Introduction To Evolution


What is Evolution? Evolution is the process by which all living things
have developed from primitive organisms through changes occurring over billions
of years, a process that includes all animals and plants. Exactly how evolution
occurs is still a matter of debate, but there are many different theories and
that it occurs is a scientific fact. Biologists agree that all living things
come through a long history of changes shaped by physical and chemical processes
that are still taking place. It is possible that all organisms can be traced
back to the origin of Life from one celled organims.

The most direct proof of evolution is the science of Paleontology,
or the study of life in the past through fossil remains or impressions, usually
in rock. Changes occur in living organisms that serve to increase their
adaptability, for survival and reproduction, in changing environments. Evolution
apparently has no built-in direction purpose. A given kind of organism may
evolve only when it occurs in a variety of forms differing in hereditary traits,
that are passed from parent to offspring. By chance, some varieties prove to be
ill adapted to their current environment and thus disappear, whereas others
prove to be adaptive, and their numbers increase. The elimination of the unfit,
or the "survival of the fittest," is known as Natural Selection because it is
nature that discards or favors a particular being. Evolution takes place only
when natural selection operates on apopulation of organisms containing diverse
inheritable forms.

HISTORY

Pierre Louis Moreau de Maupertuis (1698-1759) was the first to
propose a general theory of evolution. He said that hereditary material,
consisting of particles, was transmitted from parents to offspring. His opinion
of the part played by natural selection had little influence on other
naturalists.
Until the mid-19th century, naturalists believed that each species
was created separately, either through a supreme being or through spontaneous
generation the concept that organisms arose fully developed from soil or water.
The work of the Swedish naturalist Carolus Linnaeus in advancing the classifying
of biological organisms focused attention on the close similarity between
certain species. Speculation began as to the existence of a sort of blood
relationship between these species. These questions coupled with the emerging
sciences of geology and paleontology gave rise to hypotheses that the life-forms
of the day evolved from earlier forms through a process of change. Extremely
important was the realization that different layers of rock represented
different time periods and that each layer had a distinctive set of fossils of
life-forms that had lived in the past.

Lamarckism

Jean Baptiste Lamarck was one of several theorists who proposed an
evolutionary theory based on the "use and disuse" of organs. Lamarck stated that
an individual acquires traits during its lifetime and that such traits are in
some way put into the hereditary material and passed to the next generation.
This was an attempt to explain how a species could change gradually over time.
According to Lamarck, giraffes, for example, have long necks because for many
generations individual giraffes stretched to reach the uppermost leaves of trees,
in each generation the giraffes added some length to their necks, and they
passed this on to their offspring. New organs arise from new needs and develop
in the extent that they are used, disuse of organs leads to their disappearance.
Later, the science of Genetics disproved Lamarck\'s theory, it was found that
acquired traits cannot be inherited.

Malthus

Thomas Robert Malthus, an English clergyman, through his work An
Essay on the Principle of Population, had a great influence in directing
naturalists toward a theory of natural selection. Malthus proposed that
environmental factors such as famine and disease limited population growth.

Darwin

After more than 20 years of observation and experiment, Charles
Darwin proposed his theory of evolution through natural selection to the
Linnaean Society of London in 1858. He presented his discovery along with
another English naturalist, Alfred Russel Wallace, who independently discovered
natural selection at about the same time. The following year Darwin published
his full theory, supported with enormous evidence, in On the Origin of Species.

Genetics

The contribution of genetics to the understanding of evolution has
been the explanation of the inheritance in individuals of the same species.
Gregor Mendel discovered the basic principles of inheritance in 1865, but his
work was unknown to Darwin. Mendel\'s work was "rediscovered" by other scientists
around 1900. From that time to 1925 the science of genetics developed rapidly,
and many of Darwin\'s ideas about the inheritance of variations were found to be
incorrect. Only since 1925 has natural selection again been recognized as
essential in