Evolution: History, Genes, Heredity & Examples

Evolution refers to a theory describing the growth and the change in the characteristics of a species as it moves from generation to generation. The growth of the species depends on the natural selection process of organisms. 

• Evolution is the study of the characteristics of heredity.
• It uses the concept of natural selection and genetic drift variation.
• The process explains certain theories regarding natural occurrences.
• Charles Darwin and Alfred Russel Wallace proposed the theory of evolution.
• It analyses variations in traits like colour and size.
• Evolution gave rise to the concept of biodiversity.
• Big Bang theory explained the concept of the origin of life.
• According to the theory, the universe was formed by the explosion that took place 20 billion ago.

Read More: Darwin's Contributions - Theory of Evolution

Key Terms: Evolution, Organisms, Biodiversity, Earth, Species, Plants, Animals, Genetic Variation, Mutation, Natural Selection, Genes, Heredity, Population​

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What is evolution?

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Evolution is a biological hypothesis that describes the change in the features of a species of plants, animals, and other living things from generation to generation as a result of natural selection.

• The genes are passed down from parents to offspring during reproduction.
• Genetic variation or mutation are features in a particular population of animals.
• These features tend to grow more common or rare in a given group of species over time.
• Evolution is the study of the spread of alleles, variants, trait values, or character states.
• It is a fundamental milestone in the field of biological theory.

Evolution of Human Life

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History of Evolution

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'Charles Darwin' and 'Alfred Russel Wallace' pioneered the scientific hypothesis of evolution through natural selection in the 19th century. The proposed hypothesis is also known as Darwin's Theory of Evolution.

• Darwin even authored an evolution book called 'On the Origin of Species.'
• According to the theory, offspring are frequently produced in greater numbers, having a low survival rate.
• The earliest theory was proposed in 1744-1829 by Jean Baptiste Lamarck.
• He proposed the hypothesis of 'Transmutation of species.'
• Pre-socratic Greek philosophers also made contributions to the field of evolution.
• Empedocles and Anaximander believed that a certain form of the organism may descend from another.
• These ideas were carried on until the period of the Romans.
• During the Middle Ages, people followed Aristotle's conceptions.
• They believed that whatever was existing in nature had something to do with god.
• As a result, this understanding was classified as Christian Learning.
• However, Aristotle's suggested how new forms of living creatures could arise were still considered.
• This followed the pre-Darwinian period, wherein people accepted physical law for natural events.
• John Ray coined the term "species" to describe some stable natural forms.
• Carl Linnaeus created biological categorization in the year 1735.
• Later, Erasmus Darwin proposed that all warm-blooded animals descended from a single microbe.

Read More: Evolution Class 12 Biology Mendelian Genetics

The current pattern of biodiversity is divided into three categories:

• Speciation (formation of new species over time )
• Anagenesis (changes that occur within a particular species with respect to each passing generation)
• Extinction of species (loss of any particular species with time, as in the case of dinosaurs)

With the help of evolution, three things have been noted, which are as follows:

• Each species' traits differ in physiology, behaviour, and morphology.
• The reproduction and survival rate of a species is determined by the trait that is passed on from one generation to another.
• Characteristics and traits can be transferred from one generation to the next.

Timeline of Evolution

Read More: Difference between Dominant and Recessive Traits

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Role of Genes in Evolution

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The process of evolution occurs at the genetic level. Genes are the fundamental unit of inheritance. DNA is the building block of genes, and any alterations in the sequence of DNA alter the way in which these genes are expressed. 

• When two different species share comparable DNA and genes, they might have common ancestors.
• Our ancestors' histories and evolutionary data are encoded in our DNA. 
• Humans, for example, are believed to have evolved from apes. 
• The DNA undergoes modifications over time.
• While certain modifications are helpful to living beings by helping them adapt to their environment.
• Others can be quite destructive, especially if a fault is involved in the evolution of DNA.
• This defect can be passed along through various generations. 
• The rest of the genes remain unchanged during evolution.

Structure of DNA

Read More: Acquired and Inherited Traits

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Mechanism of Evolution

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The mechanism of evolution is divided into four key phase that cause changes in the gene. The four phases of evolution are as follows:

Mutation

Mutation is defined as the process of change in the DNA sequence occurring in the germ cell. It is the ultimate source of genetic variation. The sperm are passed on to the future generations.

• Mutations make duplicate copies of large sections of the chromosome.
• During the process, half of the protein-coding genes are harmful.
• It will create extra copies of genes found in the genome.
• They are affected by environmental factors such as ultraviolet radiation. 

