Darwin & Natural Selection Theory of Evolution ▪ Evolution: The process of change over time • Specifically, a change in the frequency of a gene in a population over time Evolution is when organisms change over time. Modern organisms descended from ancient ones Charles Darwin ▪ Father of Evolution ▪ Created the theory of natural selection ▪ Darwin made observations of finches in the Galapagos Islands Darwin’s Finches Darwin’s Finches: ◦Are a group of about fifteen species of birds. They belong to the tanager family and are not closely related to true finches. They were first collected by Charles Darwin on the Galápagos Islands. ◦Charles Darwin collected several finch species including the warbler finch, sharp beaked finch, ground finch, small tree finch, large tree finch, common cactus finch, and large ground finch. Darwin’s Finches: ◦Darwin failed to note which islands each finch came from. He left to go back to London and experts informed him that many of the specimens he had thought were different birds were all finches that looked different from one another. ◦This variation helped Darwin arrive at his understanding that the finches and other birds had adapted to the islands and specific environments where they live, leading to the theory that species are not fixed and unchanging. ◦They evolved over time from common ancestors. Artificial Selection ▪ nature provides variation, humans select variations that are useful. ▪ Example - a farmer breeds only his best livestock Natural Selection ▪ The traits that help an organism survive in a particular environment are “selected” in natural selection Natural Selection ▪ Natural Selection: Organisms that are best adapted to an environment survive and reproduce more than others. Survival of the fittest. ▪ Darwin’s Theory of Natural Selection occurs in four steps: • Overproduction • Variation • Competition • Selection 1. Overproduction ▪ Each species produces more offspring that can survive 2. Variation ▪ Each individual has a combination of inherited traits. ▪ Adaptation: an inherited trait that increases an organism’s chances of survival Why is Variation Important? ▪ The more variation within a species, the more likely it will survive • If everyone is the same, they’re all at risk to the same environmental changes/diseases ▪ The more variation of types of species in a habitat, the more likely some will survive • Dinosaurs replaced by mammals 3. Competition ▪ Individuals COMPETE for limited resources: • Food, water, space, ▪ Natural selection occurs through “Survival of the fittest” 4. Selection ▪ The individuals with the best traits / adaptations will survive and pass on traits to their offspring. • Natural selection acts on the phenotype which is the physical appearance. • Ex: When a predator finds its prey, it is due to the prey’s physical characteristics, like color or slow speed, not the alleles (BB, Bb) Descent with Modification ▪ Descent with Modification – Passing traits from parent to offspring and this concept is one of the fundamental ideas from Charles Darwin's theory of evolution. Parents pass traits on to their children in a process known as heredity. The unit of heredity is the gene. Genes are like a blueprint for how a person will be. Your genes combine with your partner's genes and small changes or mutations may occur along the way. Over extended periods of time, evolution takes place! Common Descent ▪ Common Descent All living things are related. They all relate to one single ancestor. Not observable fact. The Fossil Record ▪ Fossil Record: a record of the history of life on Earth Relative Dating ▪ Can determine a fossil’s relative age ▪ Performed by estimating fossil age. Absolute dating ▪ Can determine the absolute age in numbers ▪ Is performed by radioactive dating . Homologous Body Structures ▪ Homologous Body Structures: similar anatomy in different types of animals because of common ancestor Embryology ▪ Embryology: embryos of all vertebrates are very similar early on Summary of Darwin’s Theory 1. Organisms differ; variation is inherited 2. Organisms produce more offspring than survive 3. Organisms compete for resources 4. Organisms with the best traits survive & pass those traits to their children 5. Species alive today are descended with modifications from common ancestors.