Source:
www.talkorigins/faqs/faq-intro-to-biology.html
If you want to read the entire article, visit the above site and read it.
I only included the portion of the article where micro-evolution and
macro-evolution are defined and explained. Several people in this
newsgroup claimed or at least implied that I "made up" or "created" the
terms. It
should now be obvious that the terms (micro/macro evoluiton) are used
by people other than myself. I should note that those two terms are used
on a regular basis in the ICR newsletters. Here it is:
"Evolution is the cornerstone of modern biology. It unites all the fields
of biology under one theoretical umbrella. It is not a difficult concept,
but very few people -- the majority of biologists included -- have a
satisfactory grasp of it. One common mistake is believing that species can
be arranged on an evolutionary ladder from bacteria through "lower"
animals, to "higher" animals and, finally, up to man. Mistakes permeate
popular science expositions of evolutionary biology. Mistakes even filter
into biology journals and texts. For example, Lodish, et. al., in their
cell biology text, proclaim, "It was Charles Darwin's great insight that
organisms are all related in a great chain of being..." In fact, the idea
of a great chain of being, which traces to Linnaeus, was overturned by
Darwin's idea of common descent.
Misunderstandings about evolution are damaging to the study of evolution
and biology as a whole. People who have a general interest in science are
likely to dismiss evolution as a soft science after absorbing the pop
science nonsense that abounds. The impression of it being a soft science
is reinforced when biologists in unrelated fields speculate publicly about
evolution.
This is a brief introduction to evolutionary biology. I attempt to explain
basics of the theory of evolution and correct many of the misconceptions.
What is Evolution?
Evolution is a change in the gene pool of a population over time. A gene
is a hereditary unit that can be passed on unaltered for many generations.
The gene pool is the set of all genes in a species or population.
The English moth, Biston betularia, is a frequently cited example of
observed evolution. [evolution: a change in the gene pool] In this moth
there are two color morphs, light and dark. H. B. D. Kettlewell found that
dark moths constituted less than 2% of the population prior to 1848. The
frequency of the dark morph increased in the years following. By 1898, the
95% of the moths in Manchester and other highly industrialized areas were
of the dark type. Their frequency was less in rural areas. The moth
population changed from mostly light colored moths to mostly dark colored
moths. The moths' color was primarily determined by a single gene. [gene:
a hereditary unit] So, the change in frequency of dark colored moths
represented a change in the gene pool. [gene pool: the set all of genes in
a population] This change was, by definition, evolution.
The increase in relative abundance of the dark type was due to natural
selection. The late eighteen hundreds was the time of England's industrial
revolution. Soot from factories darkened the birch trees the moths landed
on. Against a sooty background, birds could see the lighter colored moths
better and ate more of them. As a result, more dark moths survived until
reproductive age and left offspring. The greater number of offspring left
by dark moths is what caused their increase in frequency. This is an
example of natural selection.
Populations evolve. [evolution: a change in the gene pool] In order to
understand evolution, it is necessary to view populations as a collection
of individuals, each harboring a different set of traits. A single
organism is never typical of an entire population unless there is no
variation within that population. Individual organisms do not evolve, they
retain the same genes throughout their life. When a population is
evolving, the ratio of different genetic types is changing -- each
individual organism within a population does not change. For example, in
the previous example, the frequency of black moths increased; the moths
did not turn from light to gray to dark in concert. The process of
evolution can be summarized in three sentences: Genes mutate. [gene: a
hereditary unit] Individuals are selected. Populations evolve.
Evolution can be divided into microevolution and macroevolution. The kind
of evolution documented above is microevolution. Larger changes, such as
when a new species is formed, are called macroevolution. Some biologists
feel the mechanisms of macroevolution are different from those of
microevolutionary change. Others think the distinction between the two is
arbitrary -- macroevolution is cumulative microevolution.
The word evolution has a variety of meanings. The fact that all organisms
are linked via descent to a common ancestor is often called evolution. The
theory of how the first living organisms appeared is often called
evolution. This should be called abiogenesis. And frequently, people use
the word evolution when they really mean natural selection -- one of the
many mechanisms of evolution.
--
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