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Transcript
Darwin & Natural Selection Theory of Evolution Evolution is the process of change in all forms of life over generations. It suggests that all life has common ancestors. Evolution can be seen in small changes over a (relatively) short period of time or massive changes over an extremely long period of time. Charles Darwin Charles Darwin was an English naturalist who, in the mid 1800s, developed a theory of how evolution works. A naturalist is a person who studies plants and animals by observing them. Darwin went on a 5-year trip around the world on the ship, the HMS Beagle As the ship’s naturalist, he made observations of organisms in South America and the Galapagos Islands •Wrote a book, “Origin of the Species” Darwin’s Finches So what does this mean? Individuals in a population have variations. A variation is a slight difference in an inherited trait of individual members of a species. Variations arise naturally in populations, occurring in offspring as a result of sexual reproduction. Genetic changes can be passes on to future generations. This can lead to totally new species! Natural Selection Natural Selection is the process by which populations of organisms with variations that help them survive in their environments live longer, compete better, and reproduce more than those that do not have the variations. Natural selection explains how populations change as their environments change. Darwin’s Theory of Natural Selection Darwin proposed the theory that evolution happens through a process that he called natural selection This process has four parts: Overproduction Variation Competition Selection 1. Overproduction Each species produces more offspring that can survive 2. Variation Each individual has a unique combination of inherited traits. Adaptation: an inherited trait that increases an organism’s chances of survival What adaptations do you see? What adaptations do you see? Why is Variation Important? Because the environment changes. The more variation within a species, the more likely it will survive. Ex: If everyone is the same, they are all vulnerable to the same environmental changes or diseases The more variation in the types of species in an habitat, the more likely at least some will survive Ex: Dinosaurs replaced by mammals 3. Competition Individuals COMPETE for limited resources: Food, water, space, mates Natural selection occurs through “Survival of the fittest” Fitness: the ability to survive and reproduce Due to limited resources, not all offspring will survive. 4. Selection The individuals with the best traits / adaptations will survive and have the opportunity to pass on it’s traits to their offspring. Ex: When a predator finds its prey, it is due to the prey’s physical characteristics, like color, size, or slow speed, Individuals with traits that are not well suited to their environment either die or leave few offspring. Evolution occurs when good traits build up in a population over many generations and bad traits are eliminated by the death of the individuals. Peppered Moth A Which moth will the bird catch? B Evidence for Evolution: Fossil Record Homologous Body Structures Vestigial Organs Embryology Biochemical Evidence The Fossil Record Fossils: a record of the history of life on Earth Homologous Body Structures Homologous Body Structures: similar anatomy in different types of animals because of common ancestor Vestigial Structures Vestigial Structures are body parts that have lost their original function through evolution and no longer serve a purpose. Embryology the science of the development of embryos from fertilization to birth is called Embryology All vertebrate embryos exhibit pharyngeal pouches at certain stages of their development. These features, which develop into neck and face parts, suggest relatedness. Biochemical Evidence Biochemistry: DNA with more similar sequences suggest species are more closely related Ex: Humans and chimpanzees share more than 98% of identical DNA sequences