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Evolution (part3)
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All important topics releated to this chapter.

Shivam Sharma
Learning and teaching Biology, pursuing medical studies at TU.

U
Unacademy user
Anupam sir...please add on more lectures on this series...this is my fav.series.
Anupam Mishra
a year ago
Yes Sonu. There will be more lessons in this series for sure. 🙂
  1. EVOLUTION


  2. Comparative Anatomy & Morphology: . Comparative anatomy and morphology shows both similarities & differences among the present day organisms & those existed long before. i. Homology Homology is the relationship among organs of different groups of organism, that show similarity in the basic structure and embryonic development, but perform different functions. Homology of organs of different organisms indicates their common ancestry Homology is found in the bones of forelimbs of whales, cheetah, birds, amphibians and human; they have similar basic anatomical structure with the bones humerus, radius, ulna, carpals, matacarpals & phalanges The thorns of Bougainvillea & tendrils of Cucurbita represents homology . .


  3. Homology/ homologous organs are the result of divergent evolution, i.e., the evolutionary process where the same structure develops along different directions due to adaptations for different needs. Thorn 8. Fipper of Se for S Wing of Bird for Patagf Foralimb ofman rm Rying Bat for flying Harse for Running for Grpin Bougainvillea Cucurbita


  4. ii. Analogy Analogy is the relationship among organs of different groups of . organisms pertforming the same function,irrespective of structural or anatomical differences. Eg.- Eyes of octopus & those of mammals; wings of butterfly & those of birds; flippers of whales or dolphins & those of penguins; tubers of sweet potato (root modified) & those of potato (stem modified) . Analogy is the result of convergent evolution, i.e., the evolutionary process, where anatomically different structures in different groups of organisms evolve towards the same function. It is the similar habitat conditions that have selected similar adaptive features in different groups of organisms towards the same function. .


  5. Eyeas Comea Iris Cilary Lens Retina Optic nerve Optic gangion Human eye Octopus eye The wings of butterflies and birds are analogous structures Tuber of potato Tuber of sweet potato


  6. Molecular Homology: Molecular homology refers to the similarities in the biomolecules of different groups of organisms. The sequences of nucleotides in nucleic acid & many proteins are similar in apes & humans The biochemical similarities point to the same/ common ancestry of diverse organisms Biogeography: . The differential geographical distribution of different organisms also indicates common/ shared ancestry in that restricted region. Habitat isolation has probably restricted these organisms to particular geographical regions on the earth. .


  7. Theory of Natural Selection Darwin made a sea voyage round the world in a sail ship, named H. M. S Beagle Based on the observations he made during this voyage, he concluded the following: i. The existing living organisms share similarities to varying degrees not only among themselves but also with the life forms that existed millions of years ago. There has been gradual evolution of life forms during different periods of geological history and there has been extinctions also. ii. ii Any population has built- in variations in characteristics. iv. Individuals with those characteristics which enable them to survive better (fitness of the individual) in the natural conditions, would overcome the others, who are less adapted under the same natural conditions


  8. This fitness of individual, according to Darwin refers ultimately and only to reproductive fitness. Such fit individuals leave more progeny (with more fit individuals) than others. They are selected by nature (natural selection) to survive and reproduce to increase their population size. Branching descent and Natural selection are the two key concepts of Darwinian theory of evolution. Darwin considered natural selection as a mechanism of evolution. . . Alfred Wallace was a naturalist during Darwin's time concluded: i. New life forms arise & evolve in due course of time ii. All the existing forms of life share certain similarities & common ancestors ii. These ancestors lived at different periods in the history of earth. iv. The geological history closely correlates with the biological history.


  9. The rate of appearance of new life forms is linked to the life- cycle or lifespan of organisms; e.g., Microbes that divide fast (with a generation time of 20 minutes or so) speciation can occur within a few days, whereas in larger animals it would take millions of years as their life span are in years. The term fitness has a genetic basis for getting selected & to evolve Adaptive ability is inherited & has a genetic basis Fitness is the end result of the ability to adapt & get selected by nature. Natural selection is based on certain observations, which are factual; they are as follows: . . . i. Natural resources are limited; so populations are stable in size except for seasonal fluctuations Members of the population show variation of every characteristic- no two members of a population are identical, even though they show similarities ii.


  10. ii. Theoretically population size will grow exponentially, if everybody reproduced to the maximum capacity- it is seen in growing bacterial/ microbial populations. The population size in reality is limited, it is due to competition among individuals for resources & only those which are betted adapted could survive and reproduce at the cost of others who are less adapted to that habitat. iv. The insight of Darwin was that he asserted that the heritable variations which make resource utilization better in some individuals will enable them to reproduce & leave more progeny over a period of time; over many generations, there would be change in the population characteristics leading to origin of new forms/ species i.e., speciation .


  11. The obtained study was compared with areas where industrialization did not occur e.g., in rural areas, the count of melanic moths was low. Conclusion: In a mixed population, individuals that are better adapted, can survive & reproduce in large numbers & increase their population size & no variants was completely wiped out . . lichen-covered trunk lichen-free, soot-covered trunk