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• The universe is vast, with stars appearing millions of years ago and galaxies containing stars and clouds of gas and dust. • The Big Bang theory suggests a singular, massive explosion that expanded the universe, causing a drop in temperature and the formation of hydrogen and helium. Earth Formation • Earth was believed to have been formed about 4.5 billion years ago in the Milky Way galaxy. • The formation of earth was influenced by water vapor, methane, carbon dioxide, and ammonia released from molten mass. • Life appeared 500 million years after the formation of earth, almost four billion years ago.
Theory of Spontaneous Generation • Some scientists believe life came from outerspace, with early Greek thinkers suggesting spores were transferred to different planets, and 'Panspermia'. • Louis Pasteur demonstrated that life comes only from pre-existing life, dismissing the spontaneous generation theory. The First Life Form on Earth • Operin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing non-living organic molecules. • The formation of life was preceded by chemical evolution, i.e., the formation of diverse organic molecules from inorganic constituents.
The First Self-Replicating Metabolic Capsule of Life • The first non-cellular forms of life could have originated 3 billion years ago, possibly being giant molecules. • The first cellular form of life did not possibly originate till about 2000 million years ago, likely single-cells. • The evolution of the first cellular forms of life into the complex biodiversity of today remains a fascinating story.
• The theory of special creation suggests all living organisms were created. • Darwin's observations during a voyage in the H.M.S. Beagle challenged these ideas. • Darwin concluded that existing living forms share similarities with life forms that existed millions of years ago. • Darwin proposed that life forms have evolved gradually, with some surviving better in natural conditions. • He termed this fitness as reproductive fitness, with those who survive more outbreed others. • Alfred Wallace, a naturalist in the Malay Archipelago, also agreed with Darwin's conclusions.
• Darwin's theory suggests that all life forms share common ancestors, present at different periods in earth's history. • The geological history of earth closely correlates with its biological history, suggesting that earth is billions of years old.
• Fossils are remains of hard parts of life-forms found in rocks. • Different-aged rock sediments contain fossils of different life-forms who died during the formation of the particular sediment. • Some fossils appear similar to modern organisms, representing extinct organisms. Paleontological Evidence • Fossils in different sedimentary layers indicate the geological period in which they existed. • Life-forms varied over time and certain life forms are restricted to certain geological time-spans. • New forms of life have arisen at different times in the history of earth.
Embryological Support for Evolution • Ernst Heckel proposed embryological support for evolution based on the observation of certain features during embryonic stage common to all vertebrates that are absent in adult. • This proposal was disapproved by Karl Ernst von Baer, who noted that embryos never pass through the adult stages of other animals. Comparative Anatomy and Morphology • Comparative anatomy and morphology show similarities and differences among organisms of today and those that existed years ago.
• Similarities in the pattern of bones of forelimbs in whales, bats, Cheetah, and human (all mammals) can be interpreted to understand whether common ancestors were shared or not. • Homology indicates common ancestry, while analogy refers to a situation exactly opposite. Human-Induced Breeding • Man has bred selected plants and animals for agriculture, horticulture, sport, or security, creating breeds that differ from other breeds but still belong to the same group. • An observation from England supports evolution by natural selection, with more white-winged moths on trees than dark-winged or melanised moths in the same area after industrialization.
• Excess use of herbicides, pesticides, etc. has resulted in the selection of resistant varieties in a much lesser time scale.
• Darwin observed a diverse range of creatures, including Darwin's Finches. • He believed that all finches evolved on the island itself, from seed-eating features to insectivorous and vegetarian forms. • This process, known as adaptive radiation, extends to other areas of geography. • Darwin's finches are a prime example of this phenomenon. • Australian marsupials also exhibit adaptive radiation, with different species evolving from an ancestral stock within the Australian island continent. • Convergent evolution occurs when more than one adaptive radiation occurs in an isolated geographical area.
• Placental mammals in Australia also exhibit adaptive radiation, evolving into corresponding marsupial-like varieties.
