In this essay I will talk about the theory of evolution. The term evolution
means a gradual change over time. There are two types of evolution. The first
is geologic evolution, which is the very slow change of the earth over a long
period of time. The second is organic evolution, which is the slow process by
which species change over a long period of time. The fossil record is
basically the history of life based on fossils found. A fossil is the remains of
an organism that lived at an earlier time. When insects are found they usually
are surrounded by amber. Amber is a yellow, sticky substance that hardens
over a period of time. When an insect get stuck in the amber, it hardens and it
is preserved. Petrifaction is when the remains of an organism is turned to
stone. Some fossils are petrified replicas of the first one.
Sedimentation is when any organism that has turned into a fossil, becomes
sedimentary rock and becomes a part of a layer on the earth. The youngest
fossils would be found at the top layer, and the oldest fossils would be found
at the lowest layer. Imprints are impressions made on the ground by an
organism. The imprint may remain if the surface turns into rock. A mold is a
hollow rock that has the remains of an organism inside it. The cast comes
from hardened minerals, that forms a copy of the original organism.
Comparative anatomy is the study of structural similarities and differences
among living things. It offers evidence that species have evolutionary
relationships. Homologous structures are parts of organisms that have similar
structures and similar embryological development, but have different forms
and functions. For example, a human hand is used for grabbing things, while a
cats limb is used for walking.
Comparative cytology is when cell organs, like the cell membrane,
ribosomes, mitochondria, are similar in organisms of all types. Comparative
embryology is that comparison of different species while they are still in
embryological form. This can provide evidence of evolutionary relationships.
Some embryos of certain species show alike patterns in development. Some
of the similarities in the embryos support the idea that they have a common
evolutionary origin. Scientists have discovered that the closer the evolutionary
relationship of any species, the more alike their biochemical similarities are.
For example the similarity in structure of the hemoglobin molecules of
animals and the chlorophyll in molecules of plants. One of the first theories of
evolution was developed by Jean Baptiste de Lamarck in 1809. According to
his theory, evolution had two principles. The first principle was the law of use
and disuse. It said that the more a part is used on an organism, the stronger
and better it will become, and the less a part of an organism is used, it will
become weaker, and less developed. The second principle was the inheritance
of acquired characteristics. It said that the characteristics of an organism
developed through use and disuse could be passed on to its offspring. Charles
Darwin is the man who developed the theory of natural selection. The idea of
it was that organisms with favorable variations would be better able to
survive and to reproduce better then organisms with less favorable variations.
There are four points of his theory that I will go over. The first is
overpopulation, which is when more offspring are produced than can survive,
because of limitations of food and shelter. The second is competition, which
is when individuals of each generation compete for available food and for
opportunities to mate and reproduce. The third is variation, which is when
some individuals in a generation are better fitted to survive than others,
because of variations in characteristics.
The fourth is survival of the fittest, which is when individuals better
fitted to survive are more likely to live long enough to reproduce. A weakness
in Darwin’s theory was that it did not explain how variations arose. DeVries
found that mutations gave new traits and that permitted evolution to occur.