution. Such studies are pursued within different
scientific disciplines.
Some proponents of other belief systems often use the term "evolution"
to refer to change in:
Plant and animal species,
The earth itself,
Individual stars,
Individual galaxies,
etc.
Strictly speaking, evolution belongs only in biology.
Natural selection does not necessarily imply that new species
evolve because some animals are more efficient killers. This is the "nature
red in tooth and claw" concept. Natural selection simply implies
survival of the fittest. Those those animals which are better able to
reach maturity and propagate are favored. This may be as a result of
animals having greater speed, better agility, greater intelligence,
better cooperative skills, etc.
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General considerations:
"The diversity of life on earth is the outcome
of evolution..." Extensive evidence of this is seen in the fossil
record.
Evolution is driven by natural selection of which numerous examples exist,
"both extant and extinct."
The earth is about 4.5 billion years old. Humans have been on earth for a
miniscule percentage of that interval.
Evolution has no specific goal.
Radiometric and other analyses have been developed which permit the
accurate dating of rock samples.
Evolution and the scientific method:
"...the
processes of science are characterized by asking questions,
proposing hypotheses, and designing empirical models and
conceptual frameworks for research about natural events."
The term "theory" in science does not refer to a wild
guess, as it does in normal usage. A scientific theory is a widely accepted
belief, solidly based on evidence.
The scientific method is self-correcting. Scientists' understanding of
evolution and its processes change as new evidence become available.
Evolution plays a central, unifying role in our understanding of nature.
Modern biologists accept that evolution happened; the fact of evolution is
not widely debated. However, scientists do debate the "patterns, mechanisms and pace"
of the evolutionary processes.
A study of evolution leads to new concepts for useful research.
Evolution and religion:
The scientific method "neither refutes nor supports the existence
of a deity or deities."
Creation science beliefs (a.k.a. scientific creationism, intelligent
design, young earth theory, etc.) are non-scientific systems because they
cannot be falsified. That is, their supporters cannot accept the possibility
that their fundamental beliefs are false.
Supporters of creation science tend to start with a fixed belief system
derived from a religious text, and attempt to support that belief by
searching for compatible evidence.
Non-scientific beliefs should
not be taught in the science classroom.
Conflicts between evolution and creation science:
Creation scientists often charge that evolution is impossible because it violates the second law
of thermodynamics, which implies that ordered systems become
disordered. That law only applies to isolated systems. Order can evolve from
disorder if energy comes from an outside source, like the sun.
The modern concept of punctuated equilibrium does not negate evolution; it
enlarges it.
Teaching about origins:
Evolution should be a
recurrent theme " throughout biology textbooks and courses."
There need not be any conflict between a teacher's or a student's
religious beliefs, and the teaching of scientists' conclusions about
evolution.
Comparing religious beliefs with scientific theories does not play a role
in the teaching of science.