Human beings have always been perplexed about the origin and evolution of life on earth. For centuries, a number of theories and hypothesis have been suggested to explain the evolutionary process.
In the previous year, in a very short time life was created by some supernatural power. Most of the religions and civilizations still believe in it, however, they do not have a scientific explanation and more a matter of faith. There has always been an attempt by the scientists and naturalists with keen observation, to explain the evolution scientifically and to look for its evidences.
The process of evolution involves a gradual change or variation in the organisms generation after generation. It means that the organisms of present-day have arisen from ancestors that were simpler in an organisation.
human evolution, origin of life, big bang theory, theories on origin of life, evolution of life forms, experimental evidence on theory of chemical evolution, evidences of evolution, homology and analogy, biochemical and biogeographical evidences, adaptive radiation, lamarck's theory of evolution, darwins theory of evolution, mechanism of evolution, hardy weinberg principle, mutations
human evolution, origin of life, big bang theory, theories on origin of life, evolution of life forms, experimental evidence on theory of chemical evolution, evidences of evolution, homology and analogy, biochemical and biogeographical evidences, adaptive radiation, lamarck's theory of evolution, darwins theory of evolution, mechanism of evolution, hardy weinberg principle, mutations
I: Evolution
If I have seen further it is by standing on the shoulders of Giants.
-- Sir Isaac Newton
1
Theories in Science
In the context of scientific inquiry, a theory is:
A conceptual framework supported by a large body of evidence
Broader in scope than a hypothesis. A theory ties information together and leads to specific testable hypotheses
In other words, a theory is a big deal in science, NOT a synonym for guessing
2
2
3
(This used to be a joke, but I’m not laughing anymore.)
3
Historical Overview
What can explain both the unity and diversity of life on Earth?
Organic evolution: genetically based change over time. It acts on individuals in the present, but only manifests in the population over generations.
Natural Selection: mechanism causing the match between organisms and their environment (adaptive evolution = adaptation)
4
4
Traditional views involved unchanging and perfect species inhabiting a young Earth (Old Testament, Linnaeus, etc.)
The emergence of paleontology and geology helped lay the groundwork for Darwin’s contributions
Other areas of research also influenced his thinking, including studies on human population growth
6
6
Fig. 22-2
American Revolution
French Revolution
U.S. Civil War
1900
1850
1800
1750
1795
1809
1798
1830
1831–1836
1837
1859
1837
1844
1858
The Origin of Species is published.
Wallace sends his hypothesis to Darwin.
Darwin begins his notebooks.
Darwin writes essay on descent with modification.
Darwin travels around the world on HMS Beagle.
Malthus publishes “Essay on the Principle of Population.”
Lyell publishes Principles of Geology.
Lamarck publishes his hypothesis of evolution.
Hutton proposes his theory of gradualism.
Linnaeus (classification)
Cuvier (fossils, extinction)
Malthus (population limits)
Lamarck (species can change)
Hutton (gradual geologic change)
Lyell (modern geology)
Darwin (evolution, natural selection)
Wallace (evolution, natural selection)
7
7
Younger stratum
with more recent
fossils
Layers of deposited
sediment
Older stratum
with older fossils
8
8
Several 18th century naturalists (including Erasmus Darwin) suggested life evolves as environments change
Jean-Baptiste Lamarck hypothesized that species evolve through use and disuse of body parts and subsequent inheritance of acquired characteristics
This mechanism is unsupported by evidence (e.g., even if you and your mate lost the same finger, your children would still be born with all ten), but it did refocus subsequent research
Lamarck’s Hypothesis
9
9
10
The miniature phenotype of Bonsai trees is caused by manipulations of a bonsai master, not genetics. Would the next generation still be stunted if we planted their seeds and allowed them to grow naturally?
11
12
After first studying medicine, then theology at Cambridge, Darwin took an unpaid position as naturalist for a 5-year voyage around the world
During his travels on HMS Beagle, he collected thousa ...
The stem bears leaves, buds, flowers & fruits & helps to spread them out so that they can function properly. For example, it helps to spread out the leaves in such a way that they get the maximum possible sunlight and air..
