The Origin of Life and Evidences of Evolution:
1. The study of history of life forms on earth is called evolutionary biology.
2. Evolution is a process that results in heritable changes in population spread over many generations leading to diversity of organisms on earth.
3. Origin of life is considered a unique event in the history of universe.
(i) The Universe
(a) It is very old-almost 20 billion years ago. It contains huge galaxies.
(b) Galaxies contain stars and clouds of gas and dust.
(c) The origin of universe is explained by Big Bang theory.
(d) The Big Bang theory states that a huge explosion occurred, the universe expanded, temperature came down and hydrogen and helium were formed later. The galaxies were then formed due to condensation of gases under gravitation.
(ii) The earth was supposed to have been formed about 4.5 billion years back in the solar system of the milkyway galaxy.
(a) Water vapour, methane, carbon dioxide and ammonia released from molten masses covered the surface.
(b) UV rays from the sun broke up water molecule into hydrogen and oxygen and lighter hydrogen escaped.
(c) Oxygen combined with ammonia and methane to form water, carbon dioxide and others.
(d) Ozone layer formed, as it cooled, the water vapour fell as rain to fill depression and form oceans.
(e) Life appeared 500 million (about 4 billion years back) years after the formation of earth.
4. Theories of origin of lifewere given by different thinkers and scientists.
(i) Theory of special creation states that God created life by his divine act of creation.
(iii) Theory of panspermia/cosmozoic theory, given by early Greek thinkers states that the spores or panspermia came from outer space and developed into living forms.
(iii) Theory of spontaneous generation states that life originated from decaying and rotting matter like straw, mud, etc.
(a) Louis Pasteur rejected the theory of spontaneous generation and demonstrated that life came from pre-existing life.
(b) In his experiment, he kept killed yeast cells in pre-sterilised flask and another flask open into air. The life did not evolved in the former but new living organisms evolved in the second flask.
(iv) Theory of chemical evolution or Oparin-Haldane theory states that life originated from pre-existing non-living organic molecules and that formation of life was preceded by chemical evolution.
The conditions on the earth that favoured chemical evolution were very high temperature, volcanic storms and reducing atmosphere that contained CH4,NH3, water vapour, etc.
5. Miller’s experimentprovided experimental evidence for chemical evolution.
(i) The experiment was carried out by SL Miller and HC Urey in 1953.
(ii) He took a closed flask containing CH4,H2,NH3 and water vapour at 800°C and created electric discharge. These conditions were similar to those in primitive atmosphere.
(iii) After a week, formation of amino acids were observed. Complex molecules like sugars, nitrogen bases, pigments and fats were seen in the flask by other scientist.
(iv) Analysis of the meteorite also revealed the presence of similar compounds.
(v) Chemical evolution of life was more or less accepted.

6. Origin of First Cell
(i) First non-cellular life forms originated three million years ago.
(ii) These molecules were like RNA, protein and polysaccharides.
(iii) Cellular life form first evolved about 2000 million years ago.
(iv) These were single-celled formed in aquatic environment.
(v) This form of abiogenesis, i.e. the first form of life arose slowly through evolutionary
forces from non-living molecules It is accepted by many scientists.

Evolution of life forms – A theroy.

Conventional religious literature tells us about the theory of special creation.

 The theory of special creation has three connotations:-

o All the living organisms (species types) that we see today were created as

such.

o The diversity was always the same since creation and will be same in

future.

o Earth is about 4000 years old.

Challenge to special creation theory:

 Observation made during a sea voyage in a sail ship called H.M.S. Beagle round

the world. Charles Darwin concluded that existing life forms share similarities to

varying degrees not only among themselves but also with life forms that millions

of years ago.

 Many such life forms exist anymore. There had been extinctions of different life

forms in the years gone by just as new forms of life arose at different periods of

history of earth.

 There has been gradual evolution of life forms.

 Any population has built in variation in characteristics.

 Those characteristics which enable some to survive better in natural conditions

(climate, food, physical factors etc.) would outbreed others that are less-endowed

to survive under such natural condition.

 Survival of the fittest. The fitness according to Darwin refers ultimately and only

leaves more progeny than others.

 These, therefore, will survive more and hence are selected by nature. He called it

as natural selection.

 Alfred Wallace, a naturalist who worked in Malay Archipelago had also come

to similar conclusions around the same time.

