There’s a dragon in my garage • by Carl Sagan • "A fire-breathing dragon lives in my garage" "Show me," you say. I lead you to my garage. You look inside and see a ladder, empty paint cans, an old tricycle — but no dragon. "Where’s the dragon?" you ask. "Oh, she’s right here," I reply, waving vaguely. "I neglected to mention that she’s an invisible dragon." You propose spreading flour on the floor of the garage to capture the dragon’s footprints. "Good idea," I say, "but this dragon floats in the air." Then you’ll use an infrared sensor to detect the invisible fire. "Good idea, but the invisible fire is also heatless." You’ll spray-paint the dragon and make her visible. "Good idea, but she’s an incorporeal dragon and the paint won’t stick." And so on. I counter every physical test you propose with a special explanation of why it won’t work. Now, what’s the difference between an invisible, incorporeal, floating dragon who spits heatless fire and no dragon at all?
Observations provide evidence for theories • Observations provided Darwin with information he used to describe his ideas about evolution • The ideas were already there (de Lemarck), but the observations – evidence – were not • Took Darwin more than 20 years after the Beagle voyage for the publication of his theory on natural selection • Scientific Theory: a statement based on observation and experiment • With continued observation and experiment, the theory may become widely accepted • Can be used to explain AND predict natural phenomena • Theories can change as new evidence is discovered
Fossil evidence supports evolution • Darwin collected specimens of fossils on his trip • Noticed that species from the past were very similar to those of Darwin’s time • Extinct Glyptodon ~ C./S. America Armadillo • Geographic information about fossils provides evidence that two species with a common ancestor can develop differently in different locations • Ancestor: early form of an organism from which later forms develop *** “common ancestors” are important to the theory of natural selection and the evidence that supports the theory -ex: comparing modern plants and modern algae to fossils of algae = share a common ancestor
Biological evidence supports evolution • Scientist are still returning to the Galapagos to follow and record evolutionary changes as they are unfolding, further investigating Darwin’s work • Similarities in structure: • Look at physical structures in different adult organisms
Biological Evidence – Similarities in Structure • Vestigial organs: physical structures that were fully developed and functional in an earlier group of organisms, but are reduced and unused in later species • Whales still have a leg bone that is vestigial (whales are mammals that “went back to the water”), snakes have leg-like structures, our tailbone and appendix • Help to see how modern organisms are related to ancestors that had similar structures
Biological Evidence – Similar (homologous) structures with different functions • Different species may share similar structures, which may be used differently • One long bone goes from shoulder to wrist- forelimb (like book: lizard, bat, manatee) • The similarity in structure indicates that these organisms shared a common ancestor • The process of natural selection caused the variations in form and function • The organisms lived in different environments: different pressures • Land, water, terrain, climate, predators, food supply, etc
Biological Evidence – Similarities in Development • As far back as the 1700s scientists were fascinated by the similarities of animals in their early stages of life • As they developed, they became less and less alike • A rabbit does not look like a chicken, but their embryos do (conception fetus)
Genetic evidence supports evolution • DNA: the key to understanding how traits are passed from one generation to the next • The information needed to grow and maintain • Contains a code a cell uses to put together all materials it needs to function property • Bases: A, T, C, G • Gene: a segment of DNA that relates to a specific trait or function of an organism • Scientists can tell how closely organisms are related by comparing the DNA • Clock genes: relates to the function of sleeping and waking • Goes with patterns of behavior • Gene sequence not all that unlike human (see book)