It is a type of cyclic flow of nutrients between non- living components like soil, rock air and water and living organisms and micro oganism (Pseudomonas and Aeruginosa). It makes the biosphere dynamic. In oxygen cycle there is a cyclic flow of atmospheric oxygen. Photosynthesis releases oxygen in the atmosphere. Respiration absorbs oxygen. By photosynthesis plant produces organic molecules (C6 H12 O6). By respiration that organic molecule is oxidized to release energy and carbon oxide.
I: Evolution
If I have seen further it is by standing on the shoulders of Giants.
-- Sir Isaac Newton
1
Theories in Science
In the context of scientific inquiry, a theory is:
A conceptual framework supported by a large body of evidence
Broader in scope than a hypothesis. A theory ties information together and leads to specific testable hypotheses
In other words, a theory is a big deal in science, NOT a synonym for guessing
2
2
3
(This used to be a joke, but I’m not laughing anymore.)
3
Historical Overview
What can explain both the unity and diversity of life on Earth?
Organic evolution: genetically based change over time. It acts on individuals in the present, but only manifests in the population over generations.
Natural Selection: mechanism causing the match between organisms and their environment (adaptive evolution = adaptation)
4
4
Traditional views involved unchanging and perfect species inhabiting a young Earth (Old Testament, Linnaeus, etc.)
The emergence of paleontology and geology helped lay the groundwork for Darwin’s contributions
Other areas of research also influenced his thinking, including studies on human population growth
6
6
Fig. 22-2
American Revolution
French Revolution
U.S. Civil War
1900
1850
1800
1750
1795
1809
1798
1830
1831–1836
1837
1859
1837
1844
1858
The Origin of Species is published.
Wallace sends his hypothesis to Darwin.
Darwin begins his notebooks.
Darwin writes essay on descent with modification.
Darwin travels around the world on HMS Beagle.
Malthus publishes “Essay on the Principle of Population.”
Lyell publishes Principles of Geology.
Lamarck publishes his hypothesis of evolution.
Hutton proposes his theory of gradualism.
Linnaeus (classification)
Cuvier (fossils, extinction)
Malthus (population limits)
Lamarck (species can change)
Hutton (gradual geologic change)
Lyell (modern geology)
Darwin (evolution, natural selection)
Wallace (evolution, natural selection)
7
7
Younger stratum
with more recent
fossils
Layers of deposited
sediment
Older stratum
with older fossils
8
8
Several 18th century naturalists (including Erasmus Darwin) suggested life evolves as environments change
Jean-Baptiste Lamarck hypothesized that species evolve through use and disuse of body parts and subsequent inheritance of acquired characteristics
This mechanism is unsupported by evidence (e.g., even if you and your mate lost the same finger, your children would still be born with all ten), but it did refocus subsequent research
Lamarck’s Hypothesis
9
9
10
The miniature phenotype of Bonsai trees is caused by manipulations of a bonsai master, not genetics. Would the next generation still be stunted if we planted their seeds and allowed them to grow naturally?
11
12
After first studying medicine, then theology at Cambridge, Darwin took an unpaid position as naturalist for a 5-year voyage around the world
During his travels on HMS Beagle, he collected thousa ...
The stem bears leaves, buds, flowers & fruits & helps to spread them out so that they can function properly. For example, it helps to spread out the leaves in such a way that they get the maximum possible sunlight and air..
It is a type of cyclic flow of nutrients between non- living components like soil, rock air and water and living organisms and micro oganism (Pseudomonas and Aeruginosa). It makes the biosphere dynamic. In oxygen cycle there is a cyclic flow of atmospheric oxygen. Photosynthesis releases oxygen in the atmosphere. Respiration absorbs oxygen. By photosynthesis plant produces organic molecules (C6 H12 O6). By respiration that organic molecule is oxidized to release energy and carbon oxide.
Intestine part of the alimentary canal is prone to many infections which we term as nutritional diseases which may lead to its inflammation. The various infectious agents causing nutritional disorders are bacteria, virus, tapeworms, roundworms, threadworms, hookworm, pin worm etc. Here are some common nutritional diseases or disorders of the digestive system (marasmus)
INTRODUCTION OF ALTERNATIVE SOURCES OF ENERGY: We know that by the time conventional sources of energy will deplete soon due to improved technological progress and increased demand. To cater the rising demand, keeping a balance with limited with limited availability of conventional sources is very important. It is mandatory to look up to the alternative sources of energy which we also term as non-conventional sources of energy.
