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Evolution • Theory- a well-supported testable explanation of phenomena that have occurred in the natural world. • Evolution- Change over time; modern organisms have descended with modification from ancient organisms. Because it is supported by so many lines of evidence, evolution is no longer considered a hypothesis. Evolution is one of the great unifying theories of biology What was Charles Darwin’s contribution to science? • At 22, sailed on the “HMS Beagle” to the Galapagos Islands. • Was going to school to be a minister-believed God created each species to match its habitat and they never changed. • Thought Earth was about 6,000 years old and didn’t change. • During journey, he made observations and recorded them in a journal. • Darwin began to doubt that species remained “constant.” Darwin’s Background Voyage • Darwin's many observations led him to the idea that species slowly change over time • Darwin's comparison of the animals of South America and the Galapagos Islands caused him to conclude that adaptation to the environment can cause diversification, including origin of new species • Examples: Patagonian hares replaced rabbits in the South American grasslands The Galapagos Islands Island species varied from the mainland species, and from island-to-island Each island had either long or short necked tortoises depending on the island's vegetation Darwin’s Observations Contd. Finches found only on the Galapagos Islandsresembled a mainland finch, but there were more types Beak shapes are adaptations to different means of gathering food (what the finches eat) Galapagos finch species varied by: nesting site beak size eating habits The Galapagos Islands The diagram below presents 10 species of finches on the Galapagos Islands, each filling a different niche on various islands. All of them evolved from one ancestral species Each species evolved from the same ancestor through process of geographic isolation • In 1859, Darwin published “The Origin of Species.” • His book stirred up controversy. • Proposed **EVOLUTION OCCURRED BY NATURAL SELECTION • Organisms have more offspring than can survive. • Certain individuals are more likely to survive than others (survival of the fittest.) • Species DO change over time. • Gradual changes may cause members of one species to eventually evolve into new species. • African apes are close genetic relatives of modern humans. Darwin’s Insights Members of each species vary from one another Artificial selection- selection by humans for breeding of useful traits from the natural variation among different organisms Artificial selection is used to breed animals with the trait of interest In artificial selection, nature provided the variation, and humans selected those variations that they found useful Lots of change can be achieved in a relatively short time Artificial Selection What ideas shaped Darwin’s thinking? Hutton and Lyell helped scientists recognize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present Hutton and Lyell proposed that geological processes have shaped the Earth, ex. Rain LaMarck’s Theor • Jean Baptiste LaMarck: 1800’s – Believed: • Change Occurs Over Time • Inheritance of acquired characteristics – acquired changes were passed to offspring • Law of Use and Disuse – If a body part were used, it got stronger – If body part NOT used, it deteriorated • Examples: Body builders or pierced ears Thomas Malthus • 19th century English economist Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone Darwin’s Principles of Natural Selection Natural selection is the mechanism by which evolution occurs 1. Variations exist between individuals in a species. 2. Variations are inherited from parents. 3. Populations produce more offspring than can survive on the available resources. 4. Variations that increase reproductive success will be more common in the next generation. Given enough time, natural selection could modify a population enough to produce a new species. Darwin’s Evidence for Evolution 1. Fossil record -fossils are remains or imprints of living things -different layers of rock were formed at different times in Earth’s history -comparing fossils from older layers to fossils from younger layers shows that organisms change over time Darwin’s Evidence, continued 2. Geographic Distribution of Living Species - geographically separate, similar species (like finches) descended with modifications (changes) from a common ancestor -geographically separate, similar environments gave rise to different species that had similar anatomy and behavior 3. Comparative Anatomy Homologous body structures: -structures that have different mature forms but develop from the same embryonic tissues -have strong structural similarities between different species -adapted in different ways to help survive in different environments -provide strong evidence that there is descent from common ancestors -vestigial structure is a trace of homologous structures that have little or no function Anatomical Evidence cont. Analogous structures – different structures that are inherited from different ancestors and have come to resemble each other because they serve a similar function • Do not come from the same evolutionary origin • Ex: wings of birds vs. wings of insects • Ex: fins of fish vs. flippers of whales Different structure, same function! 