Transcript Slide 1
Classify the following: Trout, catfish, frog, snake, whale, human, cardinal, turtle, salamander, shark, dolphin, bat, blue jay, http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html Did you group them by movement? SWIMMERS Trout Catfish Whale Shark dolphin FLIERS cardinal bat blue jay HOP/CRAWL/SLITHER frog turtle snake salamander UPRIGHT Human Or by: FISH trout catfish shark BIRDS blue jay cardinal AMPHIBIANS frog salamander REPTILES snake turtle MAMMALS whale dolphin human bat Evidence for evolution Scientists compare these things to determine the evolutionary relationships among organisms. 1. body structures 2. development before birth 3. DNA sequences 1. SIMILARITIES IN BODY STRUCTURE An organism’s body structure is its basic body plan (ex. How its bones are arranged.) The 5 classes of vertebrates (fish, amphibians, reptiles, birds and mammals) all have a similar body structure: Internal skeleton w/a backbone. HOMOLOGOUS STRUCTURES: similarities in structure inherited from an early common ancestor 2. Similarities in Early Development Scientists can also make inferences about evolutionary relationships by comparing the early (embryonic) development of different organisms. rat chicken turtle 3. Similarities in DNA Scientists infer that the species inherited many of the same genes from a common ancestor. Genes are made of DNA. By comparing the sequence of nitrogen bases in the DNA of different species, scientists can infer how closely related the species are. The more similar the sequences, the more closely related the species are. Because of its appearance, the tiny elephant shrew was once thought to be closely related to mice. DNA analysis shows that they are much more closely related to elephants! Ya never know!! Combining evidence Scientists have combined evidence from fossils, body structures, and early development, and DNA and protein sequences to determine the evolutionary relationships among species. An example of how scientists combined evidence from different sources is shown in the branching tree. A branching tree is a diagram that shows how scientists think different groups of organisms are related. Below image from Prentice Hall Life Science. Most recent species at top of tree Time moves from the past at the bottom to present time at the top to Forks=Where species began to evolve away from their common ancestor Common ancestor at bottom of tree Natural Selection The process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. 4 Parts of natural selection: 1-overproduction 2-competition/struggle to survive 3-variations 4-selection/successful reproduction 1. Overproduction Most species produce far more off spring than can possibly survive Often so many are produced that there are not enough resources for them all. Ex: Sea turtles What would happen if all the young sea turtles lived? Sea turtles lay 100s of eggs—if they all survived, the ocean would be full of turtles. Darwin knew better… 2. Competition Offspring must compete with each other to survive. Competition does not necessarily mean physical fighting. It is usually indirect For example, Some baby turtles May not be able to find enough to eat. Variations Members of a species differ from each other in many of their traits. Any difference in between individuals of the same species is called variation. For example… Some turtles are able to swim faster than others To escape from predators. Remember you don’t have to be faster than the predator, you just have to be faster than the other prey! Selection Over a long period of time, natural selection can lead to evolution. Helpful variations gradually accumulate in a species, while unfavorable ones disappear. For example… A new faster predator moves into the turtles’ habitat. Perhaps a faster breed of shark… The turtles that are able to swim faster would be more likely to escape from the new predator. The faster turtles would be more likely to survive and reproduce. Over time, more turtles in the species would have the “fast-swimmer” trait. Genes What role do genes have in evolution? Variations can occur due to mutations in genes or from the shuffling of alleles during meiosis. Therefore, only traits that are inherited are acted upon by natural selection How are new species formed? A new species might form when a group of individuals remains separated form the rest of its species long enough to evolve different traits. This is called isolation or complete separation. Continental drift Millions of years ago on the super continent Pangaea, organisms could travel from one part of the continent to another. Pangaea gradually split apart over millions of years in a process called continental drift. As this separation happened, species became isolated from one another and began to evolve independently.