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Evolution Chapters 16,17,19.2 1
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Voyage of the Beagle- (1831-1836) Charles Darwin (1809 - 1882) While ship was docked, Darwin would make observations about the plant and animal life Kept a journal of his observations. Noted 3 distinctive patterns of Biological Diversity: 1. Species vary globally 2. Species vary locally 3. Species vary over time The Galapagos Islands – close together, but had different environments and different animals and plants tortoise shell and finch beak 2
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Charles Darwin Observations Finch Beak Tortoise Shell 3
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Voyage of the Beagle- (1831-1836) Charles Darwin (1809 - 1882) Living Organisms and Fossils Darwin collected fossils, once living organisms, and noted that some fossils of extinct animals were similar to some living species, while others were different. 4
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Contributions to Theories of Evolution Evolution – a change over a long period of time. Theory – a well supported, testable explanation of phenomena Geology and Fossils Lyell (1785) & Hutton (1833) helped shape Darwin’s research Helped scientists recognize that earth is millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present Uniformitarianism: Processes that change Earth in past are same as today 5
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Contributions to Theories of Evolution Living Organisms Change Lamarck (1809) Proposed that organisms could change during their lifetime by selectively using or not using various parts of their bodies. Also suggested that individuals could pass these acquired traits on to their offspring, enabling species to change over time. Stated organisms have an inborn drive to become perfect. Lamarck incorrect: Organisms do not have a tendency towards perfection Acquired traits can not be passed on to offspring 6
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Contributions to Theories of Evolution Population Growth Malthus (1798) If the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone. More births than deaths. Applied to plants and animals more than to humans Human populations limited by: Limited resources Adverse conditions Artificial Selection 8
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Charles Darwin “On The Origin of Species” Prompted to publish by Alfred Russel Wallace Published a short essay in 1958 Darwin published in 1859 Proposed the mechanism for evolution Evolution has been taking place for millions of years- and continues in all living things 9
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Inherited Variation and Artificial Selection In artificial selection, nature provides the variation, and humans select those variations that they found useful Selectively breeding only the largest hogs, fastest horses, or cows that produce most milk. 10
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Evolution by Natural Selection 1. The struggle for existence Members of each species compete regularly to obtain food, living space and other necessities of life. 2. Variation and Adaptation Result of adaptations- inherited characteristic that increases an organism’s chance of survival 3. Survival of the fittest – how well you can survive and reproduce. 4. Natural selection Over time, natural selection results in changes in inherited characteristics of a population 5. Descent with modification Todays organisms look different than their ancestors because the changes are inherited. 11
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Adaptations 12
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Natural Selection 13
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Evidence of Evolution 1. Fossil Record Remains of ancient life Different layers of rock formed at different times Trilobite 2. Biogeography = Geographic Distribution of living species Existence of similar but unrelated living organisms. Island Finches- descendants with modifications from common mainland ancestor. 14
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Evidence of Evolution 3. Homologous body structures Structures that are shared by related species and that have been inherited from a common ancestor. Structures that develop from same embryonic tissue. Same structure but different function! 15
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4. Analogous structures – Body parts that share a common function, but not structure. 16 Evidence of Evolution
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5. Vestigial Structures – inherited from ancestors but have lost much or all of their original function due to different selection pressures acting on the descendant. 17 Evidence of Evolution
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6. Embryology – Similar patterns of embryological development provide further evidence that organisms have descended from a common ancestor. 18
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Summary of Darwin There is variation in organisms (which is heritable). Organisms produce more offspring than can survive. There is competition for limited resources. Natural selection is always taking place.(Those that are most “fit” survive to reproduce, and those that are not, die. Species living today are descended, with modification, from ancestor species. 19
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Chapter 17 Evolution of Populations 20
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Evolution of Populations Combined the work of Mendel and Charles Darwin in the 1930’s Populations, not individual organisms, evolve. Fitness is an organism’s success in passing genes to next generation. 21