4. Comparative Embryology: -there are many similarities in embryos of many vertebrate animals -provides strong evidence of common ancestry 5. Comparative Biochemistry -common ancestry can be seen in complex metabolic molecules -species that share a recent common ancestor share some amino acid sequences -the more closely related the species are, the more sequences will be shared -this has been found to be true with cytochrome c, an enzyme essential for respiration in animals -similar patterns have been found in other proteins as well as in DNA and RNA Adaptation • The concept of adaptation underlies Darwin’s theory of natural selection. • An adaptation is a trait shaped by natural selection that increases an organism’s survival or reproductive success. (Fitness) • Examples: – Camouflage: blend with surroundings – Mimicry: look like another species – Antimicrobial resistance: in bacteria Population Genetics • Evolution occurs at the population level, not the individual. Genes are the raw material for evolution. • Evolution won’t occur in a population unless the frequencies of alleles are acted upon by forces that cause change. • (Constant allele frequencies = genetic equilibrium) Disruptions to Genetic Equilibrium (Mechanisms of Evolution) • Genetic Drift: any change in the allele frequencies that is due to chance. It has the greatest effect in small populations due to the small gene pool size. – Founder Effect: extreme example of genetic drift. Occurs when a small part of a population becomes isolated from the rest of the population. The random subset of alleles in the small population may become more common, and result in genetic variations in the separated populations. Examples: Amish communities with polydactyly and dwarfism. – Bottleneck: extreme example of genetic drift. Occurs when a population declines to a very low number and then rebounds. Gene pool of the rebound population is genetically similar to the lowest level of population—it lacks diversity. • Gene flow: New genes entering the population and other genes leaving the population as individuals randomly move (migrate) between populations. • Nonrandom mating: Organisms usually mate with individuals in close proximity. This can lead to inbreeding and a change in allele frequencies. • Mutation: a random change in genetic material. The cumulative effect of mutations in a population might cause a change in allele frequencies. Beneficial mutations could be selected for, and become more common in subsequent generations. • Natural selection: acts to select the individuals best adapted for survival and reproduction. It acts on an organism’s phenotype, and changes allele frequencies. Speciation Speciation is the formation of new species. A species is a group of organisms that can breed with one another and produce fertile offspring. This means that individuals of the same species share a common gene pool, and a genetic change that occurs in an individual can spread throughout the population as that individual and its offspring reproduce. Speciation continued For a species to evolve into two new species, the gene pools of the two populations must become separated. This means the populations must be reproductively isolated: the members of the two populations can’t interbreed and produce fertile offspring. There are several ways reproductive isolation can occur. Speciation, continued 1. Behavioral Isolation: -two populations are capable of interbreeding but have different courtship rituals or reproductive strategies that involve behavior 2. Geographic Isolation: -two populations are separated by geographic barriers -this can result in separate gene pools Speciation, continued 3. Temporal Isolation: -two or more species reproduce at different times Once the populations are isolated, natural selection works on each population differently, eventually resulting in enough differences so that successful interbreeding can’t occur. At this point, the populations are separate species. Patterns of evolution • Adaptive radiation – Also called divergent evolution – Occurs in a relatively short time when one species gives rise to many species in response to creation of new habitat or other ecological change – Example: rise of the mammals after the extinction of dinosaurs • Coevolution – Species evolve in close relationship with other species—evolution of one affects the other – Examples: can be mutually beneficial, can be parasitic • Convergent evolution: – Unrelated species evolve similar traits in different parts of the world – Occurs in ecologically similar environments that are geographically separate Rates of Speciation • Gradualism: evolution proceeds in small, gradual steps • Punctuated equilibrium: long periods of no changes are punctuated by short, rapid periods of genetic change