REVISION NOTES                               

Evolutionary Biology is the study of history of life forms on the earth. To understand the changes in flora and fauna that have occurred millions of years on earth we must have a strong understanding of the context of life, that is evolution of earth, the stars, and the universe itself.

Origin of Life

The genesis of life is regarded as a one-of-a-kind occurrence in the history of the cosmos. The universe is made up of a massive cluster of galaxies. Galaxies include stars as well as dust and smoke clouds. 
The Big Bang Theory seeks to explain the origins of the cosmos. According to this idea, a massive explosion occurs, resulting in the formation of many galaxies.
 Earth is thought to have originated some 4.5 billion years ago in the Milky Way galaxy's solar system. The early Earth had no atmosphere. The earth's surface was coated with water vapour, methane, carbon dioxide, and ammonia emitted by the molten mass.
 The sun's UV rays split water into hydrogen and oxygen. Life arose 500 million years after the Earth's formation.

Theories in support of Origin of Life 
• Greek thinkers believed that spores brought from other planets were the basic unit of life.
 • According to another hypothesis, life emerges from dead and decaying substances such as straw and dirt. This is known as the hypothesis of spontaneous origin. 
Louis Pasture demonstrated experimentally that life can only come from pre-existing life. Following that, the spontaneous theory of the origin of life is discarded. 
Oparin and Haldane argued that the initial form of life may have evolved from non-living organic molecules such as RNA and protein. Chemical evolution precedes the origin of life. At that period, the earth's conditions were as follows:
 (i) high temperatures
 (ii) volcanic eruptions, and 
(iii) reducing atmosphere that comprised of CH4 and NH3.

 Miller’s Experiment: In 1953, S.L. Miller undertook an experiment to demonstrate the origin of life on Earth in a physical environment comparable to that which existed at the time. Miller created identical temperature and pressure conditions in the laboratory. At 8,000 degrees Celsius, he established an electric discharge in a flask containing CH4, H2, NH3, and water vapour. After 15 days of electric discharge, he saw the synthesis of amino acids in a flask. Another scientist discovered the creation of sugars, nitrogen bases, colours, and lipids in a similar procedure. Analysis of meteorite material revealed comparable molecules, indicating that similar processes are taking place elsewhere in space. This experimental evidence for the genesis of life is referred to as the chemical evolution of life. The first non-cellular forms of life may have evolved three billion years ago. They might have been massive molecules like RNA, Protein, and Polysaccharide, among others. The cellular form of life most likely began as a single cell in an aqueous medium. Biogenesis is the hypothesis that the initial form of life evolved slowly through evolutionary processes from non-living components. 

Evidence of evolution:

some of the evidence of the evolution of life forms are as follows: 
(i) Paleontological evidence: Various ages of rock sediments include remains of various living forms that most likely died during the sediment's development. Fossils are the hard remnants of life-forms discovered in rocks. The study found that diverse forms changed through time and that particular living forms had a geological time span. As a result, new types of life have emerged at various points throughout Earth's history. 
(ii) Homologous organs: Homologous organs are ones that perform distinct functions but have a similar origin and structure. Humans, cheetahs, bats, and whales, for example, show similarities in the arrangement of bones in their forelimbs, despite the fact that these forelimbs serve different tasks in these creatures. Because of adaptation to distinct demands, these animals evolved identical structures in opposite orientations. This is referred to as divergent evolution.
(iii) Analogous structures: They are not morphologically identical organs, yet they serve the same purpose. For example, the eyes of mammals and octopuses, as well as the flippers of penguins and dolphins. This is because distinct groups of species have comparable adaptation traits owing to similar environment. This process of evolution is known as convergent evolution. 
(iv) Biochemical evidence: Similarities in proteins and genes that execute the same function in different species suggest a common ancestor. These molecular similarities, like structural similarities, indicate common ancestor.

Evolution by Natural Selection

 Industrial Melanism: Natural selection was seen in a peppered moth in England in the 1850s, prior to industrialization (Biston betularia). 
• This moth came in two colours: grey and black (Carbonaria). Before industrialisation in the early nineteenth century, only the grey-colored moths were present; the black ones were uncommon. 
• The grey-colored moths were found on tree trunks coated in lichens, allowing them to flee their assailants. 
• Later, around 1920, when industries developed, postindustrialization, the lichens died and the tree trunks became black owing to the deposition of industrial soot. Birds may now locate these moths and feast on them.
 • As a result, the grey-colored moths were devoured by the birds, but the dark-colored moths fled. 
• The coal is currently being replaced by industries, which utilise oil and electricity. This has resulted in less soot generation and, as a result, decreased soot deposition on tree trunks. 
• These tree trunks have now become grey once more. As a result, the number of grey-colored moths has grown once more. 
              (a) unpolluted area    (b) polluted area

Evolution by Anthropogenic Selection: e.g. resistance of mosquitoes to pesticides.
DDT was a huge success when it was used to control mosquitoes. The majority of the mosquitos were DDT sensitive and were so eliminated. Few mosquitos in that population acquired resistant to DDT and survived. They grew and now the entire mosquito population developed resistance to DDT. The same pattern has been found in bacteria that are multidrug resistant as a result of excessive medication and pharmaceutical usage. 

