Evolution in a broad sense means ‘change’. Evolution is a sequence of events that occurs in a population over successive generation. These events happen in the genetic level and thus carried forward to the future generations. Evolution results in speciation i.e. creation of new species from existing species over time. The changes may include induction of new characteristics, restrain from existing character etc. Biological evolution refers to population and not to any individual. Evolution is not a fast process. Time matters…All the biodiversities in our earth is due to evolution. Evolution has left us with lot of evidences through which the history of different species is obtained. Fossils are very important in the study of evolution as they contain the earliest of life itself. The oldest known fossils are approximately 3.5 billion years old, but some scientists have discovered chemical evidence suggesting that life may have begun even earlier, nearly 4 billion years ago. A comparative study of fossils and present day plants/animals helps paleontologists to infer the lineages of those species. The development in the molecular genetics (mainly the DNA sequencing) is another main thing that aids in finding the lineages of a species. Geographical distribution of a species can also be considered. There are two basic mechanisms that produce evolutionary change: 1) Natural selection (which includes ecological, sexual, and kin selection) 2) Genetic drift; Both these two mechanisms act on the genetic variation created by mutation, genetic recombination and gene flow. In these modern times, the understanding of evolution is based on the Darwin's theory of evolution. Darwin is the first of the evolutionary biologists, the originator of the concept of natural selection. Charles Darwin was born on February 12, 1809, in Shrewsbury, England. The Darwins’s theory of evolution is on the natural selection process and is described in detail in his book of ‘The Origin of Species’, published in 1859. It is important to note that all the species are related to each other. This includes both living and extinct beings. Each pair of these species shares a common ancestor at some point of time in the evolution history, be it a chimpanzee and man or bacteria and man. Even though bacteria are single-celled, careful DNA analysis proves that humans still have more than 200 genes in common with bacteria!! Key Terms: Fossil - The remains (or an impression) of a plant or animal that existed in a past geological age and that has been excavated from the soil. DNA - Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the biological development of a cellular form of life or a virus. All known cellular life and some viruses have DNAs. Genes – It is a part of DNA which is responsible for the construction of any organism. Genes contain the traits of an organism. These are passed from parents to offspring. Genetic variations occur when molecular mechanisms alter the genes generation-to-generation. This is the key of evolution. Species - Taxonomic group whose members can interbreed. |
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