• Darwinian theory of evolution posits that cellular forms of life with differences in metabolic capability originated on Earth. • The rate of new forms' appearance is linked to the life cycle or life span. • Fast-diving microbes can multiply and become millions of individuals within hours. • A change in the medium composition would bring out only a part of the population that can survive under new conditions. • This population outgrows others and appears as new species. • Fitness is based on inherited characteristics, suggesting a genetic basis for selection and evolution. • Adaptive ability is inherited and has a genetic basis.
• Darwin's theory of evolution and natural selection are key concepts. • Lamarck's conjecture that evolution occurred driven by the use and disuse of organisms is no longer believed. • The distinction between evolution as a process or the result of a process remains unclear. • Darwin's theory suggests that variations that are heritable and make resource utilization better for few enable only those to reproduce and leave more progeny.
• Darwin ignored Mendel's concept of inheritable factors influencing phenotype. • Hugo deVries introduced the idea of mutations in the early 20th century, arguing mutation causes evolution. • DeVries viewed mutations as random, directionless, while Darwinian variations were small, directional. • DeVries termed speciation as saltation, a single step large mutation. 6.7 HARDY-WEINBERG PRINCIPLE
• Hardy-Weinberg principle states that allele frequencies in a population remain stable and constant from generation to generation. • This principle is referred to as genetic equilibrium. • The sum total of all allelic frequencies is represented by p, q, etc. • When frequency measured differs from expected values, it indicates the extent of evolutionary change. • Five factors affect Hardy-Weinberg equilibrium: gene migration, genetic drift, mutation, genetic recombination, and natural selection. • Gene migration involves adding new genes/alleles to the new population, while genetic drift occurs when the same change occurs by chance.
• Mutations or recombination during gametogenesis can result in the same change in allele frequency in future generations. • • Natural selection, a process enabling better survival, can lead to stabilization, directional change, or disruption.
• The first cellular forms of life appeared around 2000 million years ago. • The mechanism of how non-cellular aggregates of giant macromolecules evolved into cells with membranous envelop is unknown. • Some cells could release O2, similar to the light reaction in photosynthesis. • Slowly, single-celled organisms evolved into multi-cellular life forms. • By 500 mya, invertebrates were formed and active. • Jawless fish evolved around 350 mya. • Sea weeds and few plants existed around 320 mya. • The first organisms that invaded land were plants. • Fish with stout and strong fins evolved into the first amphibians that lived on both land and water.
• The amphibians evolved into reptiles, laying thick-shelled eggs that do not dry up in sun unlike amphibians. • Reptiles of different shapes and sizes dominated on earth for 200 million years. • The first mammals were like shrews, with small-sized fossils. • Mammals were viviparous and intelligent in sensing and avoiding danger. • Some mammals lived wholly in water, such as whales, dolphins, seals, and sea cows. • The most successful story is the evolution of man with language skills and self-consciousness.
• Dryopithecus and Ramapithecus, primates around 15 mya, were hairy and walked like gorillas and chimpanzees. • Ramapithecus was more man-like, while Dryopithecus was more ape-like. • Fossils from Ethiopia and Tanzania reveal hominid features, suggesting 3-4 mya man-like primates lived in eastern Africa. • Australopithecines, two mya, lived in East African grasslands, hunted with stone weapons, and ate fruit. • Homo habilis, the first human-like hominid, had a brain capacity between 650-800cc and likely ate meat. • Homo erectus, discovered in Java in 1891, had a large brain around 900cc and likely ate meat.
• Neanderthal man with a brain size of 1400cc lived in near east and central Asia between 1,00,000-40,000 years ago. • Homo sapiens arose in Africa and moved across continents, developing into distinct races. • Pre-historic cave art developed about 18,000 years ago, and agriculture emerged around 10,000 years ago.
• Origin of life on earth is based on the universe's origin, particularly Earth. • • Most scientists believe chemical evolution preceded the first cellular forms of life. • • Darwinian ideas of organic evolution by natural selection are used to explain the subsequent events. • • Life form diversity on earth has been changing over millions of years. • • Variations in population result in variable fitness, leading to new species and evolution. • • Homology is accounted for by branching descent. • • Comparative anatomy, fossils, and biochemistry provide evidence for evolution. • • Modern man's evolution parallels human brain and language evolution.
