Evolution

Evolution is a theory in Biology that explains the changes in flora, fauna, and other living things on Earth and that this depends on the process of evolution. At the time of birth, the genes are passed on from parent to offspring. Factors are a manifestation of these genes. Different characteristics exist in a given number of species due to genetic variation or due to mutations. Over time, these traits become more common or less common in certain species of animals. Evolution is one of the most important topics in biology. The chapter carries a weightage of 6% of the total marks in NEET and 4-5% of the weightage of other entrance exams like Paramedical and Pharmacy.

Important Topics of Evolution

• Theories of Evolution
• Evidence of Evolution
• Darwin's Theory of Natural Selection
• Evolution and Hardy Weinberg Principles
• Mutation Theory

Overview of the Chapter

Evolution is the prerequisite process by which species will change with time through variations in their genetic makeup. This is one of the basic concepts in biology explaining diverse life on earth. Before Darwin, there existed ideas on evolution but they needed to be clearly explained. Early ideas advanced by Lamarck and contemporaries held that an organism could change in its lifetime and transmit such changes to its offspring.

The English naturalist Charles Darwin provided another scientific explanation of the emergence of life through his theory of evolution by natural selection. The work gave a scientific explanation of how species evolve, influencing countless biological disciplines and giving insight into the interrelationship of all life forms.

Historical Context of Evolution

Any species that exists today on Earth has the Last Universal Common Ancestor (LUCA) that used to live about 3.5 billion to 4 billion years ago. This can also be explored by studying the fossil records that usually include Biogenic Graphite in living things or other evolutionary data incorporated into each passing generation that can provide details about almost every living thing in history. Some major events are discussed below:

Also Read:

• Evolution MCQs

• Natural Selection

• Evolution by Stages

• Human Health And Disease

Darwin's Theory of Evolution

Darwin's proposed natural selection theory has four main components:

• Inheritance: a few aspects are permanently transferred from parent to children while a few factors have an environmental impact and Habitat.

• Variety: Even within the same population each person exhibits different differences such as colour, body size, features, etc. although they are of the same type.

• High rate of population growth: Few species have more children each year than the number of resources available to them. This leads to a resource struggle between people.

• Different survival and reproduction: Those creatures with a genetic predisposition to survival will lead to reproduction and thus provide additional offspring for future generations.

We can therefore say that with each passing generation, the offspring usually survives the genetic predisposition of the parents and alters their traits and characteristics with certain natural conditions which usually enable them to adapt to a particular given habitat. This is how an evolution evolved from one generation to another.

NCERT Exemplar Solutions Subject-wise link:

• NCERT exemplar solutions for class 12 Physics

• NCERT exemplar solutions for class 12 Chemistry

• NCERT exemplar solutions for class 12 Mathematics

• NCERT exemplar solutions for class 12 Biology

Evidence for Darwin's Theory

The theory of evolution is overwhelmingly supported by a huge amount of evidence from many very different fields of science.

Fossil Record

• Fossils offer a chronological record of the life of the past:

• Fossils show changes in species over time and transitional forms that link major groups.

• Archaeopteryx, a transitional fossil between dinosaurs and birds, and the many hominid fossils tracing human evolution.

Comparative Anatomy

Comparative anatomy examines the anatomy of diverse species and looks for evidence of both similarities and differences:

Homologous Structures

Structures are shared in different species because they have evolved from a common ancestor. A good example is the forelimbs of mammals.

Analogous Structures

Structures that serve a similar function but of different origins, like the wings of birds and insects.

Molecular Biology

Molecular biology includes genetic material to reveal evolutionary relationships:

DNA Sequencing

This carries genetic similarities and dissimilarities among species, thus proving common ancestry.

Examples

Genetic closeness of human beings with chimpanzees, and conserved sequences of crucial genes in all species.

Biogeography

Biogeography is the study of the geographic distribution of species :

Distribution Across the Globe

The geographic distribution of species reflects evolution; for example, unique species on islands from common ancestors.

Examples

Variations of finches on the Galapagos Islands and the distribution of marsupials in Australia.

NCERT Solutions Subject-wise link:

• NCERT solutions for class 12 Physics

• NCERT solutions for class 12 Chemistry

• NCERT solutions for class 12 Mathematics

• NCERT solutions for class 12 Biology

Causes of Evolution

Evolution is a result of several factors that introduce and propagate genetic variations in populations.

Role of Genes in Evolution

The Evolution process takes place at the Genomic level. Genetics are the basic unit of inheritance. Gene is made up of DNA. Any changes in the DNA sequence will affect the structure and affect the way genes are expressed. Our ancestral history and evolutionary data are embedded in DNA. Some of the important points are discussed below:

• Some important traits are passed from parent to offspring. These are also influenced by environmental factors and habitat.

