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Transcript
•The Earth has millions of organisms that display different characteristics and traits. This variety of living things is called biological diversity. How did all of these different organisms arise? How are they related? The Evolutionary Theory explains these questions by using observations, scientific facts, and hypotheses. Evolution, or change over time, is the process by which modern organisms have descended from ancient organism. A theory is a well supported testable explanation of phenomena that have occurred in the natural world. Charles Darwin Charles Darwin was one of the first scientists to develop a theory of evolution. His theory was based on observations he made while sailing around the world in 1831 on the H.M.S Beagle. Darwin noticed that when he visisted different geographical locations he saw similar species. Even though many of these locations were separted by long distances organisms that lived in similar environments had similar characteristics. Darwin also noticed that some environments, like Australia, had unique organisms that were found nowhere else in the world. Darwin also examined fossils and found that some extinct organisms were similar to living species. One of the focal points of his journey was the Galapagos Islands off the west coast of South America. The Galapagos Islands at the time were fairly isolated from the mainland of Ecuador and Peru. Within the island chain there was significant differences between each island . Hood Island, for example, had sparse vegetation and was extremely hot. Isabela Island had rich vegetation that animals could easily reach. Darwin noticed that animals on each of the Islands were well suited to survive and flourish according to the conditions on that specific island. Some animals were similar, but they occupied different habitats on one island. These observations started his thinking toward how these animals became so well adapted. The central theme in Darwin’s theory of evolution is the concept of natural selection. Natural selection deals with an organism struggle for existence, meaning that members of each species compete regularly to obtain food, living space, and other necessities. In natural selection, those variations in the genotype that increase an organism’s chances of survival and reproduction are preserved and multiplied from generation to generation. The ability of an individual to survive and reproduce in its specific environment is called fitness. An adaptation is any characteristic that increases an organism’s chance of survival or reproduction. The struggle for existence, fitness, and adaptation lead to the concept of survival of the fittest. Over time, natural selection results in changes in the inherited characteristics of a species’ fitness in its environment. Great White Shark Giant Anteater How have these animal adapted to their environment, or changed over time to become successful? Darwin’s Theory of Evolution can be summarized. 1. Individual organisms in nature differ from one another. Some of this variation is inherited. 2. Organisms in nature produce more offspring than can , survive and many of those that survive do not reproduce. 3. Because more organisms are produced that can survive, members of each species must compete for limited resources. 4. Because each organism is unique, each has different advantages and disadvantages in the struggle for existence. 5. Individuals best suited to their environment survive and reproduce most successfully. The characteristics that make them best suited to their environment are passed down to the offspring. 6. Species change over time. Over long periods of time natural selection causes changes in the characteristics of species. 7. Species alive today have descended with modifications from species that lived in the past. 8. All organisms on Earth are united into a single tree of life by common descent. •The formation of a new species is called speciation. Recall that biologists define a species as a group of organisms that breed with one another and produce fertile offspring. This means that individuals in the same species share common traits. If those traits increase fitness, than the traits will eventually be found throughout the population. Genes lead to Speciation and Evolution New species form due to the genetic variation in the entire population. Members of the same population interbreed so they . share a common pool of genes aka: Gene Pool Gene pools consist of all genes, including all the different alleles for each gene that are present in a population. Allele frequency is the number of times an allele occurs in a gene pool, compared to the total number of alleles in that pool for the same gene. As allele frequencies change the overall population may start to look a little different. A few different types of scenarios may start to occur Directional Selection One phenotype (appearance) is more favorable Example is the industrial melanism in moths during the industrial revolution . Stabilizing Selection The "in between" phenotype is the best. Example is birth weigh between 6 and 9 pounds Disruptive/Diversifying Selection The "in between" is less common. As new species evolve, populations become reproductively isolated from each other. When the • members of two populations cannot interbreed and produce fertile offspring, reproductive isolation has occurred. The sharks above are related but unable to mate and produce offspring therefore they are members of two different species. Reproductive isolation can develop in a variety of ways including behavioral isolation, geographic isolation, and temporal isolation. Behavioral isolation: occurs when two populations are capable of interbreeding but have differences in courtship rituals or other behaviors. Geographic isolation: occurs when populations are separated by geographic barriers such as rivers, mountains, or bodies of water. Temporal isolation: occurs when two or more species reproduce at different times. For example, three similar species of orchid all live in the some rain forest, and they all reproduce at different times of the year. Speciation in Darwin’s Finches •Speciation in the Galapagos finches occurred by founding of a new population, geographic isolation, changes in the new population’s genes, reproductive isolation, and ecological competition. 1.) Founders Arrive: Many years ago, a few finches from the mainland of South America arrived on one of the Galapagos Islands. These birds may have gotten lost or were blown off course by a storm when flying. They managed to survive on the island. 2.) Separation of Populations: Later on, some birds from Species A crossed to another island in the Galapagos chain. These birds do not usually fly over open water therefore the birds on the two islands were isolated from each other. 4.) Reproductive isolation: The two populations change some much over time that if birds from island B went back to island A they would not mate with the island A birds. . This is reproductive isolation, and the formation of two different species, A and B. 3.) Changes in the Genes: Over time the two populations on the different islands adapted to their local environments. Each island offered different food sources and over this long period of time the Finches evolved differently to deal with this. As the finches competed for food and space there was more migration and speciation until multiple species of finches existed. Today there 13 different species of finches on the Galapagos Islands. Patterns and Processes of Evolution Evidence shows that evolution has often developed at different rates for different organisms at different times over the long history of life on Earth. Gradualism: Gradualism is the concept that organisms evolve in a slow and steady manner and acquire changes over long periods of time. Punctuated Equilibrium is term used to describe rapid periods of change that occur in a relatively short period of time (remember a short period of geologic time could be thousands of years). Patterns of evolution become evident when fossil records and Two patterns of evolution that we will cover include Adaptive Radiation and Convergent Evolution. observations are analyzed. Adaptive radiation-Divergent Evolution ordinarily involves the development of new species in the new environments from a common ancestor. The most common situations which result in adaptive radiation occur following mass extinctions, or when species move into new, unoccupied regions. Convergent evolution In evolutionary biology, convergent evolution is the process whereby organisms not closely related, independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. Coevolution: Coevolution is a change in the genetic composition of one species (or group) in response to a genetic change in another. The classic analogy is the coevolutionary arms race: a plant has chemical defenses, an insect evolves the biochemistry to detoxify these compounds, the plant in turn evolves new defenses that the insect in turn "needs" to further detoxify. 1.) Biogeography: Patterns in the distribution of living and fossil species tell us how modern organisms evolved from their ancestors. Darwin noticed two things, first, closely related species differentiate (change) in different environments. The second pattern he noticed was that very distantly related organisms developed similar traits when they were in the same environment. 2.) Fossil Records: Many recently discovered fossils form a series that traces the evolution from modern species to extinct descendants. 3. Comparing Anatomy: Darwin suggested that animals with similar structures evolved from a common ancestor with a basic version of that structure . Structures that are shared by related species are called homologous structures. Homologous structures adapted to different purposes as the result of decent with modification. Homologous traits have similar structure and similar function. Darwin also noticed the presence of analogous traits . Analogous traits are traits that have similar function but completely different structure. 4.) Genetic and Molecular Biology: Genetic research has allowed us to determine that many organisms have multiple genes in common, for example, cytochrome C. The more genes that two organisms have in common the closer they are on the evolutionary tree.