Evolution presented by Betsy Sanford 7 th Grade

Evolution presented by Betsy Sanford 7 th Grade Life Science Lost Mountain Middle School

Charles Darwin’s Voyage English naturalist 1831, sailed from England to South America to the Galapagos Islands Observed plants and animals Wondered about, and was amazed at, diversity (variety) of species Began to compare and contrast the different species from one place to the next Collected many specimen

Similarities and Differences Mainland S. America Galapagos Islands cormorants (sea birds) could fly iguanas (lizards) had smaller claws, climbed trees and ate tree leaves cormorants could not fly iguanas had sharp claws, crawled over rocks and ate seaweed

Adaptations Galapagos Islands tortoises on different island had different shell one island had dome-shaped one island had saddle-shaped different birds had different beaks based on what was available on the island to eat insect eaters had sharp beaks seed eaters had strong, wide beaks

Evolution Darwin thought carefully about his data. Darwin consulted other scientists. After 20 years, he made a theory. Evolution means slow gradual change in a species over time. Darwin thought that species changed over time, generation by generation, to be better able to live in an environment.

Natural Selection Survival of the fittest. The best adapted animals will survive to reproduce the next generation. Those that are not adapted to survive will die off. Natural selection is affected by four factors: overproduction, competition, variations, and selection.

Natural Selection Overproduction - Most organisms produce too many offspring. Competition - Survival is limited by food, water, and predators. Variations - Genetic differences and mutations occur in reproduction. Selection - The best adapted will survive to reproduce and pass traits to offspring.

Natural Selection Example: A turtle that can swim faster due to a genetic trait or mutation has a variation that allow it to survive longer than slow turtles who get caught by predators. The faster turtles survive, reproduce, and pass the fast-swimmer trait on to the next generation.

Genetics Heredity Traits are passed from parent to offspring. Remember Punnett squares - genes get shuffled. Genes may also mutate. Geography Isolation provides a limited number of mates. Isolation may occur due to natural disasters hurricanes, earthquakes, continental drift, etc. Eventually, a new species will develop from those who are best suited to survive in the isolated environment.

The Fossil Record Fossils form from dead organisms buried in sediment that hardens into sedimentary rock. Fossils may also be preserved in tar pits, ice, or tree sap (amber). Scientists are now learning to and practicing the extraction of DNA from fossils.

Dating Fossils Relative Dating Using layers of rock in a riverbed to determine age. The most recent layers contain the youngest fossils. Absolute Dating Based on radioactive chemicals found in organisms as they decay. Scientists compare the chemicals in a fossil to elements that they will decay into. Geologic Time Scale Based on absolute dating of fossils, scientists estimate that the earth is 4. 6 billion years old.

Other Evidence for Evolution Homologous structures - similar body arrangement. Example: all vertebrates have a backbone. Early development - similar stages and features during growth. Example: turtles, chickens, and rats all have a tail and tiny gill slits in their throats when they are in the egg. DNA Similarities - comparing nitrogen bases in genes (A, T, C, G sequences). The more alike the sequences, the more related organisms are.

Combining the Evidence Scientist use the combined evidence from fossils, body structures, early development, and DNA and protein sequencing to determine the relationship among species. Macroevolution - the gradual rise of all species from a single organism from the beginning of time (the underlying theory of modern biology). Microevolution - the changes in a species that are observed from generation to generation (day to day, year to year, observable by us).