• Individuals show variation in population such as color, body size, and other characteristics even though they belong to the same species.

• Some species reproduce at a higher rate than the available resources which leads to competition for survival.

• Organisms with better traits are selected naturally for survival and are more likely to reproduce and take advantage of traits to the Future generations.

Heredity

Genotype - Genetics depends on two key factors, namely Genotype and Phenotype. Certain aspects are controlled by Gene. This is called a Genotype. For example, some of the facial features, hair type and eye colour are inherited from one of the parents.

To be precise, if one of the parents has a blue eye colour and he/she is inherited from the offspring then it is called the 'blue eye feature'.

Phenotype - The set of human traits concerning their interactions between their genotype and environment is called Phenotype. Because of this feature, many aspects of human phenotype are not inherited. Phenotype appears naturally.

There is a strong combination of Genes and nature that expresses the appearance and behaviour of living things. Various examples can be counted on that, from the size of the bird's beak, the lashes on the animal's back, the colour of the hair, etc.

NCERT Books Link:

• NCERT book for class 11 Biology.

• NCERT book for class 12 Biology

Gene Flow

The flow of genes is also called migration. This is nothing more than carrying a human gene from one figure to another. This migration occurs through several factors such as pollination flying from one place to another, and mating between people of different races and ethnicities will produce offspring bearing the characteristics of both parents. The genetic flow between different species occurs in two ways;

• Vertical genetic transfer: The flow of genes between two genes of the same species is affected by migration and further reproduction, thus the transfer of genes from parents to offspring occurs.

• Horizontal gene transfer: This is a genetic transfer between two different types. Genetics can be transferred from the lower extremities to the upper extremities or genetic transfer occurs from the Endosymbiont to the host.

Genetic diversity depends on the flow of genes. The flow of genes can be prevented between certain species of animals by placing barriers between isolated populations and thus preserving the unique identity of a specific population.

Mutation

• Mutations are random changes of DNA.

• They represent the ultimate source of genetic variation, providing new traits on which natural selection can then act.

Types

• Point mutations: Change in a single nucleotide

• Chromosomal mutations: Change in the number or structure of chromosomes.

NCERT Notes Subject Wise Link:

• NCERT notes Class 12 Maths

• NCERT notes Class 12 Physics

• NCERT notes Class 12 Chemistry

• NCERT notes Class 12 Biology

Types of Questions Asked and Weightage from Evolution

During the preparation of the exam, there are different types of questions asked about Evolution in different forms. The table given below contains the different patterns of questions asked in different exams.

Tips, Tricks, and Strategies for Evolution

It's hard to remember everything in a single go. We made the entire problem easy. Some of the tricks regarding Evolution are given below which you can use to memorize the important points.

Darwin's Theory of Natural Selection

"VSRF: Variation, Struggle, Reproduction, Fitness"

• V: Variation (differences within species)

• S: Struggle for existence (competition for resources)

• R: Reproduction (organisms with favorable traits reproduce more)

• F: Fitness (better-adapted organisms survive and pass on traits)

Evidences of Evolution

"FAME: Fossils, Anatomy, Molecular, Embryology"

• F: Fossils (show evolutionary changes over time)

• A: Anatomy (homologous and analogous structures)

• M: Molecular evidence (DNA and protein comparisons)

• E: Embryology (similar development in embryos of different species)

Hardy-Weinberg Principle

"ALEF: Allele, Large, Equilibrium, Frequency"

• A: Allele frequencies remain constant in a population if no evolution occurs

• L: Large population size (minimizes genetic drift)

• E: Equilibrium (no evolution without external influences)

• F: Frequency of alleles remains stable

Types of Natural Selection

"DSS: Directional, Stabilizing, Disruptive"

• D: Directional selection

• S: Stabilizing selection

• S: Disruptive selection

Genetic Drift

"BF: Bottleneck, Founder Effect"

• B: Bottleneck effect

• F: Founder effect

Speciation

"AIR: Allopatric, Isolation, Reproductive barriers"

• A: Allopatric speciation

• I: Isolation

• R: Reproductive barriers

Convergent and Divergent Evolution

"CAD: Convergent, Analogous, Divergent"

• C: Convergent evolution

• A: Analogous structures

• D: Divergent evolution

Adaptive Radiation

"FEAD: Finches, Environment, Adaptation, Diversification"

• F: Finches

• E: Environment

• A: Adaptation

• D: Diversification

Prescribed Books for Evolution

NCERT Biology textbook class 11 forms the base for learning Evolution. Further extended understanding of the concept can be done through "Trueman's Elementary Biology, Volume 2", which provides all essential explanations with practice questions. Another helpful book is "Pradeep's Biology" which provides proper explanations with solved examples. Other great videos, articles, and practice mock tests are available on the Careers360 website for this topic.

Also Read

Recommended Video on Evolution