Speciation And Evolution: Definition and Examples

Definition of Speciation and Evolution

Speciation can be defined as the process where some new distinct species are formed from already existing species. This occurs due to mechanisms that cause genetic differences as well as a lack of compatibility in reproduction. While, the process of evolution is defined as the change in the heritable characteristics of populations during successive generations influenced by factors like natural selection, mutation, gene flow, and genetic drift.

Combining concepts like speciation and evolution gives a clear perspective to the understanding of the differences in the forms of lives and their survival mechanisms in various ecosystems comprehensively identified as the ever-changing face of the Earth’s biodiversity.

Modes of Speciation

Speciation can occur through different modes based on how populations become reproductively isolated. These modes help explain how one species splits into two or more over time. Understanding the types of speciation provides insight into how biodiversity increases through evolution. The types of speciation are described below-

Mechanisms of Evolution

Evolution operates through various mechanisms such as natural selection, genetic drift, mutation, and gene flow. These processes bring about changes in the genetic makeup of populations over generations. Together, they drive the evolutionary journey of organisms. The mechanism is described below-

Natural Selection

Natural selection explains that certain favourable characteristics are likely to be passed by to the progeny. They include, the formation of antibiotic resistance in bacteria and the evolution of Darwin’s finches feeding habits.

Genetic Drift

Genetic drift refers to the probability of changes in allele frequencies within a gene pool, which is effective in small populations. Genetic drift is illustrated by events such as the bottleneck effect which refers to the reduction of population size and the founder effect which involves the establishment of a new population by a few individuals.

Gene Flow

Gene flow is the interchange or exchange of genes between populations and it leads to the introduction of certain factors that reduce the degree of dissimilarity between two populations.

Mutation

Genetic mutations can be regarded as the primary source of variation, beneficial or deleterious, in the known hereditary material sequence.

Factors Affecting Speciation and Evolution

Several factors influence how species evolve and new ones form such as geographical isolation, environmental changes, reproductive isolation, and genetic variations. These factors shape the direction of evolution. They are essential in studying the diversity and adaptation of life on Earth. The factors are described below:

Geographical Isolation

Geographical isolation, for example by mountains, rivers and seas, isolates populations and does not allow them to interbreed. This leads to the formation of a new species.

Case Study: The isolation of finch populations by being on different islands yet all parts of the Galapagos led to Darwin’s Finches owing to their different adapted beaks to feed from separate trees.

Reproductive Isolation

Reproductive isolation ensures that different species do not mate with one another. Some of the prezygotic barriers include temporal, which refers to species that only mate at different seasons. While behavioural, mechanical and gametic refers to species whose reproductive behaviours, structural attributes and sperm respectively are incompatible. Postzygotic barriers consist of reduced hybrid viability; offspring die in the process of their development, or hybrid sterility, and offspring cannot reproduce.

Ecological Factors

One of the speciation mechanisms involves differences in ecological roles that populations occupy in a community. Example: Different species of cichlid fish are endemic to the African great lakes and these come in different forms and behaviours that are in line with their specific productive roles in the given environment.

Genetic Factors

Variations in chromosomes and polyploidy cause reproductive isolation and promote the process of speciation. Other reasons for isolation arise from studying genetic distances due to the accumulated mutations in the ability to reproduce with a different population successfully.

Environmental Changes

Environmental shocks, which include climate change and habitat destruction. It can introduce new selective forces in species population interaction and affect evolution. A classic example of environmental change is the peppered moth during the Industrial Revolution in England. As pollution darkened tree trunks, darker colored moths survived and lighter ones died.

Recommended Video for Reproductive Isolation

MCQs on Speciation

Q1. Which speciation entails the appearance of a new species within the geographic range?

1. Sympatric speciation

2. Allopatric speciation

3. parapatric speciation

4. Peripatric speciation

Correct answer: 1) Sympatric speciation

Explanation:

Option (1)-Speciation happens when two populations of identical species live together without interbreeding is known as sympatric speciation. The development of new species occurs within the geographic range of the parental population.

Option (2)- Allopatric speciation occurs when geographical changes cause biological populations of the same species to become isolated from one another.

Option (3)- Two or more new species can arise from one common ancestor through a process known as parapatric speciation.

Hence, the correct answer is option 1) Sympatric speciation.

Q2. Which of the following statements is true about allopatric speciation?

I. Speciation isolates the population by geographic barriers

II. Physical isolation can emerge from animal and plant movements

III. Genetic divergence effects in reproductive compatibility

IV. It emerges only at the boundaries of the parent population

1. I and II

2. I and III

3. II and III

4. II and IV

Correct answer: 1) I and II

Explanation:

Statement I and II are true about allopatric speciation

Geographical barriers play a role in allopatric speciation because they physically separate populations. Physical isolation can also emerge from animal and plant movements. Genetic drift may cause unintentional variations in gene pools.

Statements III and IV are wrong.

Allopatric speciation does not take place at the boundaries of the parent population. Genetic divergence effects in reproductive incompatibility in allopatric speciation.

Hence, the correct answer is option 1) I and II.

Q3. Which hypothesis of speciation does not call on the reinforcing process?

1. Sympatric speciation

2. Allopatric speciation

3. Parapatric speciation

4. Peripatric speciation

Correct answer: 2) Allopatric speciation

Explanation:

The allopatric speciation theory does not necessitate the involvement of the reinforcing process.

Allopatric speciation transpires when distinct groups of a single species are geographically disconnected, which in turn induces genetic divergence due to isolation over a prolonged period. This divergence results in reproductive isolation, which is not contingent upon reinforcement. Reinforcement pertains to the evolutionary process that enhances reproductive barriers when two previously isolated populations encounter secondary contact, typically observed in sympatric or parapatric speciation scenarios where proximity may lead to hybridization.

In contrast, allopatric speciation's emphasis lies in the separation and divergence of genetic traits without dependence on reinforcement mechanisms. The primary focus is the natural divergence that arises from geographic isolation, which is sufficient for the formation of new species.

Hence, the correct answer is option 2) Allopatric speciation.

Also Read:

• MCQs on Speciation & Its Types

• Evidence of Evolution

• Theories of Evolution