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Transcript
Evolution for Beginners Let’s Start From the Basics • Some organisms adapt to their conditions, whether it be physical or a behavior. Differences Among Organisms • Organisms that share the same characteristics are considered a species. ex. Homo sapiens (humans) In order for an organism to be considered a species (scientifically), they must be able to reproduce offspring that can also reproduce. Do Organisms Change Over Time? Think: Have all species that are found on Earth today always existed? (keep in mind that Earth is 4.6 billion years old) What is evolution? A basic definition of evolution… The process by which populations gradually change over time…. So what does the definition mean? • Evolution is a change in the number of times specific genes that code for specific characteristics occur within an interbreeding population • Individuals don’t evolve, populations do • There is no implied “improvement” in evolution Genetic Variation and Evolution • Evolution: changes through time 1. Species accumulate difference 2. Descendants differ from their ancestors 3. New species arise from existing ones Evidence of Change • We know that fossils are the remains of once living organisms (animals or plants). • Scientists have organized these remains and labeled it as the fossil record. This organizes organisms based on their similarities and or age groups. A Brief History of Evolution Charles Darwin was born on February 12, 1809 in Shrewsbury, England. From 1831 to 1836 Darwin served as naturalist aboard the H.M.S. Beagle on a British science expedition around the world. He observed much variation in related or similar species of plants and animals that were geographically isolated from each other. These observations were the basis for his ideas. Galapagos Iguanas Giant Tortoises The giant tortoise is a unique animal found only in the Galápagos Islands. There are only about 200 tortoises remaining on these islands. Darwin’s Finches • Most studied. • Each island had its own distinct species. • Beaks differed in size and shape. On the Origin of Species by Means of Natural Selection. • Published in 1859 • Describes Darwin’s observations and • Evidence he collected • To formulate the Theory of Evolution http://spencer.lib.ku.edu/exhibits/darwin/or A Brief History of Evolution Darwin presumed that populations of individuals changed over time, and, in 1844, he developed the concept of the driving force for evolution. It wasn’t until many years later that he published his idea. “I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.” —Charles Darwin from "The Origin of Species“, 1859 Natural selection: mechanism of evolutionary change Natural selection: proposed by Darwin; the process by which organisms that are better adapted to their environment survive and reproduce more successfully than less well adapted organisms do. • individuals have specific inherited characteristics • they produce more surviving offspring • the population includes more individuals with these specific characteristics • the population evolves and is better adapted to its present environment Natural Selection Observation 1: Organisms generally have more offspring than can survive to adulthood. Observation 2: Offspring are not identical. There is variation in their appearance, size, and other characteristics. Natural Selection Inference: Those organisms that are better adapted to their environment have a greater likelihood of surviving to adulthood and passing these characteristics on to their offspring. Survival of the “fittest.” Survival of the “fittest.” Darwin’s theory for how long necks evolved in giraffes Sources of variation Selection • Natural selection: environmental conditions determine which individuals in a population produce the most offspring • 3 conditions for natural selection to occur – Variation must exist among individuals in a population – Variation among individuals must result in differences in the number of offspring surviving – Variation must be genetically inherited Forming a New Species • Drastic changes can form a new species Ex. Weather changes, separation from the population Speciation is the formation of the a new population.