Introduction:
Darwin’s theory of origin of new species was supported by a number of scientists like Wallance, Haeckel, Weismann, Mendel etc. These supporters are known as the Neo-Darwinians, and the concept is called Neo-Darwinism. The modern synthetic theory explains the genetic basis of the adaptation of a population to new environmental conditions. It includes the following concepts.
- Mutation
- Genetic recombination
- Natural Selection
- Isolation
- Genetic drift
Mutation:
It can be characterized as rapid, random, heritable variations in organisms. New species are formed due to discontinuous variation causes due to mutation. There are two types of mutation
Chromosomal mutation
The sudden and random change in the structure or arrangement of chromosome is called chromosomal mutation.
Gene mutation
The change in the structure of gene or DNA due to addition, deletion, inversion, or substitution of nucleotides is known as gene mutation.
These mutation causes variations in the population which plays a significant role in bringing evolution in organisms. Mutation is now considered as the ultimate source of organic evolution. Due to mutations some old genes can be replaced by new genes in a population to develop changes and thus, mutation play an important part in the process of organic evolution.
Genetic recombination:
It is the process of recombination or reshuffling of genes between different organisms. As a result, the new recombinations with new genotypes are produced. It occurs in sexual reproducing populations. Gene recombination occurs during;
- Crossing over during prophase I of meiosis
- During gametic development, there is a free assortment of genes.
- A random combination of gametes occurs during fertilization.
Genetic recombination is the major source of observable genetic variation in the population which is significant event in evolution and the formation of new species.
Natural Selection:
This is the principal element of Darwin’s theory. According to him, in nature, organisms face over lasting competition or struggle among them. In such competition, the strongest win and survive, while the weakest are removed. The individuals with favorable variations have a better chance of survival in the competition but another die. Thus, nature is the supper power that select the best fitted individuals and reject those that are poorly developed which is known as natural selection.
Organisms became more adaptable to their surroundings as a result of constant variation. The variation gets inherited to its progeny. These alterations or adaptations were also maintained or accumulated by progeny. After successive generations, the organisms became different from its parent. As a result, a new species emerges, which differs significantly from its ancestor.
Isolation:
Isolation is the process of separation of organisms from their original population. Its results in the prevention of mating amongst interbreeding groups. Isolation occurs due to physical (e.g., geographical, ecological) and biotic (e.g., Physiological, behavioral, mechanical, genetic) barriers.
Types of isolation: There are two main types of isolation.
Geographical isolation
It is the most common types of isolation and occurs when an original population is divided into two or more groups by geographical barriers such as mutation, river, glacier, ocean, forests, deserts, etc. that prevent interbreeding between that groups of population.
Reproductive isolation
It is the prevention of interbreeding between the population of two different species. When potential mates are present in the same area but are either unbale to mate due to morphological or psychological or physiological differences that maintains the characters of the species but can lead to the origin of new species.
Genetic drift:
The random changes in allele number and allele frequencies in a gene of population occurring by chance alone rather than natural selection are called genetic drift. It causes variation in gene frequencies within population. The population of a specific species may decrease significantly as a result of an epidemic. Some individuals migrate to anew habitat or to some remote island and variability in reduced rapidly. This genotype tends to differ and such population starts differing from the original population to become distinct stocks or different race. This process is called genetic drift. Genetic drift may be an important mechanism in evolutionary change in small or isolated population. It is thought to have been a significant factor in the origin of new species.