Biological evolution is the change in the physical characteristics of any species through several generations. Evolution depends on natural selection, which is a process of nature selecting species that are better and fit to survive compared to other species.

Natural selection acts on the phenotype of a species, and the phenotype mostly depends on the genetic composition of a species. Changes in the genetic composition lead to mutation, and these mutations give rise to phenotypic variation. There have been many theories stating evolution and what it is. But the accepted theory of evolution is the one given by Charles Darwin and Alfred Russel Wallace.

History 

• In 1809 Jean-Baptiste Lamarck came up with his ‘Transmutation’ theory about spontaneous generation. In his theory, he mentioned how the unused organs or body parts are removed from generations of species and the used parts are enhanced. 
• Darwin came up with the idea of natural selection from his book, which was very much similar to that of what Alfred Russel Wallace had written in the year 1858. Though both the scientists had written the same thing, Darwin’s writing was more widely accepted.
• But due to a lack of knowledge in genetics, Darwin’s theory faced a lot of contradictions which was later reconciled in the 1930s by Ronald Fisher, Sewall Wright, and JBS Haldane.
• Therefore, in the 1930s, the modern theory of evolution came into play which stated the link between natural selection and genetics.

Biological Evolution Meaning

Evolution means changes that occur in any species over time which can divide a single species into two different species. The process of development of humans from apes is nothing but a classic example of evolution. It tells us how the accumulation of small changes transformed one type of species into another, like in our case. Apes were transformed into humans with the accumulation of small changes.

Evolution, which is a time-taking process, causes changes in the traits of an organism that can be inherited. Inherited traits depend on genes within the genome which are known as genotype.

The characteristics which appear in an organism, like the structure, colour, size, etc., are known as the phenotype. The phenotype is nothing but the outcome of the interaction between the genotype and the environment. The traits that are passed on from one generation to another are through the genetic material DNA, deoxyribonucleic Acid.

Causes of Variations

The concept of evolution came from variations. If there is no variation, then there is no evolution. The variation that occurs at the genetic level is generally the one that causes evolution. Apart from that, different reasons can lead to variations, like-

• Mutation – It is generally the change in DNA sequence in the genome. It can change the gene product, leading to the development of different characteristics. Mutation can be caused by different phenomena like genetic recombination, where genes can be duplicated, deleted, etc. The presence of a copy of the existing genes generally leads to major changes and helps in evolution.
• Recombination – In sexual reproduction, genetic material from both the parent’s mix to form a new offspring with few changes. The process is known as homologous recombination, where the DNA is exchanged between 2 similar chromosomes and is then inherited by the offspring, causing slight variation. Thus, sexual reproduction also plays a major role in evolution.
• Gene flow – It means the transfer of genes between species of the same population or different populations. It can be caused by the movement of species from one place to another or by the formation of hybrids. Therefore, as genetic material transfers, even gene flow is a great cause of evolution.

Mechanism of Evolutionary Processes

Many mechanisms can lead to evolution like-

• Natural selection- Here, characters that are more fit to survive are naturally chosen, and similar characters are inherited by the next generations. It generally acts on the phenotype of an organism. The variation in phenotype is caused due to changes in the genotype.
• Genetic drift- It is the random changes in the allelic frequencies which can cause variation and lead to evolution.

Conclusion

Evolution is defined as a time taking process where small genetic changes accumulate over time to cause a phenotypic change leading to the formation of a new species. Evolution occurs mostly on the basis of Natural Selection. It is a process of nature to select species that are better and fit to survive compared to other species.

Natural selection acts on the phenotype of a species, and the phenotype mostly depends on the genetic composition of a species. Changes in the genetic composition lead to mutation, and these mutations give rise to phenotypic variation. Charles Darwin’s Theory of natural selection is the most widely accepted theory for evolution. Due to his findings in the field of evolution, he is known as the Father of Evolution.