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Notes #1 Patterns, Processes, & Rates of Evolution Adaptations are traits that help living organisms survive. Different organisms in a species have different traits. These differences are called variations. How do variations occur? Mutations Rearrangement of genetic material during sexual reproduction Mutation Can be helpful, harmful, or have no effect at all. If an organism’s environment changes and it happens to have a mutation (adaptation) which allows it to survive in its new environment, it will. If not, it will die. Draw this diagram Speciation Remember: A species is a group of organisms that share similar characteristics & can interbreed to produce fertile offspring. Remember: All the members of a species that live in an area at the same time make up a population. Over time, variations that arise within a population as a result of natural selection can have two major outcomes: speciation or extinction. Speciation is the evolution of a new species from an existing species. One species can evolve into another if the environment changes. Examples of Speciation If the environment becomes colder, animals with the inherited trait for thicker fur would be better to survive, reproduce, & pass this trait on to their offspring. If a new predator moves into an area, the organisms it preys on that have longer legs to help them escape the predator are more likely to survive and reproduce. Land of Whoa~~Storytime! So listen up! Events that can lead to speciation A barrier forms that separates numbers of a species; this is called geographical isolation Two groups are in different environments Groups begin to show different traits as a result of natural selection; this is called divergent evolution GEOGRAPHIC ISOLATION OCCURS WHEN A POPULATION BECOMES SEPARATED BY CHANGES IN THE ENVIRONMENT. AFTER SEVERAL GENERATIONS, ISOLATED ORGANISMS MAY CHANGE ENOUGH TO FORM A NEW SPECIES Mechanisms of Evolution through genetic variation Mutations Caused by errors during DNA replication or by damage to DNA from environmental factors such as radiation. To affect evolution, mutations must be passed from one generation to the next. Only mutations in gametes can be passed to offspring & have the potential to affect evolution. Mechanisms of Evolution through genetic variation Gene flow – the introduction of genes from one population into the gene pool of another population Gene pool- combined genetic information of all members of a population The most significant factor that affect gene flow is mobility (movement). For example, animals are more mobile than plants & tend to have a higher rate of gene flow. Rates of Evolution Two main views: gradualism & punctuated equilibrium Rates of Evolution: Gradualism Theory that evolution occurs over a long period of time. Change is slow & constant. This is how Darwin thought natural selection worked. Rates of Evolution: Punctuated Equilibrium Theory states that evolution occurs in spurts. A period of rapid speciation will be followed by a long period of time in which little or no change occurs. Supporters of this theory believe that the periods of rapid change are caused by either random changes in DNA or large, sudden changes in the environment. Scientists who favor punctuated equilibrium theory often point to the Cambrian explosion to support their views. Cambrian Explosion Period of geologic time, about 530 million years ago, when most of the major groups of complex animals appeared on Earth. Fossil record shows few fossils before this time. Mostly of simple organisms. During the Cambrian explosion, a much larger number of fossils of more complex animals appeared in a short time. Extinction Permanent loss of a species Can happen slowly as populations fail to adapt in the environment die without producing offspring or produce fewer offspring in each generation. Quickly by Mass extinction – loss of huge numbers of species in a fairly short period of time Examples of Mass Extinctions Occurred at the end of the Permian period About 250 million years ago 96% of all ocean invertebrates became extinct Examples of Mass Extinctions Occurred at the end of the Cretaceous period Killed 60-75% of ocean species Dinosaurs Mass extinctions make it possible for new species to evolve and thrive. QUIZ TIME! 1. The evolution of a new species from an existing species is called a. mass extinction c. biodiversity b. speciation d. gradualism 2. Gradualism is the theory that evolution occurs over a _______________ period of time. a. short b. long #3 Which of the following best describes the theory of punctuated equilibrium? a. Biological change occurs slowly and steadily over a long period of time. b. Biological change occurs quickly over a short period of time and is followed by long periods of little or no change. c. Tiny changes in a species add up to major changes over time. d. Events throughout the history of life have caused the extinction of species. 4. Earth has experienced several ice ages. Which type of organisms would natural selection favor if Earth had another ice age? a. organisms that swim b. organisms that are predators c. organisms that carry out photosynthesis d. organisms adapted for surviving cold temperatures Checks Your Answers 1. b 2. b 3. b 4. d