 The geological history of earth closely correlates with the biological history of

earth.
7. Evidences of evolution come from(i) Palaeontology (ii) Comparative anatomy and morphology(iii) Biochemical/Physiology (iv) Biogeography(v) Embryology
(i) Palaeontology is the study of fossils. The fossils are the remains of past organisms
preserved in sedimentary rocks
(a) Rocks form sediments and a cross-section of earth’s crust indicates the arrangement of sediments one over the other during the long history of earth.
(b) Different aged rock sediments contain fossils of different life forms, who died during the formation of the particular sediment,
(c) Some organisms appear similar to modern organisms. They represent extinct organisms like dinosaurs.
(d) A study of fossils in different sedimentary layers indicates the geological period in which they existed.
(e) The study showed that life forms varied over time and certain life forms are restricted to certain geological time-scale Hence, new forms of life have evolved at different times in the history of earth,
(ii) Comparative anatomy and morphological evidences show the similarities and
differences among the organisms of today and those that existed years ago.
The evidences come from comparative study of external and internal structure.
I. (a) The organs with same structural design and origin but different functions are called homologous organs. Examples are forelimbs of some animals like whales, bats and cheetah have similar anatomical structure, such as humerus, radius, ulna, carpals, metacarpals and phalanges.
(b) Homology in organ indicates common ancestry.
(c) Other examples of homology are vertebrate hearts or brains. In plants also, thorns and tendrils of Bougainvillea and Cucurbita represent homology.
(d) Homology is based on divergent evolution. The same structure developed along different directions due to adaptations to different needs. The condition is called divergent evolution.

II. (a) Organs which are anatomically different but functionally similar are called analogous organs. For example, wings of butterfly and birds.
(b) Analogy refers to a situation exactly opposite to homology.
(c) Analogous organs are a result of convergent evolution. It is the evolution in which different structures evolve for same function and hence, have similarity.
(d) Other examples of analogy are eyes of Octopus and mammals; flippers of penguins and dolphins. In plants, sweet potato (root modification) and potato (stem modification).

III. Vestigial organslike homologous organs provide evidences for organic evolution.
These are degenerate, non-functional and rudimentary organs to the possessor, while correspond to fully developed and functional organs of related organisms.
(a) There are about 90 vestigial organs in the human body. Same of them are tail bone (coccyx), wisdom teeth, nictitating membrane, vermiform appendix, etc.
(b) Some examples from other animals are hip girdles and bones of the hind limbs in some whales and certain snakes and wings of flightless birds.
Biochemical Evidences
(a) The metabolic processes in organisms are similar with same new materials and end products. For example, energy released by oxidation is stored in ATP which then powers the energy requiring process.
(b) Molecular homology is the similarity among animals at the molecular level.
For example, human DNA differs in only 1.8% of its base pairs from chimpanzee DNA and there is no difference between the two in the amino acid sequence for the protein cytochrome-c.
(iv) Biogeographical evidences The species restricted to a region develop unique features. Also, species present in far separated regions show similarity of ancestry.
This can be explained with the help of following processes:
I. Adaptive radiation is an evolutionary process in which an ancestral stock gives rise to new species adapted to new habitats and new ways of life. Examples are (0 Darwin’s finches These were small black birds, which Darwin observed in Galapagos island.
(a) He observed many varieties of finches in the same island.
(b) All varieties of finches had evolved from original seed-eating finches.
(c) There was alternation in beaks enabling some to become insectivorous and some vegetarian.

(ii) Marsupials of Australia A number of marsupials, different from each other evolved from an ancestral stock, all within the Australian island continent.
II. Parallel evolution refers to independent development of similar characters in two animal groups of common ancestry living in similar habitats of different continents. Examples are
Marsupial mammals in Australia show parallel evolution as they have evolved from placental mammals. All these closely resemble and look similar to a corresponding marsupial.
Few examples are mentioned in the table.

III. Convergent evolution is development of similar adaptive functional structures in unrelated groups of organisms. Examples are:
(i) Wings of insect, bird and bat.
(ii) Spiny anteater and scaly anteater belong to different orders of class-Mammalia. They have acquired similar adaptations for food, e.g. leg ants, termites and insects.
(v) Embryological evidences Study of comparative embryology shows common patterns of development.
(a) The principles of embryonic development were given by Von Baer.
(b) Ernst Haeckel propounded The theory of recapitulation or Biogenetic law which states that an individual organism in its development (ontogeny) tends to repeat the stages passed through by its ancestors (phylogeny), i.e. ontogeny recapitulates phylogeny.
(c) This means that the life history of an animal reflects its evolutionary history.
For example, during the life history, frog’s tadpole larva resembles fishes, the ancestors of amphibia.
The presence of gill clefts in all vertebrate embryos including human provides a strong evidence in support of organic evolution.
(vi) Anthropogenic evidences Excess use of herbicides, pesticides, etc has resulted in selection of resistant varieties in a lesser time scale. This is also true for microbes against which antibiotics or drugs have been used. All these evidences tell us that ‘Evolution is a stochastic process based on chance events in nature and chance mutation in the organisms’.