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Evolution is a change in the relative frequency in a gene pool. Gene pool : all genes including the different alleles that are present in a population Allele frequency : Number of times that the allele occurs in a gene pool, compared to the total number of alleles in that pool for the same gene. 22
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Sources of genetic Variation 1. Mutations Any change in the sequence of DNA of a cell. Could be a gene change or a chromosomal change. Most mutations are neutral. 2. Genetic Recombination in Sexual Reproduction Individuals are not exact copies of parents. Crossing over and independent assortment during meiosis occurs creating more variety among gametes. 23
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Single and Polygenic Genes Single gene trait- Controlled by one gene that has two alleles Polygenic trait- controlled by two or more genes Height Skin color Eye color 24
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Natural Selection on Single Gene Traits Lead to changes in allele frequency and thus changes in phenotypic frequencies hence evolution. A brown lizard experiences a mutation that produces red and black forms What would happen? Why did the back lizard grow in population size? 25
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Natural Selection on Polygenic traits. More complex then single-gene traits Phenotypes can be affected in three ways: 1. Directional selection Individuals at one end of the curve have higher fitness Some individuals fail to survive/reproduce Bell curve will shift in either direction depending on the favorite. 26
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Natural Selection on Polygenic traits. 2. Stabilizing selection Individuals near the center of the curve have higher fitness Bell curve doesn’t move, but narrows Birth Weight 27
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3. Disruptive selection When individuals at both ends of the curve are fitter than individuals in the middle. Bell curve dips in the center, acts against the intermediate type. Bird Seed 28 Natural Selection on Polygenic traits.
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29 Natural Selection on Polygenic traits.
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Genetic Drift Natural selection is not the only source of evolution Genetic Drift- changes in the allele frequency due to a random event or by chance. Only in small populations 2 types 1. Bottleneck effect – a natural disaster or disease can dramatically reduce the size of a population 2. Founder effect – the allele frequencies change as a result of the migration of a small subgroup of a population. - Colonizing a new habitat 30
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Hardy-Weinberg equilibrium Genetic Equilibrium - allele frequencies in its gene pool do not change. If allele frequency remains same: population won’t evolve Hardy-Weinberg predicts 5 Conditions that can disturb genetic equilibrium and cause evolution to occur: 1. Small population size - genetic drift occurs, a small population will be impacted over a large population. 2. Non-Random mating - selection of mates regardless of their traits. 3. Mutations – introduce new alleles into the gene pool. 4. Immigration or emigration – introduce new alleles or remove alleles from a population. 5. Natural selection – different genotypes and phenotypes have a different fitness. 31 5 fingers of evolution video
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Formation of Species: Speciation Species – can interbreed and produce fertile offspring. When the members of two populations cannot interbreed and produce fertile offspring Example: Mule Horse + Donkey Speciation – the formation of a new species Reproductive Isolation – A population has split into two groups, and the changes in one of those gene pools cannot spread to the other and the two groups can no longer breed. 3 Mechanisms for Reproductive Isolation to occur: 1. Behavioral Isolation - Can interbreed, but have developed different mating rituals 2. Geographic isolation - Separated by geographic barriers such as rivers, mountains, lakes, etc. 3. Temporal Isolation - Reproduce at different times 32
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Speciation in Darwin’s Finches 1. Founders Effect Birds arrive to islands from mainland 2. Geographic Isolation On different islands 3. Changes in gene pool Overtime, each finch became adapted to local environment 4. Behavioral reproductive isolation Don’t have desirable traits or courtship rituals to other finches. 5. Competition & Continued Evolution Natural selection 33
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Ch 19.2 Patterns of Evolution 1. Extinction 99% of all species are extinct. Why? 2. Gradualism A slow, steady change in a particular line of descent. 3. Punctuated Equilibrium Involves stable periods interrupted by rapid changes. 34
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Patterns of Evolution 3. Adaptive Radiation The process by which a single species or a small group of species evolve over a short time into several different forms that live in different ways. 4. Convergent Evolution Evolution produces similar structures and characteristics in distantly related organisms. Unrelated organisms resemble each other Examples: Penguin (Bird), Dolphin (Mammal), Shark (Fish). 35
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Patterns of evolution 5. Coevolution Two specifies evolve together in response to changes in each other over time. The evolution of organisms that are ecologically connected to each other and can’t survive without each other. As one evolves, the other will evolve with it Acacia tree and fire ants Bees Pollinate the flowers 36
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