We perform many activities consciously or unconsciously, for example, when we eat food, our eyes help to locate the food, the nose smells it, hands bring food to the mouth, teeth chew and masticate it, the tongue pushes the food inside the alimentary canal, and so on. (NERVOUS SYSTEM FUNCTION) All these activities occur in a coordinate manner. The organ system in our body that brings about coordination and integration of body activities, is the nervous system.
LIKE BEGETS LIKE, which means young one resemble their parents, (MONOHYBRID CROSS & DIHYBRID CROSS) is the well-known dogma associated with heredity. Each species has similarities among themselves due to the cause of heredity. W.Bateson was the first one to coin the term genetics in 1905. It is derived from the greek word “genesis” means to grow into or to become . in other word, genetics is the study of heredity and variation.
Flowers are the reproductive parts of plants,which are responsible for the production of gametes or sex cells ((non flowering plants).
A flower is modified shoot in which the leaves are modified into floral parts. A blossom propagates a branch from a bud in the axil of a little leaf-like structure called the bract. A bract is commonly green due to presence of chlorophyll and is a very small structure (non flowering plants).
Events of fertilization
A] Pollination brings female and male gametophyte together- The male and female gametophytes must meet and unite their gametes to fertilize egg. This is done by pollination, in which pollen is placed on the stigma of the carpel.
B] Germination of pollen grain under suitable condition- The cytoplasm of the pollen grain absorbs sugar and water from the stigma and bulges out to produce a tube known as pollen tube by braking down exine of pollen grains. This germinating pollen tube grows down through the stigma and style of flower towards the micropyle of the ovary. This tube produces chemical, calcium such as that dissolves the tissues of the style and the tip of the pollen tube enters the ovary through the micropylar end occurring double fertilization.
The eyeball is a spherical structure having 2.5 diameters. Structurally, the eyeball has three layers:- sclerotic layer (outer layer); choroid (middle layer) and retina (inner layer).
Outermost layer contains sclera and cornea
Middle layer contains choroid, ciliary body and iris.
Innermost layer consists of retina
It is a group of viruses that causes respiratory problems in animals and birds. Some viruses are not so dangerous, but due to biological reasons, some family members become lethal causing even death e.g. SARS (Severe acute respiratory syndrome)
MERS (Middle-east respiratory syndrome)
If we see at the sky for some time at night, then we will observe some stars forming groups with shapes. So, the shape formed by the group of stars is called a constellation diagram. The shapes of constellations resemble objects familiar to those people. Each constellation is signified by an animal, a human being, or some other objects it appears to resemble. All the constellations seem to move in the sky from east to west. This is due to the rotation of the earth on its axis from west to east.
The disease is the malfunctioning of the body organs due to one reason or the other. In other words, it is a disorder of the body. The state of the body when any of its normal functions are disturbed or when the structures are altered is called disease. We understand that to remain healthy, we need to do much more than just keep away from disease. CONGENITAL DISEASE: This type of disease is present right from the birth. This is caused either due to genetic disorders or gene mutation or environmental factors. These diseases are passed on from one generation to next generation. Some examples of congenital diseases are Haemophilia, Sickle cell anaemia, Colour blindness, Thalassaemia etc.
All living organisms are made up of a variety of body parts like roots, leaves, flowers, fruits, wood etc. in plants and bones, flesh, nerves etc in animals. These parts look different from each other, yet they are all composed of tiny units called cells. Moreover, many living organisms like Amoeba, Paramecium, Chlamydomonas etc. consist of only one cell.
All living beings are made up of cells. The structural and functional unit of life is a cell which is the building block of the body. New cell arises from the pre-existing cells by the process of cell division.
Cell division occurs in all living organisms. In unicellular organisms, cell division directly produces two individuals. In multicellular organisms or higher-level organisms, life begins from a single cell, as a zygote, whIch divides and redivides mitotically into a number of cells to form a complete organism.
In multicellular organisms, there are two types of cells.
a)The somatic cells or the body cells- They form the body of an organism.
b)The reproductive cells or sex cells- They are gamete-producing cells.
Bacteria are the simplest ,most primitive and unicellular organisms without a true nucleus. That is why they are prokaryotic. they are placed under kingdom Monera. they are found everywhere in air,water,soil,food,inside our body etc. they lack nucleus and other cell organelles of complex cellslike plants,they possess a cell wall. each bacterial cell has its nuclear material in the form of a single chromosome which is not enclosed in a nuclear membrane.
