Genetic Evolution of Species | Cell Biology

In this article we will discuss about the Introduction and Present Status of Genetic Evolution of Species.

Introduction to Genetic Evolution of Species:

The concept of ‘organic evolution’ envisages that all the living forms of today developed from a common ancestor. That is, the various life forms are related by descent, which accounts for the similarities among them. The idea of organic evo­lution was not widely accepted until 1859 when Darwin published his classic work ‘The Origin of Species’.

This work contained a large body of evidence in favour of the idea that evolution continuous and it provided an attractive hypothesis to explain the mode of evolution.

Subsequently, various concepts regarding the mechanism of evolution were developed Haldane, Fischer, Wright and several others, Information’s from diverse areas of study, such as, geology, palaeontology, taxonomy, population genetics, biochemistry, molecular genetics and others have been collated and resynthesized to understand evolution.

Present Status of Genetic Evolution of Species:

The modality of evolution of species in the plant kingdom involves a combination of pro­cesses and phenomena in nature. The processes cover all the changes inherent in the concepts of Drawin, de Vries, and lately by Stebbins.

The basic materials bringing about changes in the individual of a population, are the genes and their alterations. In fact, the random gene changes provide with basic raw materials in the evolutionary process.

Such changes may be major or minor, involving alterations in structure and numbers of genes as well as of chromosomes and chromosome segments. In short, genie and chromosomal alterations occurring at random in the individuals of a population, provide the basic materials for the evolution.

The next step in the evolutionary process at the population level, is the recombination of genes between different individuals. The random hybridization between different individuals containing different genetic changes leads to the origin of new individuals with newer gene combinations. At this step, the population may represent a heterogeneous mass of individuals containing different gene combinations.

The next step in evolution is the operation of natural selection in the struggle for existence among the heterogeneous recombination’s, for opti­mum utilization of the resources in their specific environments. Ultimately through natural selec­tion, certain individuals with altered gene com­plements occupy the environmental niche with the gradual exclusion of others.

Through cross bree­ding amongst themselves, such a population ulti­mately becomes stable with specific altered gene combinations and becomes a stable genotype.

The stable population characterized by a particular gene combination, stands apart from the parental species to which the population initially belonged. Such a stabilized population, characterizing a genotype differing in phenotype from its predecessors, is often considered as attaining an incipient species level.

Such an incipient species can even undergo intercrossing with individuals of the parental population and may lose identity.

Allopatric Speciation:

As such, the attain­ment of a species status from the level of incipi­ent species, would require a compatibility barri­er between the new and the old populations. Without this barrier, despite phenotypic differen­ces, the identity of the new population cannot be maintained.

There is every possibility of its mer­ger with parental species through breeding in absence of barrier leading to the origin of a series of graded phenotypes. The barrier to compati­bility, essential for attaining species status, can be achieved through different means.

The method without involving any genie changes leading to compatibility barrier is migration. The migration of the new population to new environment, far removed from the original, leads to geographical isolation. Such geographical isolation enables a population to develop its own phenotypic cha­racteristic adapted to the changed environment, far removed from the original.

Such species are also termed allopatric species.

Sympatric speciation:

The common method, other than the migration and consequent geo­graphical isolation, is the genie changes or muta­tions leading to a barrier to fertilization.

Such barrier to fertilization between species-occupying the same geographical area, otherwise termed as sympatric species, can be achieved through sea­sonal isolation, i.e., blooming at different seasons caused by genie changes in the individual.

Not necessarily seasonal, but the barrier may be pre­sent even between two species maintaining their individuality, occupying the same habitat and blooming in the same season. The compatible barrier between the two species, original and derived, can also be due to incompatibility of germinal line, the pollens and ovule.

Such genie sterility may be manifested either in the absence of fertilization or barrier to post-fertilization embry­onic development. Such sterility barrier at the genie level is the principal factor in stabilization and as such evolution of species.