Download
1 / 42
450 likes | 747 Vues
Evolution = Change Over Time. Theory of Evolution. Describes the slow change in organisms over many generations. Evolution happens by Natural Selection. Theories are central to scientific thinking. Theories are explanations that help make sense of nature are based on evidence
E N D
Theory of Evolution Describes the slow change in organisms over many generations. Evolution happens by Natural Selection.
Theories are central to scientific thinking • Theories are • explanations that help make sense of nature • are based on evidence • allow scientists to make valid predictions • have been tested in many ways
Theories are also • supported, modified, or replaced as new evidence appears • Major theories of science, such as the cell theory, gravitational theory, evolutionary theory, and particle theory, are all big ideas within which scientists test specific hypotheses.
The scientific definition of "theory" should not be confused with the way the term is commonly used to mean a guess or a hunch. In science, a theory means much more and is far more well-founded. The "Theory of Evolution" is an evidence-based, consistent, well-tested explanation of how the history of life proceeded on Earth — not a hunch. Understanding the role of theory in science is essential to scientists and vital to the informed citizen.
Natural Selection Natural Selection – process where individuals that are better adapted to their environment are more likely to survive and reproducethan other members of the same species: 1. Organisms produce more offspring than can survive. 2. Competition for food, space and resources. 3. There are genetic differences (variations) among the species. 4. Individuals with the best traits (adaptations) are most likely to survive, reproduce and pass trait to offspring.
Overproduction + Competition + Variations (genetic differences) + Selection =Natural Selection
Overproduction • Organisms produce more offspring than can survive
Competition • Members of the same species living in the same population must compete for food, space and even mates.
Variations • All life forms vary genetically within a population. Natural selection works upon this genetic variation. • Sources of variation: Mutations and Sexual Reproduction
Selection • The most well adapted (most “fit”) individuals are mostly likely to survive, reproduce and pass traits to offspring.
Sexual Reproduction • Sexual Reproduction results in offspring that are always unique because they receive chromosomes from both parents. Also, during Meiosis some of those genes are mixed up.
Evolution takes time. Evolution can happen in a few generations, but major change often takes long periods of time.
How do new species form? • Geographic Isolation - when a population (group of the same species) remains separated by land or water from other populations long enough to evolve different traits.
“Evolution is like a climb up a ladder of progress; organisms are always getting better.” WRONG!
Misconception:“Evolution is like a climb up a ladder of progress; organisms are always getting better.” Climates change, rivers shift course, new competitors invade—and what was “better” a million years ago, may not be “better” today. What works “better” in one location might not work so well in another. Fitness is linked to environment, not to progress.
Natural Selection does not grant organisms what they “need.”
Adaptation • An Adaptation is a trait that helps an organism survive and reproduce in its environment. Adaptations are the result of an organisms unique genetic code. Over many generations, adaptations in a population of organisms can change in response to a changing environment. • Structural Adaptation - fur color, shape, body covering, claw or tooth size, etc. • Behavioral Adaptations - time or method of feeding, migration, etc. • Physiological Adaptations - body systems that enable the organism to produce special substances (venom, slime, special proteins for digestion, etc.)
Structural Adaptations • A structural adaptation involves some part of an animal's body, such as the size or shape of the teeth, the animal's body covering, or the way the animal moves. • Teeth - since different animals eat different things, they don't all have the same kind of teeth • Body coverings - Hair, scales, spines, and feathers grow from the skin. All of these parts help animals survive in their environments. • Movement - animals find food by moving from place to place
The streamlined shape of these Yellowfin tuna is no accident. A more streamlined shape allows these fish to move through the water faster. During their evolution, natural selection favored the more streamlined tuna.
Protective coloration and protective resemblance • Protective coloration and protective resemblance allow an animal to blend into its environment. Another word for this might be camouflage. Their camouflage makes it hard for enemies to single out individuals.
Mimicry • Mimicry allows one animal to look, sound, or act like another animal to fool predators into thinking it is poisonous or dangerous. • The non-venomous milk snake (right), for example, closely mimics the color pattern of the venomous coral snake. The strategy is a successful one, as some young, inexperienced snake-eating birds instinctively avoid a pattern of alternating red and yellow rings.
Behavior Adaptations • Behavior adaptations include activities that help an animal survive. Behavior adaptations can be learned or instinctive. (a behavior an animal is born with). • Social behavior - some animals live by themselves, while other live in groups. • Behavior for protection - An animal's behavior sometimes helps to protect the animal. For instance the opossum plays dead. A rabbit freezes when it thinks it has been seen.
Migration- is the behavioral adaptation that involves an animal or group of animals moving from one region to another and then back again. Animals migrate for different reasons. • better climate • better food • safe place to live • safe place to raise young • go back to the place they were born.
Hibernation- is a deep sleep in which an animal's body temperature drops to about the temperature of the environment. Body activities, such as heartbeat and breathing are slowed causing the animal to need very little food. The animal lived off of the fat that is stored in it’s body. Animals that hibernate are: • bats • rodents • snakes • amphibians • bears are not true hibernators.
The Ice Fish has an extraordinary adaptation that allows it to survive the extreme Antarctic cold. • It has evolved to have no red blood cells and no hemoglobin, meaning that its blood flows more freely. The oxygen which its muscles need simply dissolves in the blood. • (Image: J Gutt, Alfred Wegener Institute)
Darwin’s Finches Geospiza magnirostris Geospizafortis Geospiza parvula Certhidea olivacea
EVIDENCE • Fossils, especially Transitional Fossils • Radiometric Dating • Homologous Structures • DNA
Fossils – the physical remains or imprint of an organism. archaeopteryx
Radiometric Dating • A technique used to date fossils and rock. Measures the amount of a certain element, such as carbon, that remains compared to the amount that has decayed. Since the rate of decay for each element is constant it is possible to predict the age of the sample.
Radiometric dating allows scientists to project the age of a fossil. • This technique can be used on the fossil itself or on the rocks in which they are found.
Homologous Structures • Scientists look at these physical characteristics to determine how closely related different organisms might be. Similarities suggest the organisms may share a common ancestor.
DNA has become the most important piece of evidence for the Theory of Evolution.
Misconceptions about humans It is important to remember that: • Humans did not evolve from chimpanzees. • Humans and chimpanzees share a common ancestor that was neither chimpanzee nor human. • Humans are not “higher” or “more evolved” than other living lineages. Since our lineages split, humans and chimpanzees have each evolved traits unique to their own lineages.
“I know you miss the Wilsons, Bobby, but they were weak and stupid people—and that’s why we have wolves and other large predators.”