Adaptive Radiation

it refers to the process of evolution of diverse species in a specific geographical region that begins at a point and spreads to other parts of geography (habitat). Darwin's finches are an excellent illustration of adaptive radiation. Australian marsupials developed from a common ancestor stock, yet all lived on Australian island continents.

Convergent evolution occurs when more than one adaptive radiation appears to have occurred in a geographically separated location (representing distinct ecosystems), for example, Placental mammals and Australian marsupials. 

Biological Evolution:

Nature favours the fittest, and fitness is determined by hereditary qualities. Some species have evolved to thrive in hazardous environments. Fitness is the final outcome of one's capacity to adapt to and be chosen by nature. 
According to Lamarck, evolution of living forms happened but was driven by the use and misuse of organs. He used giraffes as an illustration of how they evolved their necks by harvesting leaves on lofty trees and had to adjust by elongating their necks. 
The two essential principles of Darwinian Theory of Evolution are: 
(i) branching descent and 
(ii) natural selection.  
Darwin's theory of natural selection was based on following observation: 
• Natural resources are scarce. 
• Population growth 
• Competition for scarce resources 
• Survival for existence. 
• Survival of the fittest 
Mechanisms of Evolution: 
Hugo deVries proposed the concept of mutation based on his research on evening primrose (Oenothera lamarckiana). 
• A mutation is a substantial change that appears abruptly in a population. 
• Darwin variations are modest and directed, whereas mutations are random and directionless. 
• Hugo deVries thought that mutation produced speciation, which he referred to as saltation (single step large mutation).

Hardy-Weinberg Principle 

The frequency of occurrence of alleles or genes in a given population can be determined. These frequencies remain constant and even during generation. Hardy-Weinberg concepts were used to describe this information using an algebraic equation. According to this theory, allele frequencies in a population remain steady and consistent from generation to generation. The gene pool does not change. This is known as genetic equilibrium, and the sum of all allelic frequencies equals 1. 
Binomial expansion of (p + q)2= p2+2pq+q2=1 where p and q are the frequencies of allele A and a in a population.
The frequency of AA people in a population is simply p2. 
Just put, the likelihood of an allele A with a frequency of p appearing on both chromosomes of a diploid person is simply the product of the probabilities, i.e., p2. Similarly, aa is q2, and Aa 2pq. As a result, p2 + 2pq + q2 = 1. 
When measuring frequency, the actual value varies, indicating the level of evolutionary changes.
 Change of frequency in alleles (Hardy-Weinberg equilibrium) in a population resulted due to evolution.

 Factors Affecting Hardy-Weinberg principle are: 

(i) Gene migration/gene flow
 (ii) Genetic drift 
(iii) Mutation 
(iv) Genetic recombination 
(v) Natural selection During genetic drift, changes in allele frequency might be so diverse in a population sample that they form a separate species. The original drifted population becomes founder and that effect is called founder effect.

Brief Account of Evolution 

• The earliest cellular form of life evolved on Earth some 2000 million years ago.
 • Slowly, single-celled animals evolved into multicellular forms, and by 500 million years ago, invertebrates were developed and active. 
• Around 350 million years ago (mya), jawless fish originated. 
• Organisms began to spread from the sea to the land. Fish with large and powerful fins may travel on land and return to the water. These lobefin creatures developed into the earliest amphibians.
 • These amphibians later evolved into reptiles. They produce shelled eggs. The planet was once dominated by reptiles of all forms and sizes, including fish-like reptiles such as Ichthyosaurs and terrestrial reptiles such as dinosaurs. Tyrannosaurus rex was the largest. 
• Some of the reptiles developed into birds, while others into mammals. Mammals were viviparous and better at perceiving and avoiding danger.

Origin and Evolution of Man

 Dryopithecus: evolved in 15 mya. They were hairy and walked like gorillas and chimpanzees. They were more apelike.
 Ramapithecus: they were more man like. 
Australopithecus: they lived in East African grasslands. Discovered 2 mya. They hunted with stone weapons and ate fruits. Homo habilis: this was first human like. Its brain capacity was 650-800cc. They did not eat meat. 
Homo erectus: discovered 1.5 mya. They had a large brain with a brain capacity of 900cc. They ate meat. 
Neanderthal man: it had a brain capacity of 1400cc and lived near east and central Asia. They used hides to protect their body and were the first to bury their dead. 
Homo sapiens: they arose in Africa and moved to other continents and developed into different races. 

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