Evolution & Natural Selection Cornell Notes EQ: How Does Natural Selection Influence Evolution? Phoenix Union Curriculum Guide Essential Standard 6.2 Analyze how a change in an environmental factor can affect the number and diversity of individuals in a population (natural selection).
What is the theory of Evolution? • Evolution: The process of change over time • Specifically, a change in the frequency of a gene or allele in a population over time • Not from one day to the next • Usually takes thousands, hundreds of thousands and perhaps millions of years
Who is Charles Darwin? • Father of Evolution • Proposed a mechanism or process for evolution, natural selection • Darwin went on a 5 year trip to the Galapagos to study the different beak types of finches. He noticed that the beak of the finch varied based on the food that it ate. • Wrote a book, “Origin of the Species”
What is the difference between Natural and Artificial Selection? • Natural Selection: Organisms that are best adapted to an environment survive and reproduce more than others. • Artificial Selection: Humans change a species by breeding it for certain traits.
What are the four parts of natural selection? • Darwin’s Theory of Natural Selection occurs in four steps: • Overproduction • Variation • Competition • Selection
What is overproduction? • Each species produces more offspring that can survive
What is variation? • Each individual has a unique combination of inherited traits. • Adaptation: an inherited trait that increases an organism’s chances of survival
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 of types of species in an habitat, the more likely at least some will survive • EX: Dinosaurs replaced by mammals
Which community has a better chance of surviving a natural disaster? Community A Community B
Why is Competition important? • Individuals COMPETE for limited resources: • Food, water, space, mates • Natural selection occurs through “Survival of the fittest” • Fitness: the ability to survive and reproduce • Not all individuals survive to adulthood
What is selection? • The individuals with the best traits/ adaptations will survive and have the opportunity to pass on it’s traits to offspring. • Natural selection acts on the phenotype (physical appearance), not the genotype (genetic makeup) • 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)
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.
What are the types of natural selections? • Stabilizing selection- a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait value
Disruptive Selection-a mode of natural selection in which extreme values for a trait are favored over intermediate values
Directional Selection- a mode of natural selection in which a single phenotype is favored, causing the allele frequency to continuously shift in one direction
Peppered Moth A • Which moth will the bird catch? B
What is Descent with Modification? • Darwin proposed that organisms descended from common ancestors • Idea that organisms change with time, diverging from a common form • Caused evolution of new species
What evidence do we have for evolution? • Fossil Record • Homologous Body Structures • Vestigial Organs • Embryology
Fossils show how much, or how little, organisms have changed over time. One of the problems with the fossil record is that it contains gaps.
Homologous Structures- is an example of an organ or bone that appears in different animals. In other words, it's when very different animals have bones that appear very similar in form or function and seem to be related.
Analogous structures are those structures in different species which perform the same function, have similar appearance and structure but are not evolved together; therefore do not share a common ancestor.
Embryology-supports the theory of evolution because scientists have found that the embryos of many different species show similarities, which implies they share a common origin.
Summary Questions • What is evolution? Does evolution happen to an individual or population? • Why is variation or biodiversity good? • What is the difference between Stabilizing and Disruptive selection? • What evidence proves Evolution?
Summary Questions • What is evolution? Does evolution happen to an individual or population? The change in the frequency of a gene or an allele in a population over time. • Why is variation or biodiversity good? The more variation or diversity within a species provides a higher percentage of its survival. • What is the difference between Stabilizing and Disruptive selection? Stabilizing selection is when the genetic diversity within a population decreases. Disruptive is when extreme traits are valued over intermediate traits. • What evidence proves Evolution? Fossils, Homologous, Analogous and Vestigial structures, embryology