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Change in the genetic composition of a population over successive generations is termed Evolution. It is also defined as progressive change.
What is Evolution?
Interaction between available genetic variants and the environment is involved in the evolutionary changes. The vital key players for evolution include genetic variation, natural selection, and genetic drift.
The word evolution is derived from the Latin word “evolution” means “unfolding or unrolling”.
It is the essential factor for evolution. The variation must be inheritable from parents to their offspring to contribute to evolutionary change. The genes of the organism encode the transmissible traits. The chief sources of variation include mutation and recombination.
Mutation can be defined as the change in the genomic DNA that can occur due to random replication errors or by some environmental interactions.
Gene flow is the process that introduces new mutations into a population by individuals migrating from a differentiation population. The example of gene flow is different traits of eye color such as brown, green, blue, hazel, etc. the blue eye color in humans is a result of the specific mutation in the HERC2 genes.
The mutation reduces the melanin production that causes blue eye color. The studies also reveal that the mutation first occurs in a single European ancestor around 6,000 to 10,000 years ago, which later spread in the modern population.
The consequence of sexual reproduction is usually called recombination. In fertilization, the fusion of parental gametes may bring mutations acquired in different lineages.
Later, by independent assortment and by crossing over, the mutations recombine and inherit in the following generation. The meiotic events result in the production of new allelic combinations and increase genetic variation, thus sexual reproduction escalates evolution.
The theory of evolution by natural selection was first described by Charles Darwin in his book “The origin of species” in 1859. The theory describes that individuals with advantageous traits are more likely to reproduce with more success. These traits are called adaptive that pass into the next generation.
The adaptive traits are selected based on environmental conditions and mating choices. The selection of different sets of adaptive traits in species is called adaptive radiation that occurs in species living in different environmental conditions.
It is another mechanism that drives evolution. In a population, random changes in the frequency of traits are produced by genetic drift. Random changes have a greater effect in small populations thus genetic drift is more common in small populations. The example includes the Afrikaner population has a high incidence of Huntington’s disease due to the introduction of a gene by a small group of Dutch colonists.
Microevolution and Macroevolution
The levels of evolutionary changes include microevolution and macroevolution. The change in the gene frequencies in a single population for a relatively short period is termed microevolution whereas macroevolution is the change that occurs at or above the level of speciation. An example of microevolution is the population of finches in the Galapagos Islands that have mutations in the structure of the beak. The reproductive isolation in eukaryotes is the critical event for speciation.
Reproductive isolation is the inability of individuals from two different populations to produce viable progeny. It usually starts from the geographical isolation that leads to chromosomal changes and prevents chromosome pairing. The example is horses and donkeys that can produce a viable hybrid- mules but the mules can never produce progeny.
Study of Evolution
In biology, evolutionary biology is studied as a subfield that deals with the evolutionary process. A person who studies evolutionary biology is called an evolutionary biologist.
Charles Darwin is named as “father of evolutionary biology”. He proposed his theory of natural selection, which is presented jointly with Alfred Russel Wallace. Darwin later explicated his arguments in detail in his publication “On the Origin of Species” in 1859. He posited that natural selection causes evolutionary changes. Along with Darwin some other scientists also contributed to the field of evolutionary biology.
For example, Carl Linnaeus proposed the classification of organisms in 1735. Based on physical similarities and differences, he classified organisms into various hierarchical groups. The transmutation theory was proposed by Jean- Baptiste Lamarck, which explains the transmutation of species. The theory is regarded as the first fully formed theory of evolution.
In the present scenario, methods of mathematical and theoretical biology and molecular genetics are incorporated with evolutionary biology. The mathematical framework is used to reconcile Darwin’s theory of evolution and Mendel’s law of inheritance to come up with a unified theory of evolution.