Evolution Meaning and Types

On our planet Earth, the evolution of life occurred many decades ago by a complex process. There are different interpretations of evolutionary theories. The evolution of life on Earth conveys the origin of the Earth and the lives on Earth. It also explains the theory of the existence of the world and the increase in biodiversity of the Earth.

Introduction:

We all have heard people normally saying “humans come from monkeys” whenever a child jumps around or eats a lot of bananas.
Have you ever thought if this statement is actually true or just an equivocate?
Oh!! A question just popped in my mind, if monkeys are the ancestors of humans, do all plants, animals, insects that we see around also have some ancestor.
We are going to find answers to these questions in this chapter.
Evolution - study of slow,continuous, and irreversible change in different species from simple to complex beings in order to become better adapted towards the changing environment.
As stated by Theodosius Dobzhansky “ Nothing in biology makes sense except in the light of evolution”

Table of Contents:

What is Evolution?
The Big Bang Theory
Mechanism of Evolution
Mutations
Gene Flow
Genetic Drift
Natural Selection

What is Evolution?

Evolution refers to the path or process by which modern organisms descended from their predecessors or ancestors, along with the changes or modifications in the frequencies of alleles. Evolution is a theory that explains the changes in the characteristics of animals, plants and other living things on the earth. There are different species of organisms in a population because of genetic variation and mutation. However, these changes or modulations become common or rare among the population.

The Big Bang Theory

Among many scientists and researchers, the most acceptable theory of the origin of life is the big bang theory. According to the theory, the universe and other planets are the result of a big explosion that took place over 20 billion years ago. Life on Earth probably occurred 10 billion years after the big bang explosion.

It is believed that the first living cell originated from a non-cellular molecule. This cell further divides and evolves with new characteristic features of survival. These cells adapt the light energy and release oxygen from the cells.

The multicellular organisms evolved faster, and new organisms, such as plants, invertebrates, animals, etc, evolved over time. Further, these organisms evolve in their own community and develop in a large population. However, climate change, environmental conditions and other factors played a significant role in their survival.

During evolution, one organism dominated over another in such a way that natural selection is called the survival of the fittest. It is believed that the evolution of animals started with jawless fish. Later Dinosaurs, which are known as land reptiles, existed. Followed by reptiles, mammals dominated other species on the Earth.

Mechanism of Evolution

The evolution of new species takes place because of the changes or modifications in the gene pool, which is a collection of genes. The following mechanisms are key factors for the changes in the genes of the population. They are:

Mutation
Gene Flow
Genetic Drift
Natural Selection

Mutations

Mutation refers to the changes in the sequence of the DNA of an organism. It takes place in the germ cells, such as sperm or egg cells. Thus, the changes can pass on to future generations. The mutation is inherited from the parents, which can lead to evolution. These changes in DNA sequence are caused because of environmental changes and other factors such as ultraviolet radiation. However, acquired mutations do not pass on to future generations and are not involved in evolution.

Gene Flow

Gene flow refers to the transfer of genes from one population to another. The transfer of pollen from one place to another by wind or other pollinating agents is an example of gene flow. When a person from one country mates with another person from a different country, gene flow occurs between the individuals. Gene flows across different populations, and also gene is transferred horizontally, which is genetic material transferred through asexual means. Example: Prokaryotes.

Genetic Drift

Genetic drift refers to changes in the frequencies of alleles of a population. This is a random event that can affect small populations. Examples of genetic drift are the bottleneck effect and the founder effect.

Bottleneck Effect: This effect takes place when there is a sudden decrease in the population because of factors such as natural calamities. Some genes are depleted, resulting in a drastic reduction in genetic diversity.
Founder Effect: In a large population, a small number of individuals are isolated to form a new population, then there is a loss of genetic diversity in the new population. Thus, some genetic traits become more dominant, such as genetic diseases for future generations.

