Organismic evolution concerns changes in species and groups of species. However, an even better definition would posit that evolution occurs because of variation in the frequency of heritable traits that appear over the passing of different generation in a population. Evolution is studied at two different levels: microevolution and macroevolution. Microevolution is concerned with changes in populations of organisms from generation to generation and how new species come about. Macroevolution studies the patterns of changes in species over prodigious amounts of time; these patterns are used to determine evolutionary relationships among species, which are called phylogeny. Both levels are concerned with Charles Darwin’s theory that natural selection, which is also known as “survival of the fittest,” is the driving force of evolution. Darwin ’s theory has also been refined and made more comprehensive and is termed neo-Darwinism or the synthetic theory of evolution.
Evidence for Evolution
Five different scientific disciplines have been able to provide evidence for evolution through their research: paleontology, biogeography, embryology, comparative anatomy, and molecular biology.
Paleontology
The study of paleontology has provided us with a fossil record of the primordial existence of species that are now extinct. Furthermore, because deposits of sediment layer are essentially pictures of geologic time periods, fossils of the similar organisms have been removed from the successive layer and compared, illustrating to scientists a clear evolutionary relationship. For instance, a fossil of an oyster shell extracted from successive layers of sediment deposits illustrate a gradual alteration in the size of the shell followed by rapid alteration in the size of shells. These rapid alterations in size change mark the production of a new species of oyster.
Biogeography
Scientists in the field of biogeography, who employs the study of geography to describe the distribution of organisms, have pointed out that there are species without relation in different geographical areas of the globe that look strikingly similar when found in analogous environments. For example, the wallaby, a marsupial mammal that is native to Australia , and the rabbit, a placental mammal that is not native to Australia , are very similar in appearance and behavior.
Embryology
By studying the development of embryos of different organisms, scientists have been able to establish many stages that are the same among related species. Embryology has helped connect many species and establish evolutionary relationships. An example of the similarities in embryological development can be observed among species such fish, chicken, and pig, which all have gill slits and tails during their times as embryos.
Comparative Anatomy
Scientists use comparative anatomy to analyze different anatomical structures between species to look for evolutionary relationships. Two different types of anatomical structures exists that help identify evolutionary relationships among species; they are called homologous structures and analogues structures. Homologous structures are a part of an organism’s body that resembles a body part of a different organism of another species; the resemblance exists because of a common ancestor shared by the organisms of different species. The forelimbs of bats, humans, and whales are a paradigmatic example of homologous structures because their forelimbs are evolved from a common ancestral mammal. Analogous structures are parts of organisms’ bodies that are similar to one another across different species because these different species independently evolved adaptations due to a similar environment or selection pressure instead of from a common ancestor. The fins and bodies shapes of porpoises and sharks are a great example of analogous structures.
Molecular Biology
Molecular biologists study the nucleotides and amino acid sequences in the genomes of various species and compare them to develop evolutionary relationships. Species that are more closely related have higher percentages of similar genetic sequences than those of unrelated species. Humans and chimpanzees are 98% identical based on their genetic information.
The evidence for evolution is overwhelming. It is a very intriguing part of biology and plays an integral part in the world we live in today.
Sources
- Pack, Phillip E. CliffsAP Biology. Hoboken: Wiley Publishing, Inc., 2007. Print.
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