Atoms are too small to see even with a powerful microscope and too light to be weighed even on the most sensitive balance. The history of the discovery of the structure of an atom is fascinating but a complicated subject. Only 100 years ago, scientists believed that atoms were solid, indestructible particles. Since then many great scientists had contributed brilliantly to give us the today’s model of an atom. Over the centuries, many philosophers and scientists tried to develop a model of the atom.
Conduction of water in plants is less elaborate than that of animal as well as plants. Plants are less active, so their cells do not need quick supply of materials. So, the only substances which are to be supplied to a plant through vascular bundle are water and minerals, this process is called ascent of sap. These materials are not available from air. Transport system also helps to carry food prepared in the leaves to the various parts of the plant like stems , roots etc. Ascent of sap is executed by two types of vascular bundles: Xylem which transports water and Phloem which transports prepared food.
On the basis of the function and occurrence ,tissues present in animal body is called animal tissue. These animal tissue is classified into the following four types:
Epithelial tissue
Connective tissue
Muscular tissue
Nervous tissue
The ability of any living organism terms as acclimatization. It develops certain features which improves the chances of its survival in the changing environment. Plants and animals can adopt themselves in such a way that they can easily survive in the conditions where they use to live. We term this phenomenon adaptation also. Acclimatization is a trait of an organism. It favors the living organism by natural selection.
Flowers are the reproductive parts of plants,which are responsible for the production of gametes or sex cells ((non flowering plants).
A flower is modified shoot in which the leaves are modified into floral parts. A blossom propagates a branch from a bud in the axil of a little leaf-like structure called the bract. A bract is commonly green due to presence of chlorophyll and is a very small structure (non flowering plants).
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
1. EVOLUTION NOTES: EASY EXPLANATION
OF ITS THEORY
Spread the love
EVOLUTION NOTES
INTRODUCTION:
Human beings have always been perplexed about the origin and evolution of life on earth. For centuries, a
number of theories and hypothesis have been suggested to explain the evolutionary process.
In the previous year, in a very short time life was created by some supernatural power. Most of the religions
and civilizations still believe in it, however, they do not have a scientific explanation and more a matter of
faith. There has always been an attempt by the scientists and naturalists with keen observation, to explain
the evolution scientifically and to look for its evidences.
The process of evolution involves a gradual change or variation in the organisms generation after
generation. It means that the organisms of present-day have arisen from ancestors that were simpler in an
organisation.
CAUSES: The following are causes of evolution.
1. Variation in the gene pool of members of a population.
2. Natural selection favouring the accumulation of advantageous variations.
Genetic drift or chance selection.
The word evolution has been derived from the Latin word “evolvere” (e: out, Volvo: to roll) means to unroll or
unfold to reveal modifications or gradual changes. Therefore, evolution is defined as a naturally occurring
slow, continuous and irreversible process of change.
THEORIES OF EVOLUTION: From time to time, several theories have been put forth to explain the process
of evolution of plants and animals. Some of these theories are described here.
LAMARCK’S THEORY OF EVOLUTION:
THEORY OF INHERITANCE OF ACQUIRED CHARACTER
One of the first attempts to explain evolution was made by the French Biologist Lamarck in 1809. Lamarck
published his work in a book called “Philosophic Zoologique”. The theory proposed by Lamarck is known as
the “Theory of inheritance of acquired characters” or “Lamarckism”.
TWO ASSUMPTIONS OF HIS THEORY:
USE AND DISUSE OF THE ORGANS OR BODY PARTS:
The organs or body parts of the body which are used more and more, become elongated or increase in size
while the parts that are not used to become weak and smaller and gradually disappear.
INHERITANCE OF ACQUIRED CHARACTERS: The characteristics or changes acquired during the life
time of an organism are transmitted by heredity to the next generation (offspring).
Lamarck believed that new species evolved after a long period of time, after many generations acquiring
new characters and losing the old characters (depending on the use and disuse of organs).
2. EXAMPLES TO SUPPORT LAMARCKISM:
1. Lamarck took the examples of giraffe in support of his theory.
According to Lamarck, there was a time when giraffes were short necked.
