Evolution
The process by which all living things have developed from primitive life
forms
through changes occurring over billions of years is evolution. All
living things
arose through a long history of changes formed 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 inanimate matter.
Paleontology is the
most direct proof of evolution because it studies life of
the past.
Approximately 2 million different species of organisms are now
living, but at
least 99.9 percent of the species that have ever lived are now
in extinction and
about 2 billion species have evolved during the past 600
billion years (Burkhardt
19). One of the firsts to propose a general
theory evolution was Pierre Louis de
Maupertuis. His theory was that
hereditary material, consisting of particles,
was transmitted from parents to
their offspring. Until the mid 19th century
naturalists believed that each
species was created separately by a supreme being
or through spontaneous
generation, the concept that organisms arose from the
soil or water. Carolus
Linnaeus, a Swedish naturalist who classified biological
organisms, focused
his attention on the similarities of certain species. There
was speculation
of a blood relationship between those species. From these
questions and the
rise of the new sciences of geology and paleontology arose the
hypothesis
that the life forms of the day evolved from earlier forms through a
process
of change. Also the extremely important discovery that different layers
of
rock showed different time periods and that each layer had a distinctive
set
of fossils of life forms that had lived in the past. During the Devonian
Period
(390-340 million years ago) the Earth was largely barren of animal
life.
However, the seas were crowded with many invertebrates,
cartilaginous and bony
fish. A prominent bony fish, the Crossopterygii,
possessed the ability to rise
to the surface and gulp air. This fish was one
of the first amphibians. What led
the Crossopterygii to venture on to land is
still under speculation by
scientists. The Crossopterygians were crudley
adapted for land existance but
bacause they had no competitors they
survived.