Natural Selection

In some individuals, the survival and reproductive rate are higher. Thus, they transfer these genetic features to their offspring creating change in future generations. The selection of genetic qualities can increase the survival rate in future generations, which is called natural selection.

Practice Problems

Q1. Which of the following effects occurs when there is a sudden decrease in the population?

a. Bottleneck Effect
b. Founder Effect
c. Brownian effect
d. None of the above

Answer: a. Bottleneck effect

Explanation: It takes place when there is a sudden decrease in the population because of factors such as natural calamities. Some genes are depleted, resulting in a drastic reduction in the genetic diversity.

Q2. Which of the following effects results in loss of genetic diversity in the new population?

a. Bottleneck Effect
b. Founder Effect
c. Brownian effect
d. None of the above

Answer: b. Founder effect

Explanation: In a large population, a small number of individuals are isolated to form a new population, then there is a loss of genetic diversity in the new population.

Q3. Which of the following refers to the transfer of genes from one population to another?

a. Mutations
b. Gene Flow
c. Genetic Drift
d. Natural Selection

Answer: b. Gene Flow

Explanation: Gene flow refers to the transfer of genes from one population to another. The transfer of pollen from one place to another by wind or other pollinating agents is an example of gene flow.

Frequently Asked Questions

Q1. What is Hardy-Weinberg Equilibrium?
Answer: The Hardy-Weinberg Equilibrium is expressed in the mathematical equation to calculate the genetic variation of the population at equilibrium. Thus, the Hardy-Weinberg Equation can be expressed as: p² + q² + 2pq = 1

Q2. What is an Allele?
Answer: An allele is defined as a version of forms of a gene. It is used to describe the variations in the gene. A person inherits one allele from each parent.Q3. Where does mutation occur?
Answer: Mutation takes place in the germ cells, such as sperm or egg cells. Thus, the changes can pass on to future generations.

QUIZ

Q1.Which of the following is the correct sequence of events in the origin of life?
1. Formation of protobionts
2. Synthesis of organic monomers
3. Synthesis of organic polymers
4. Formation of DNA-based genetic systems

(a) II, III, I, IV
(b) II, III, IV, I
(c) I, II, III, IV
(d) I, III, II, IV

Q2. The similarity of bone structure in the forelimbs of many vertebrates is an example of -
(a) Convergent evolution
(b) Analogy
(c) Homology
(d) Adaptive radiation

Q3. According to Hugo de Vries, the mechanism of evolution is -
(a) Phenotypic variation
(b) Saltation
(c) Multiple step mutations
(d) Minor mutations

Q4. In Hardy-Weinberg equation, the frequency of heterozygous individual is represented by -
(a) Pq
(b) q2
(c) P2
(d) 2pq

Q5. Genetic drift operates in -
(a) Non-reproductive population
(b) Slow reproductive population
(c) Small isolated population
(d) Large isolated population

Q6. Industrial melanism is an example of -
(a) Neo Lamarckism
(b) Neo Darwinism
(c) Natural selection
(d) Mutation

Q7. Variations caused by mutation, as proposed by Hugo de Vries are -
(a) Random and directional
(b) Random and directionless
(c) Small and directional
(d) Small and directionless

Q8. Which of the following had the smallest brain capacity?
(a) Homo sapiens
(b) Homo neanderthalensis
(c) Homo habilis
(d) Homo erectus

Q9. The chronological order of human evolution from early to recent is -
(a) Ramapithecus → Homo habilis → Autralopithecus → Homo erectus
(b) Australopithecus → Homo habilis → Ramapithecus → Homo erectus
(c) Australopithecus → Ramapithecus → Homo habilis → Homo erectus
(d) Ramapithecus → Australopithecus → Homo habilis → Homo erectus

Q10. S.L.Miller, an American scientist, created an electric discharge experiment in a closed flask containing CH4, H2, NH3 and water vapor at what temperature?
(a) 400° C
(b) 800° C
(c) 200° C
(d) 1000° C