The theory of evolution: What
believe it is, and is not.
Quotations demonstrating very different views of evolution:
"Nothing in biology makes sense except in the light of evolution."
Theodosius Dobzhansky, "The American Biology Teacher" (1973).
"Darwinism plays an indispensable ideological role in the war against fundamentalism. For that reason, the scientific organizations are devoted to protecting Darwinism rather then testing it, and the rules of scientific investigation have been shaped to help them succeed."¬ Philip E. Johnson, California University¬
Source of this essay:
The following essay is based on many documents
found on the Internet and in reference texts. Definitions are taken from a report
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.
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 biological organisms (i.e., all life, including bacteria, plant, animal
species, etc.) Its starting point is at the first life form -- a single celled
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 similar to 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
environmental 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 beliefs that are misunderstood:
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. Research into the origin of the first form of life is called abiogenesis, and is not part of evolution. The origin of the universe and and its changes over time are called cosmology.
Some proponents of other belief systems often loosely use the term "evolution"
to refer to change in:
Plant and animal species,
The earth itself,
Strictly speaking, Evolution really only deals with species of living -- or once living -- biological species.
Natural selection does not necessarily imply that new species
evolve because some animals are more efficient killers. That 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, better defenses against attacks, etc. In the case of humans, greater intelligence,
better organizational skills and cooperative methods are even more important.
The term "theory" has multiple meanings. In popular use, it is often defined as a hunch or guess based on inadequate and incomplete data. Detectives pursue theories on crime TV shows hoping that they might lead somewhere. The word has a very different meaning in science. Rather, it is an: ..."extensive explanation developed from well-documented, reproducible sets of experimentally-derived data from repeated observations of natural processes." To avoid confusion, authors need to differentiate between these two definitions. Unfortunately, some authors prefer to cause confusion, by making statements like: "Evolution is just a theory."
Humans are not the descendents of apes: Charles Darwin, the person who founded the theory of evolution in the mid 19th century, believed that humans are not the descendents of apes. Rather, apes and humans had a common ancestor. Further, he believed that any two species -- e.g. humans and apes, have common ancestor. So do dogs and birds, even oak trees and sponges.
The theory of evolution does not violate the second law
of thermodynamics. That law implies that ordered systems always become
more disordered, not more ordered. That law only applies to isolated systems. Order can and does evolve from
disorder if energy enters the system from an outside source, like the sun. So, within the solar system, evolution towards more complex forms of life can occur even as the sun runs down.
Darwinism is not the theory of evolution: "Darwinism" is a term used by many conservative religious persons to refer to the theory of evolution. The implication is that there have been no developments in the field since Darwin published his findings during the 19th century. In reality, the discovery of genes and DNA as well as over a century of work by biologists, palentologists, and others have extensively modified his original teachings.
General considerations about the theory of evolution that are generally accepted by most scientists:
"The diversity of life on earth is the outcome
of evolution..." Extensive evidence of this is seen in the fossil
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 of species has no specific goal.
Evolution is largely guided by environmental factors
and is not part of a grand plan to produce some ultimate species, like humans.
If it were possible to go back in time and restore all life on Earth to what was present at that time, intelligent life may or may not have subsequently developed; species similar to humans may or may not have come into existence.
Radiometric and other analyses permit the
accurate dating of rock samples.
Evolution and the scientific method:
processes of science are characterized by asking questions,
proposing hypotheses, and designing empirical models and
conceptual frameworks for research about natural events."
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.
Essentially every modern biologist accepts 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 has lead -- and is expected to continue leading -- to new concepts for useful research.
Evolution and religion:
The scientific method "neither refutes nor supports the existence
of a deity or deities."
Since the existence of gods, goddesses and pantheons of deities can neither be proven nor disproved, and cannot be detected or measured, the scientific method has nothing to say on their existence.
Creation science beliefs (including 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.
However, because they are so important to many religious faiths, it some educators believe that they should be taught in comparative religion classes.
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
Comparing religious beliefs with scientific theories does not play a role
in the teaching of science.