Read More: Difference Between Autosomes and Allosomes

Heredity

Heredity refers to the transfer of physical and mental characteristics from one generation to another through genes. It is majorly determined by two major factors: genotype and phenotype.

• Characteristics of individuals influenced by genes are known as genotypes. 
• Some of a person's facial traits and eye colour, for instance, are inherited from their parents. 
• For instance, we might have seen people with blue eyes. 
• The blue eye characteristic of a person is inherited from parents having blue-coloured eyes.
• Phenotype refers to an individual's characteristics in relation to the interaction between their genotype and their environment. 
• There is a strong interaction between genes and the environment. 
• The environment and other factors affect an organism's behaviour and looks.

Heredity

Gene Flow

Gene Flow refers to the process of an individual transporting their genetic material from one population to another. It is also known as migration. For instance, a marriage between two individuals of varying ethnicity and race might result in a kid with characteristics acquired from both of the parents. 

• Pollen migrating from one location to another also causes gene flow. 
• Hybrid creatures are formed due to the gene transfer between any two species.

The process of migration takes place mainly in two ways:

Vertical Gene Transfer

Vertical gene transfer occurs when gene flow occurs between the same species and is carried forward through the reproduction process. This results in a vertical gene transfer or gene flow from parents to their children.

Horizontal Gene Transfer

Horizontal gene transfer is the transmission of genes between two different species. This includes the cases when genes are transferred from lower species to higher ones or from symbiotic organisms to the host.

Gene Flow

Read More: Difference Between Gene and DNA

Natural Selection

Natural selection is an important evolutionary mechanism stating that organisms are well-adapted to their surroundings. They have a better chance of survival than the others.

• They are more likely to pass on the traits that helped them survive to the next generation.
• The process is beneficial for the survival of the future generations.
• In this phase, more number of offspring are produced.
• It depends upon the evolutionary fitness of an organism.

Evolution through natural selection of moths

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LUCA

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LUCA is also known as the Last Universal Common Ancestor. It is an organism or a collection of organisms from which all the life presently surviving on Earth descended. The true shape of LUCA cannot be deduced from fossils.

• It has been inferred through phylogenetic bracketing that LUCA is a unicellular organism. 
• LUCA refers to the one among many organisms that existed on the Earth in the very beginning.
• It was most likely an extremophile living near the terrible volcanic vents of the ancient oceans.
• The organism did not require oxygen to thrive (anaerobic) and could produce its own food (autotrophic). 
• From an evolutionary standpoint, it represents a watershed moment in the evolution of life on Earth. 
• The proof of LUCA's existence can be seen in the genes of modern creatures.

Read More: Important Principles of Inheritance and Variation

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Evolution of Life on Earth

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Many creatures have evolved, survived, and become extinct over the Earth's 4.5 billion-year history. More than 99 percent of all life on Earth is already gone, according to various studies. 

• The true genesis of life, however still remains unknown. 
• Microbial fossils are one of the oldest known fossils, dating back 3.4 billion years. 
• The current scientific agreement on the beginning of life is that it began with self-replicating molecules.
• It later evolved into the complex biochemistry of life that exists today. 

Some of the attempts made to explain the very first origins of life are:

• Abiogenesis
• Clay Hypothesis
• Deep-Sea Vent Hypothesis
• Miller Urey Experiment
• Panspermia
• RNA World Hypothesis

Read More:Inheritance

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Things to Remember

• Evolution refers to the growth and the change in the characteristics of a species
• It moves from generation to generation.
• DNA is the building block of genes.
• Any alterations in the sequence of DNA alter its content as well as the way in which these genes are expressed.
• Heredity refers to the transfer of physical and mental characteristics from one generation to another.
• Gene Flow refers to the process of transporting genetic material from one population to another.
• LUCA refers to one among many organisms that existed on the Earth in the very beginning.

Read More: Incomplete dominance

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Previous Year Questions

1. Transformation of the early reducing atmosphere of the earth into an oxidizing atmosphere was mainly due to the activities of...[KCET 2008]
2. The brain capacity of Homo habilis...[KCET 2019]
3. According to Darwin, evolution is_______...[KCET 2010]
4. By the statement "Survival of the Fittest" Darwin meant that...............[KCET 2011]
5. The idea of Natural Selection as the fundamental process of evolutionary changes was reached….[KCET 2007]
6. Coarcervates were experimentally produced by,…..[KCET 2004]
7. Find the mis-match from the following pairs :….[KCET 2016]
8. Which among the following was the biggest land dinosaur?...[KCET 2020]
9. A good example for recapitulation theory is/are​
10. Which one of the following organs are homologous?​
11. An experiment to prove that organic compounds were the basis of life was performed by: