EVOLUTION
EVOLUTION
1.EVOLUTIONARY BIOLOGY is the study of history of life forms on earth.
2.The universe is almost 20 billion years old.
3.The BIG BANG THEORY attempts to explain to us the origin of universe.
4.In the solar system of the milky way galaxy, earth was supposed to have been formed about 4.5 billion years back.
5.There was no atmosphere on early earth.
6.How the early atmosphere formed?
•Water vapour, methane, carbon dioxide and ammonia released from molten mass covered the surface.
•The UV rays from the sun broke up water into Hydrogen and Oxygen and the lighter H2 escaped.
•Oxygen combined with ammonia and methane to form water, CO2 and others.
•The ozone layer was formed.
•As it cooled, the water vapour fell as rain, to fill all the depressions and form oceans.
7.Life appeared 500 million years after the formation of earth, i.e., almost four billion years back.
8.Louis Pasteur –> Experimently demonstrated that life comes only from pre-existing life.
9.Oparin of Russia and Haldane of England
•Proposed that the first form of life could have come from pre- existing non-living organic molecules (e.g. RNA, protein, etc.)
“CHEMICAL EVOLUTION”
•The conditions on earth were – high temperature, volcanic storms, reducing atmosphere containing CH4, NH3, etc.
•In 1953, S.L. Miller, an American scientist created similar conditions in a laboratory scale.
10.The first non-cellular forms of life could have originated 3 billion years back.
•Giant molecules (RNA, Protein, Polysaccharides, etc.).
•These capsules reproduced their molecules perhaps.
11.The first cellular form of life did not possibly originate till about 2000 million years ago. These were PROBABLY SINGLE-CELLS.
12.All life forms were in water environment only.
13.Biogenesis, i.e., the first form of life arose slowly through evolutionary forces from non-living molecules is accepted by majority.
14.CHARLES DARWIN
•Travelled on sail ship called H.M.S. Beagle
•Concluded that
o existing living forms share similarities to varying degrees not only among themselves but also with life forms that existed millions of years ago.
o Many such life forms do not exist anymore.
o Continuous extinctions of different life forms –> new forms of life arose at different periods of history of earth.
oThere has been gradual evolution of life forms.
oAny population has built in variation in characteristics.
oThose 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 conditions.
oFitness of the individual or population –> according to Darwin, only reproductive fitness.
oHence, those who are better fit in an environment, leave more progeny than others. These, therefore, will survive more and hence are selected by nature.
oHe called it NATURAL SELECTION and IMPLIED IT AS A MECHANISM OF EVOLUTION.
15.ALFRED WALLACE
•A naturalist
•Worked in Malay Archepelago
•Had conclusions similar to Darwin around the same time.
•All the existing life forms share similarities and share common ancestors.
16.THE EVIDENCES FOR EVOLUTION
•FOSSILS
oFossils (remained of hard parts of life-forms found in rocks).
oDifferent-aged rock sediments contain fossils of different life-forms
oA study of fossils in different sedimentary layers indicates the geological period in which they existed.
oThe study showed that life-forms varied over time and certain life forms are restricted to certain geological time-spans. Hence, new forms of life have arisen at different times in the history of earth.
oAll this is called PALEONTOLOGICAL EVIDENCE.
oAge of Fossils Radioactive dating
•
HOMOLOGY
oWhales, bats, Cheetah and human (all mammals) share similarities in the pattern of bones of forelimbs –>Though these forelimbs perform different functions in these animals, they have similar anatomical structure. Hence, in these animals, the same structure developed along different directions due to adaptions to different needs.
oTHIS IS DIVERGENT EVOLUTION AND THESE STRUCTURES ARE HOMOLOGOUS.
oHOMOLOGY INDICATES COMMON ANCESTRY.
o In plants also, the thorn and tendrils of Bougainville a and Cucurbita represent homology.
oHOMOLOGY IS BASED ON DIVERGENT EVOLUTION WHEREAS ANALOGY REFERS TO A SITUATION EXACTLY OPPOSITE.
•ANALOGY –>
oWings of butterfly and of birds look alike.
oThey are not anatomically similar structures though they perform similar functions. This content developed by sciencegajab.com
oHence, analogous structures are a result of CONVERGENT EVOLUTION – different structures evolving for the same function and hence having similarity.
oOther examples of analogy
1.the eye of the octopus and of mammals
2.the flippers of Penguins and Dolphins.
oOne can say that it is the similar habitat that has resulted in selection of similar adaptive features in different groups of organisms but toward the same function:
oSweet potato (root modification) and potato (stem modification). –>Both food storage
•MOLECULAR SIMILARITIES –>
oSimilarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry.
oThese biochemical similarities point to the same shared ancestry as structural similarities among diverse organisms.
17.INDUSTRIAL MELANISM –> refers to the evolution of dark body colours in animal species that live in habitats blackened by industrial soot. The phenomenon has been documented in numerous species that hide from predators by blending in with their backgrounds. Peppered moths provide one example.
18.Evolution by anthropogenic action
•Herbicides, pesticides resistant varieties
•Antibiotics or drugs resistant organisms/cells
19.Evolution is NOT A DIRECT PROCESS in the sense of determinism. it is a STOCHASTIC PROCESS based on chance events in nature and chance mutation in the organisms.
20.ADAPTIVE RADIATION
•Darwin’s Finches –> Many varieties of finches in the same island–> evolved on the island itself (From 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.
•ANOTHER EXAMPLE IS AUSTRALIAN MARSUPIALS.
oA number of marsupials, each different from the other evolved from an ancestral stock, but all within the Australian island continent.
21.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).
22.BIOLOGICAL EVOLUTION
•Evolution by natural selection –> started when cellular forms of life with differences in metabolic capability originated on earth.
•The essence of Darwinian theory about evolution is natural selection.
•Nature selects for fitness fitness is based on characteristics which are inherited. Hence, 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 a 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
•French naturalist Lamarck –> “use and disuse of organs”.
•The work of Thomas Malthus on populations influenced Darwin.
•Natural selection is based on certain observations which are factual. For example, natural resources are limited, populations are stable in size except for seasonal fluctuation, members of a population vary in characteristics.
•Population sizes are limited–> due to competition for resources.
•Darwin asserted that variations, which are heritable and which make resource utilisation better for few (adapted to habitat better) will enable only those to reproduce and leave more progeny. This content developed by @sciencegajab.com
23.MECHANISM OF EVOLUTION
•Hugo DeVries
▪︎work on evening primrose
▪︎Mutation theory of evolution
•Mutations are random and directionless while Darwinian variations are small and directional.
•Evolution for Darwin was gradual while DeVries believed mutation caused speciation and hence called it SALTATION (single step large mutation).
24.HARDY-WEINBERG PRINCIPLE
•In a given population one can find out the frequency of occurrence of alleles of a gene or a locus.
•This frequency is supposed to remain fixed and even remain the same through generations. This content developed by @sciencegajab
•HARDY-WEINBERG PRINCIPLE –->allele frequencies in a population are stable and is constant from generation to generation.
•The GENE POOL (total genes and their alleles in a population) remains a constant. This is called GENETIC EQUILIBRIUM.
•Sum total of all the allelic frequencies is 1.
•p2+2pq+q2=1.
•When frequency measured, differs from expected values, the difference (direction) indicates the extent of evolutionary change.
•Disturbance in genetic equilibrium, or Hardy- Weinberg equilibrium, i.e., change of frequency of alleles in a population would then be interpreted as resulting in evolution.
•Five factors are known to affect Hardy-Weinberg equilibrium.
oGene migration or gene flow,
oGenetic drift,
oMutation,
oGenetic recombination and
oNatural selection.
•Migration –> gene frequencies change –> New genes/alleles are added to the new population and these are lost from the old population.
•There would be a GENE FLOW if this gene migration, happens multiple times.
•If the same CHANGE OCCURS BY CHANCE, it is called GENETIC DRIFT.
•Sometimes the change in allele frequency is so different in the new sample of population that they become a different species. The original drifted population becomes founders and the effect is called FOUNDER EFFECT.
•Natural selection is a process in which heritable variations enabling better
survival are enabled to reproduce and leave greater number of progeny.
•A critical analysis makes us believe that VARIATION due to mutation or variation due to recombination during gametogenesis, or due to gene flow or genetic drift results in changed frequency of genes and alleles in future generation.
•Coupled to enhance reproductive success, natural selection makes it look like different population.
•Natural selection can lead to
oSTABILISATION (in which more individuals acquire mean character value),
oDIRECTIONAL CHANGE (more individuals acquire value other than the mean character value) or
oDISRUPTION (more individuals acquire peripheral character value at both ends of the distribution curve)
25.A BRIEF ACCOUNT OF EVOLUTION
•2000 million years ago –> first cellular forms of life
•500 mya –> invertebrates were formed and active.
•Jawless fish probably evolved around 350 mya.
•Sea weeds and few plants existed probably around 320 mya.
•First first amphibians –> no specimens (No Fossils) ; ancestors of modern day frogs and salamanders.
•The amphibians evolved into reptiles.
•IMPORTANT CHARACTER –> Reptiles lay thick shelled eggs which do not dry up in sun unlike those of amphibians.
•350 mya –> Fish with stout and strong fins could move on land and go back to water.
oIn 1938, a fish caught in South Africa happened to be a Coelacanth which was thought to be extinct. These animals called lobefins evolved into the shapes and sizes dominated on earth.
•Giant ferns (pteridophytes) were present but they all fell to form coal deposits slowly.
•Some of these land reptiles went back into water to evolve into fish like reptiles probably 200 mya (e.g. Ichthyosaurs).
•The land reptiles were, of course, the dinosaurs. The biggest of them, i.e.,Tyrannosaurus rex was about 20 feet in height and had huge fearsome dagger like teeth.
•About 65 mya, the dinosaurs suddenly disappeared from the earth.
•The first mammals were like shrews.
•Mammals were more intelligent in sensing and avoiding danger at least. When reptiles came down mammals took over this earth.
26.ORIGIN AND EVOLUTION OF MAN
•About 15 mya,
o primates called DRYOPITHECUS and RAMAPITHECUS were existing.
o Hairy and walked like gorillas and chimpanzees.
o Ramapithecus was more man-like while Dryopithecus was more ape-like.
•Few fossils of man-like bones have been discovered in Ethiopia and Tanzania–> revealed hominid features leading to the belief that about 3-4 mya, man- like primates walked in eastern Africa. They were probably not taller than 4 feet but walked up right.
•Two mya AUSTRALOPITHECINES
o probably lived in East African grasslands.
o they hunted with stone weapons but essentially ate fruit.
•Homo habilis
o the first human-like being the hominid
oThe brain capacities were between 650-800cc.
oThey probably did not eat meat.
•Homo erectus
oFossils discovered in Java in 1891 revealed the next stage,
oEvolve about 1.5 mya. This content developed by
ohad a large brain around 900cc.
oHomo erectus probably ate meat.
•The Neanderthal man
o brain size of 1400cc
olived in near east and central Asia
obetween 1,00,000-40,000 years back.
oThey used hides to protect their body and buried their dead.
•Homo sapiens
o arose in Africa and moved across continents and developed into distinct races.
oDuring ice age between 75,000-10,000 years ago modern Homo sapiens arose.
oPre-historic cave art developed about 18,000 years ago.
oAgriculture came around 10,000 years back and human settlements started.
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