WHAT IS ADAPTIVE RADIATION?

Darwin’s Finches:

 In Galapagos Islands Darwin observed small black birds later called Darwin’s

Finches.

 He realized that there were many varieties of finches in the same island.

 All the varieties, he came across, evolved on the island itself.

 Form the original seed-eating features, many other forms with altered beaks

arose, enabling them to become insectivorous and vegetarian finches

 This process of evolution of different species in a given geographical area starting

from a point and literally radiating to other areas of geography (habitats) is called

adaptive radiation.

Australian marsupial:

 A number of marsupials each different from the other evolved from an ancestral

stock. But all within the Australian island continent.

 When more than one adaptive radiation appeared to have occurred in an isolated

geographical area (representing different habitats), one can call this convergent

evolution.

 Placental mammals in Australia also exhibit adaptive radiation in evolving into

varieties of such placental mammals each of which appears to be ‘similar’ to a

corresponding marsupial (e.g.- placental wolf and Tasmanian wolf-marsupial).

BIOLOGICAL EVOLUTION:

 The essence of Darwinian Theory about evolution is natural selection.

 The rate of appearance of new forms is linked to the life cycle or the life span.

 There must be a genetic basis for getting selected and to evolve.

 Some organisms are better adapted to survive in an otherwise hostile

environment.

 Adaptive ability is inherited.

 It has genetic basis.

 Fitness is the end result of the ability to adapt and get selected by nature.

 Branching descent and natural selection are the two key concepts of Darwinian

Theory of Evolution.

Lamarck theory of evolution (theory of inheritance of acquired characters):

 French Naturalist Lamarck had said that evolution of life forms had occurred but

driven by use and disuse of organs.

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 He gave the example of Giraffes who in an attempt to forage leaves on tall trees

had to adapt by elongation of their necks.

 They passed on this acquired character of elongated neck to succeeding

generations.

 Giraffes, slowly over the years, came to acquire long necks.

MECHANISM OF EVOLUTION:

 In the first decade of twentieth century, Hugo de Vries based on his work on

evening primrose brought forth the idea of mutations.

 Mutation is the large difference arising suddenly in a population.

How de Vries theory of mutation differs from Darwin’s theory of natural selection?

 It is the mutation which causes evolution and not the minor variations that Darwin

talked about.

 Mutations are random and directionless while Darwinian variations are small and

directional.

 Evolution for Darwin was gradual while de Vries believed mutation caused

speciation and hence called it saltation (single step large mutation).

The Hardy-Weinberg principle is an important concept in biology, particularly in the study of evolution. It helps us understand how genetic traits in a population can remain stable from generation to generation if certain conditions are met. Let’s break it down into easy-to-understand language.

The Hardy-Weinberg principle states that in a large, randomly mating population, the frequencies of different genetic traits will remain constant over time if no other factors are at play. This means that the proportion of individuals with a specific trait, such as eye color or blood type, will stay the same from one generation to the next.

Now, let’s talk about the mathematical explanation of the Hardy-Weinberg principle. It involves some simple equations, but don’t worry, we’ll keep it easy. There are two main equations involved:

p^2 + 2pq + q^2 = 1: This equation represents the distribution of genetic traits in a population. Let’s break it down:

p^2 represents the frequency of individuals with a homozygous dominant genotype (having two copies of the dominant allele).

2pq represents the frequency of individuals with a heterozygous genotype (having one copy of the dominant allele and one copy of the recessive allele).

q^2 represents the frequency of individuals with a homozygous recessive genotype (having two copies of the recessive allele).

The sum of these frequencies (p^2 + 2pq + q^2) equals 1, which means it accounts for all the individuals in the population.

p + q = 1: This equation simply states that the frequencies of the two alleles (dominant and recessive) in a population should add up to 1. Here, p represents the frequency of the dominant allele, and q represents the frequency of the recessive allele.

The Hardy-Weinberg principle describes the conditions under which the genetic composition of a population remains stable over generations. Deviations from this principle can occur due to various factors. Here are five factors known to affect the Hardy-Weinberg principle:

Mutation: Mutations introduce new genetic variations into a population. If a mutation occurs in a gene that affects the trait under consideration and provides a selective advantage or disadvantage, it can disrupt the equilibrium predicted by the Hardy-Weinberg principle.