When these short necked giraffe did not find any vegetation to feed on the ground, they tried to reach
the upper part of a tree to eat its leaves.
Thus by making continuous efforts, the neck and forelimbs of giraffe started becoming the longer
gradually.
These acquired characters were inherited by the offsprings of the giraffe in successive generations.
After a considerable long period of time, the giraffe evolved having a long neck and longer forelimbs
than hind limbs.
This proves an effect of extra use and lengthening of some organs.
2. Vestigial organs refer to the organ structures that have lost all or most of its original function present
in another species, generally present in rudimentary conditions.
Wisdom teeth and pinnae are other examples of vestigial organs.
EXPERIMENTS BY WEISMANN
Weismann in nineteenth century tested the Lamarck’s theory by cutting off the tails of mice generation after
generation. According to Lamarck’s theory, the subsequent generation should have had the shorted tails but
in Weismann experiments the offsprings of mice whose tails were cut had the tails of the same length.
Weismann continued his experiment for 20 generation but found mice with tails of the same length as the
first generation. He discarded the theory of inheritance of acquired character.
DARWIN’S THEORY OF EVOLUTION BY NATURAL SELCTION.
Charles Darwin, an English naturalist and biologist is well known for his work as a naturalist and his theory on
evolution.
3. He sailed on a survey ship called “HMS Beagle” in 1831 at the young age of 22 years and explored South
America, the Galapagos Islands and other islands in next five years. During this time he studied variety of
animals and collected a great deal of data on variation.
Based on his data, in 1839 Darwin formulated his theory popularly known as “Theory of Natural Selection”
and published his book “The origin of species”.
DARWIN’S THEORY OF EVOLUTION ( EVOLUTION
DEFINITION )
Darwin’s theory of evolution by natural selection can be summarized below:
OVERPRODUCTION: All the organisms produce much more offspring than can actually survive. For
example, a housefly lays thousands of eggs, a fern plant produces millions of spores etc.
STRUGGLE FOR EXISTANCE: Due to over production, there must be a struggle for existence. There is
struggle between the member of same species for food, water, air and other space. Only a few are able
to survive and rest perish or get eliminated.
VARIATIONS EXIST WITHIN A POPULATION: The offsprings of the same parents differ from one
another and show variations. Apart from the visible variations, certain hidden variation also exists.
SURVIVAL OF THE FITTEST OR NATURAL SELECTION: The individuals with favourable variations
survive in the struggle. The organisms with unfavourable variations die out and only the fittest individuals
survive, reproduce and pass their favourable characters to the next generation.
The process of survival of the fittest over many generations slowly increases the proportion of fit individuals
due to heritable favourable variations.
In other words, nature selects the individuals that are well adapted to the environment and allows them to
survive. At the same time, nature reflects those, which are poorly developed. Hence natural selection
is weeding out the process by which only the fittest individual is selected.
ORIGIN OF NEW SPECIES: As the favourable variations of the fittest animals are inherited to the
offsprings, these variations accumulated over the generations. After several generations, the
organisms become so different from the original species that they lead to the origin of new species.
4. EXAMPLES TO SUPPORT THEORY OF NATURAL
SELECTION
The case of the peppered moth in England is the most frequently discussed example of natural selection.
This refers to an increase in the number of dark coloured moths due to increased industrial pollution. This is
also referred as industrial melanism.
Before the industrial revolution, dark coloured moths were hardly known. The light coloured species
were adapted to rest during the day on lichen coloured trunks of trees.
But due to increase in sulphur dioxide in air because of the industries, the lichens started to reduce on
tree trunks, exposing darker bark which was further darkened by falling smoke particles.
Now the light coloured species become conspicuous and attracted its predators.
For the survival of moths, nature produced a mutation leading to dark coloured moth species from light
coloured species.
Within a period of few years, the industrial or polluted areas saw that the dark species had almost
replaced the light species. Through this, moth showed natural selection at work.
MODERN THEORY OF EVOLUTION
NEO DARWINISM
It is the most accepted theory of evolution now. According to this theory called neo Darwinism, the origin of
species is based on :
1. The interaction of genetic variation.
2. Natural selection.
It incorporates the knowledge of genetics with the basic structure of Darwin’s theory.
This theory takes into account evidences from genetic, molecular biology, fossils, ecology etc.
It takes into account the charges that may arise due to the accumulation of mutations in a population.