What is "transition" and how does it effect evolution?
According to most scientific data, organisms evolve by the process of transition. Transition can be defined as a mechanism of evolution that is similar to other mechanisms, such as mutations.
In some cases, transitions are driven by:
Mutation, Genetic Drift, Gene Flow, Natural Selection, or any process that changes the allele frequency in a given population. However, most commonly, transitions is discussed on a molecular level involving DNA. Another definition for transition is "change of a pyrimidine nucleotide, C or T, into an other pyrimidine nucleotide, or change of a purine nuceotide, A or G, into an other purine nucleotide" (EMBL Outstation, Accessed 1/14/02).
Darwin proposed the first theory of transition when he journeyed to the Galapagos Islands. This theory was referred to as adaptation, but adaptation is just a form of transition. Darwin focused on eleven different species of finches that have adapted from one island to the next. These birds were separated by a geographical barrier and eventually became reproductively isolated into many different species (Campbell 418).
Some of the more recent evidence for transition comes from fossil records of organisms dating back to the oldest fossil found. Darwin proposed that all life on earth evolved through one common ancestor. Evidence from fossils may be the answer to this question. One fossil that was used as evidence for this theory is the fossil "Lucy." Lucy is believed to be the direct link between humans and chimpanzees. Lucy is a fossil of the genus Australopithecine, which has five different divisions. It is believed that she walked upright, in a more similar style to humans than apes. This is rationalized from the size of her femurs and other bone structures.
One attribute of organisms that allows us to link one species to another is molecular confirmation. Michael Benton, Ph.D. wrote a book on the subject of transitions seen through fossil records, in which he addresses this point. Through RNA and DNA scientists can find differences and similarities between genetic material of different species in different time frames. The similarities aid in the linkage from one species to the next. The major differences can be accounted for by time gaps, where a period of over 1 million years has lapsed without a fossil.
There are multiple pathways for molecular changes in DNA that result in transition, such as point mutations, crossing over , and chromosome inversions.
Does the discussion on transition sound a little far-fetched to you? If so, there are hundreds of books and papers written by prominent researchers that provide their discoveries first hand, and some of their work is rather interesting!! Check it out!
So, here's a question for you:
Are Transitions changes in a) appearance or b) molecular configuration?
Some evidence for molecular transitions is:
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b) fossils
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Created By: Chelsea K. Lattas