Artificial Selection .Man has domesticated many wild animals & plants - He has also selected many plants & animais and carid out intensive breeding programs to raise new varieties of plants and animals for agriculture, horticulture, sport or security. He has raised a number of high- yielding breeds of animals (like cows, buffalo, poultry birds etc.) & crops (like varieties of wheat, rice, maize, pulses, etc.) .
Adaptive Radiation Adaptive ration is an evolutionary process in which an ancestral stock gives rise to new species in a given geographical area, starting from a point & literally radiating to other geographical areas or habitats . 1. Eg., 1 Darwin's finches . These were small black birds which Darwin observed in Galapagos islands There were many varieties in the same island. He reasoned that after originating from a common ancestral seed eating stock, the finches must have radiated to different geographical areas & undergone adaptive changes, especially in the type of beak. Living in isolation for long, the new kinds of finches emerged that could function & survive in the new habitats. . . .
Large ground finch (seeds) Cactus ground finch (cactus fruits and flowers) Vegetarian finch (buds) Woodpecker finch (insects)
E.g., 2 Australian marsupials. . A number of marsupials (pouched mammals) each different from the other, evolved from an ancestral stock within Australia. When more than one adaptive radiation appeared to have occurred in an isolated geographical area with different habitats, it can be called as convergent evolution. Placental mammals of Australia show parallel evolution as they have evolved from other marsupial mammals, each of which closely resembles & looks similar to a corresponding marsupial. Parallel evolution of Australian Marsupials & Placental Mammals are given below: . S.No Australian Marsupial 1. 2. 3. 4. 5. 6. 7. Marsupial mole Numbat (banded ant eater) Marsupial Mouse Spotted cuscus Flying Phalanger (sugar glider) Tasmanian tiger cat Tasmanian Wolf Placental Mammal Mole Ant eater Mouse Lemur Flying squirrel Bobcat Wolf
Convergent Niche Placental Mammals Australian Marsupials Evolution BurrowerMo Marsupial mole Anteater Lesser Numbat (anteater)- anteater Marsupial mouse Mouse Mouse Spotted cuscus Climber Lemur Glider Flying Flying squirrelphalanger Cat Tasmanian "tiger cat Ocelot Wolf Tasmanian wolf Wolf
Lamarck's Theory of Evolution . According to Lamarck, the evolution of life forms had occurred by the use & disuse of organs. Organs that are used more develop more while those that are not . used, become vestigial in the long run. The character/ adaptation developed by an organism during its life time is passed on to the progeny He gave the long neck of giraffe as an example; according to him, it is an outcome of the attempt to stretch their neck continuously to eat leaves from tall trees. As they passed on this acquired character of long neck to succeeding generations, giraffes came to acquire long neck over long period of time. . . .
and stretching until neek becomes progressively longer LAMARCK'S GIRAFFE Keeps stretching neck to reach leaves higher up on tree and stretching Original short neeked' aneestor Driven by nr"need"
Mutations- The Cause of Evolution . Hugo de Vries proposed the mutation theory of evolution; he worked on evening primrose. He defined mutation as large heritable change occurring suddenly in the characteristics of a population. .According to him mutation caused speciation and called it as saltation, i.e., single- step large mutation He differed from Darwin in the following ways . i. De Vries' mutation are random & directionless, while Darwinian variations are small & directional. i. De Vries believed that such large, single- step mutation (called saltation) caused speciation, but evolution for Darwin is gradual & occurs over a number of generations.
Hardy- Weinberg principle This principle states that under certain conditions of stability, the alleles frequencies of a population are stable & remain constant from generation to generation in sexually reproducing organisms, this stability is called genetic equilibrium or Hardy- Weinberg equilibrium. . he is one & itis represeantea as. (p+q)2 or p2+2pq+q2 1 Disturbance in the genetic equilibrium is considered as evolutionary change Five factors affects Hardy- Weinberg equilibrium namely- Gene Migration, Genetic Drift, Mutation, Recombination & Natural Selection . .
1. Gene Migration: When some individuals of a population migrate to other populations, or when certain individuals come into a population, the gene frequencies of the given population change, i.e., some genes are lost in the first case & added to the second. If this migration occurs a number of times, gene flow occurs 2. Genetic Drift: Random changes in the allele frequencies of a population occurring by chance, constitute genetic drift The change in allele frequency may become so drastically different that they form new species. The original drifted population becomes the founder & the change in the phenotype & genotype of the progeny, constitute the founder effect This is clear with microbial experiments, where he pre- existing advantageous mutants get selected & over a few generations speciation occurs . . .
Natural selection process depends on the traits favoured & produce one of the three following effects: Stabilization- in which more individuals acquire mean character value, i.e., variation is much reduced Directional change, in which more individuals acquire value other than the mean character value. Disruption, in which more individuals acquire peripheral character value at both ends of the distribution curve. . 1. 2. 3.