Genetic Drift: Genetic drift refers to the random fluctuation of allele frequencies in a population due to chance events. In small populations, genetic drift can have a significant impact on allele frequencies and lead to deviations from the Hardy-Weinberg equilibrium.

Migration (Gene Flow): Migration, or the movement of individuals between populations, can introduce new alleles into a population or remove existing ones. If migration is significant, it can disrupt the equilibrium predicted by the Hardy-Weinberg principle.

Gentic Recombination(Non-Random Mating): The Hardy-Weinberg principle assumes random mating, where individuals have an equal chance of mating with any other individual in the population. Non-random mating, such as assortative mating (mating with individuals who have similar traits) or inbreeding (mating between close relatives), can lead to deviations from the expected equilibrium.

Natural Selection: Natural selection acts on the genetic variation in a population, favoring certain traits that increase an organism’s fitness. If a particular genotype provides a selective advantage or disadvantage, it can change the allele frequencies and lead to deviations from the Hardy-Weinberg equilibrium.

It’s important to note that these factors can individually or collectively influence the genetic composition of a population and cause deviations from the Hardy-Weinberg equilibrium.

Now, let’s talk about the founder effect. The founder effect is a phenomenon that occurs when a small group of individuals establishes a new population in a different area, thereby carrying only a fraction of the original population’s genetic diversity. Due to the limited number of individuals, the new population may have a different genetic makeup compared to the original population.

To explain it simply, imagine a small group of people moving to a new island. Let’s say this group has a higher proportion of individuals with blond hair compared to the general population. Over time, the new population on the island may have a higher frequency of blond hair due to the founder effect.

In summary, the Hardy-Weinberg principle helps us understand how genetic traits can remain stable in a population, assuming certain conditions are met. The mathematical equations associated with the principle describe the frequencies of different genetic traits. The founder effect, on the other hand, refers to the change in genetic diversity that can occur when a small group establishes a new population.

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explanation of page 137 para 3 , also use fig 7.8 to explain this

Microbial experiments have shown that when certain beneficial mutations are selected, new observable traits can emerge. This process can lead to speciation, which means the formation of new species.

Natural selection is a process where certain traits that help organisms survive and reproduce better are passed on to future generations. These traits can come from different sources like mutations (random changes in genetic material), recombination during the formation of reproductive cells, gene flow (movement of genes between populations), or genetic drift (random changes in gene frequencies).

As these traits become more common in a population over time, it can make the population look different from other populations. This is because natural selection can cause three main types of changes: stabilization, directional change, or disruption.

Stabilization occurs when more individuals in a population acquire the average or typical value for a particular trait. For example, if the average height of a population of plants is 50 cm, natural selection may favor individuals that are closer to this average, resulting in more plants being around this height.

Directional change happens when more individuals acquire a trait value that is different from the average. Let’s say there’s a population of birds with different beak sizes, and there’s a sudden increase in the availability of large seeds. Natural selection may favor birds with larger beaks, leading to more individuals in the population having larger beak sizes over time.

Disruption occurs when more individuals in a population acquire extreme values for a trait, while fewer individuals have intermediate values. Imagine a population of butterflies with different wing colors, where the environment becomes divided into two habitats with different light conditions. Natural selection may favor butterflies with very light or very dark wings in each habitat, resulting in fewer individuals having intermediate wing colors.

In summary, natural selection can cause changes in populations over time by favoring certain traits that help with survival and reproduction. These changes can lead to populations looking different from one another, either by stabilizing around an average trait value, shifting towards a different value, or developing extreme values at both ends of the spectrum.

A brief account of Evolution

Certainly! Here’s a simplified explanation of the evolution of life forms on Earth along with a flowchart:

Around 2000 million years ago, the first cellular forms of life appeared on Earth. These were simple cells that had the ability to release oxygen (O2).

The process of how non-cellular aggregates of giant macromolecules evolved into cells with membranous envelopes is still unknown.

Over time, single-celled organisms began to evolve into multi-cellular life forms.

Around 500 million years ago, invertebrates (animals without backbones) started to appear and become active.

Jawless fish likely evolved around 350 million years ago.

Sea weeds and a few plants existed around 320 million years ago.

The first organisms to invade land were plants. They were already widespread on land when animals followed suit.

Around 350 million years ago, fish with stout and strong fins were able to move on land and return to water.

In 1938, a fish called the Coelacanth, which was thought to be extinct, was discovered in South Africa. These lobefin fish evolved into the first amphibians that could live on both land and water. They were ancestors of modern-day frogs and salamanders.

