Evidence of Evolution
Let's have a look at the type of
evidence that supports Darwin's theory of evolution and the modern
synthesis, which combines natural selection with the concept of
species and population genetics. The latter is the modern application
of the patterns of inheritance as first described by Gregor Mendel
(1822-1884), a contemporary of Charles Darwin (1809 -1882).
of evolution comes from categorizing similarities among organisms
living on distant locations, e.g., continents. Biogeography was
central to Darwin's logic when he summarized his findings from five
years of collecting evidence around the world as a passenger on
the HMS Beagle. He realized that animal and plant species, though
diverse, were more similar to each other on the same continent.
Australian species were more similar to each other than they were
to South American species. But such geographic diversity also played
out on local island groups such as those of the Archipelago Galapagos
in the South Pacific. The famous Darwin finches were his prime exhibit
in formulating the theory of evolution. The idea is that species
change over time in different direction if they live isolated from
each other over long periods of time. Time periods in evolution
are truly long and are measured in geological time, e.g. MYA or
million years ago.
Fossil records together with the
theory on plate tectonics and continental drift support the idea
of speciation as a result of long lasting geographic isolation.
Speciation is the process of evolving two separate species from
a founder species after an event caused separation of the founder
population into two isolated population where individuals from one
population cease to reproduce with individuals from the other population.
Evidence of diversity and similarity
comes from comparative anatomy and comparative embryology. Often,
we find similar anatomical features in animals and plants that are
used for different functions. Examples are the human arm used for
grabbing, whose skeletal anatomy looks similar to that of the forelimb
of a cat used for walking, but also looks similar to the skeletal
anatomy of the flipper of a whale used for swimming and the wing
of a bat, used for flying. The bone structures in all four limbs
are strikingly similar in their anatomical plan, suggesting that
the four different animals are all descendants of a common ancestral
animal form. Each modern animal has evolved independently of all
others and has adapted a limb structure that fits the different
usage. They have, however, not changed completely and are considered
homologous structures. The idea of homology points towards a structural
similarity of body parts that are used for different functions.
In some instances, organisms that are clearly not related have evolved
similar structures for the same function. This structural similarity
for the sake of the same function is the result of convergent evolution.
Such structures are called analogous, indicating that their similarity,
unlike the structural similarities of homologous structures, is
not the result of descent with modifications.
Some of the most convincing evidence
comes from modern molecular biology demonstrating that similarities
at the molecular level - protein structures and gene sequences -
can be used to determine evolutionary relationship. Molecular evidence
has spectacularly supported the theory of evolution The power of
molecular analysis is straight forward; the modifications mentioned
by Darwin are really the result of random mutations in our genes.
Genes contain the instructions to make proteins. Proteins are the
true causes of physical traits. It is these traits that are edited
by natural selection, i.e., how well an individual organism can
live in changing environments and has the opportunity to have as
much offspring as possible. It is the number of fertile offspring
that is the true measure of Darwinian fitness. It is not, as many
people believe, the survival of the fittest, often meant to mean
the strongest individual. The meaning of strength is relative and
is often shaped by chance events. As a result, descent with modification
is neither directed nor is it able to create the perfect species.
Perfection often means reduced ability to adapt, to make use of
modifications when the environment changes drastically. Drastic
changes are thought to be global climate changes such as warming
and cooling. Most organisms are very sensitive to the average temperature,
or their food, i.e., the organisms they feed on may be very sensitive
to changes in temperature and disappear, leaving even the strongest
of animals in limbo, without food, and thus may risk extinction
if it cannot change its way of life.
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Copyright © 1999-2011
Lukas K. Buehler