FREE ESSAY ON INTERNET HISTORY

INTERNET HISTORY

volution 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. 
Common Misconceptions about Evolution
Evolution can occur without morphological change; and morphological change can occur
without evolution. Humans are larger now than in the recent past, a result of better diet
and medicine. Phenotypic changes, like this, induced solely by changes in environment do
not count as evolution because they are not heritable; in other words the change is not
passed on to the organism's offspring. Phenotype is the morphological, physiological,
biochemical, behavioral and other properties exhibited by a living organism. An
organism's phenotype is determined by its genes and its environment. Most changes due to
environment are fairly subtle, for example size differences. Large scale phenotypic
changes are obviously due to genetic changes, and therefore are evolution. 
Evolution is not progress. Populations simply adapt to their current surroundings. They
do not necessarily become better in any absolute sense over time. A trait or strategy
that is successful at one time may be unsuccessful at another. Paquin and Adams
demonstrated this experimentally. They founded a yeast culture and maintained it for many
generations. Occasionally, a mutation would arise that allowed its bearer to reproduce
better than its contemporaries. These mutant strains would crowd out the formerly
dominant strains. Samples of the most successful strains from the culture were taken at a
variety of times. In later competition experiments, each strain would outcompete the
immediately previously dominant type in a culture. However, some earlier isolates could
outcompete strains that arose late in the experiment. Competitive ability of a strain was
always better than its previous type, but competitiveness in a general sense was not
increasing. Any organism's success depends on the behavior of its contemporaries. For
most traits or behaviors there is likely no optimal design or strategy, only contingent
ones. Evolution can be like a game of paper/scissors/rock. 
Organisms are not passive targets of their environment. Each species modifies its own
environment. At the least, organisms remove nutrients from and add waste to their
surroundings. Often, waste products benefit other species. Animal dung is fertilizer for
plants. Conversely, the oxygen we breathe is a waste product of plants. Species do not
simply change to fit their environment; they modify their environment to suit them as
well. Beavers build a dam to create a pond suitable to sustain them and raise young.
Alternately, when the environment changes, species can migrate to suitable climes or seek
out microenvironments to which they are adapted.