Amphibians eventually evolved into reptiles. Unlike amphibians, reptiles laid thick-shelled eggs that didn’t dry up in the sun.

Reptiles of various shapes and sizes dominated the Earth for the next 200 million years or so. Giant ferns (pteridophytes) were present during this time but eventually formed coal deposits.

Some land reptiles returned to the water and evolved into fish-like reptiles around 200 million years ago (e.g., Ichthyosaurs). The land reptiles were known as dinosaurs, with the largest of them being Tyrannosaurus rex.

Approximately 65 million years ago, dinosaurs suddenly disappeared from the Earth. The exact reason for their extinction is unknown, but some theories suggest climatic changes or evolution into birds.

The first mammals were small-sized and resembled shrews. They were viviparous, meaning they gave birth to live young and protected them inside the mother’s body.

When the dinosaurs became extinct, mammals began to dominate the Earth. In South America, there were mammals resembling horses, hippos, bears, rabbits, and more. However, when South America joined North America due to continental drift, these animals were overtaken by North American fauna.

Pouched mammals in Australia survived and thrived due to a lack of competition from other mammals, thanks to the continent’s isolation.

Some mammals adapted to live wholly in water, such as whales, dolphins, seals, and sea cows.

The evolution of specific animals like horses, elephants, and dogs is a more detailed story that you will learn about in higher classes.

The most remarkable success story of evolution is the evolution of humans, who possess language skills and self-consciousness.

Flowchart:

[First cellular forms of life appeared] -> [Evolution of single-celled to multi-cellular organisms] -> [Invertebrates appear] -> [Jawless fish evolve] -> [Sea weeds and few plants exist] -> [Plants invade land] -> [Fish with stout fins move on land] -> [Lobefin fish evolve into amphibians] -> [Amphibians evolve into reptiles] -> [Reptiles dominate, including dinosaurs] -> [Dinosaurs become extinct] -> [Small-sized mammals appear] -> [Mammals dominate, with South American fauna overtaken] -> [Pouched mammals survive in Australia] -> [Marine mammals evolve] -> [Evolution of specific animals] -> [Evolution of humans with language skills and self-consciousness]

Origin and Evolution of Humans:

Around 15 million years ago (mya), primates called Dryopithecus and Ramapithecus existed. They were hairy and walked like gorillas and chimpanzees. Ramapithecus had more human-like features, while Dryopithecus was more ape-like.

Fossils of man-like bones discovered in Ethiopia and Tanzania revealed hominid features, suggesting that about 3-4 mya, man-like primates walked in eastern Africa. They were probably not taller than 4 feet but walked upright.

Approximately 2 mya, Australopithecines likely lived in East African grasslands. They showed evidence of hunting with stone weapons but mainly ate fruit. Among the discovered bones, a creature called Homo habilis was identified as the first human-like being. Homo habilis had a brain capacity between 650-800cc and probably did not eat meat.

Fossils found in Java in 1891 revealed the next stage, Homo erectus, which emerged around 1.5 mya. Homo erectus had a larger brain, approximately 900cc, and is believed to have consumed meat.

Neanderthal man, with a brain size of 1400cc, lived in the Near East and central Asia between 100,000 and 40,000 years ago. They used hides for protection and buried their dead.

Homo sapiens, our species, originated in Africa and gradually migrated across continents, giving rise to distinct races. During the ice age, between 75,000 and 10,000 years ago, modern Homo sapiens emerged.

Around 18,000 years ago, prehistoric cave art began to develop.

Agriculture emerged approximately 10,000 years ago, leading to the establishment of human settlements.

The subsequent events are part of human history, including the growth and decline of civilizations.

Flowchart:

15 mya: Dryopithecus and Ramapithecus existed.

Dryopithecus: Ape-like features

Ramapithecus: More man-like features

3-4 mya: Man-like primates in eastern Africa.

Walked upright, not taller than 4 feet

2 mya: Australopithecines in East African grasslands.

Stone weapon use for hunting

Ate mainly fruit

Homo habilis: First human-like being, brain capacity of 650-800cc

1.5 mya: Homo erectus discovered in Java.

Larger brain size (approximately 900cc)

Meat consumption

100,000-40,000 years ago: Neanderthal man.

Brain size of 1400cc

Use of hides for protection

Burial of the dead

Homo sapiens:

Originated in Africa

Migrated across continents

Different races developed

Ice Age (75,000-10,000 years ago): Modern Homo sapiens emerged.

18,000 years ago: Prehistoric cave art developed.

10,000 years ago: Agriculture began, leading to human settlements.

Subsequent events are part of human history, including the growth and decline of civilizations.