Chapter 15 and 16 Evolution Change through time Theory of Evolution of Life • Charles Darwin -A Naturalist who, in 1831, traveled on the “HMS Beagle” for a five year expedition to discover, collect, study, and store biological specimens. • Father of the Theory of Evolution The Galapagos Islands • Darwin observed many islands with great biodiversity. • Animals and plants seemed to be best suited for their own particular climate. • The organisms on the islands were similar to those on the main island but seemed to have adapted to the island climate. • After 22 years of data analysis he formed his Theory of Adaptation and Natural Selection. Adaptation Adaptation: an anatomical, physiological, or behavioral trait that improves an organism’s ability to survive and reproduce. Darwin’s Theory of Natural Selection • 1. Organisms produce more offspring than can survive. • 2. Variations exist within populations • 3. Some variations are more advantageous than others (struggle for existence) • 4. The “fittest” survive and reproduce! Thus the species modifies itself over time. (Natural Selection) Darwin’s Pigeons • Artificial Selection - By breeding pigeons that had a desirable trait, the offspring would carry these same traits. • Natural Selection - Nature selects or chooses which traits in an organism will be passed on to future generations. Adaptations • Populations adapt as the environment changes 1) Mimicry - Structural adaptation that provides protection by enabling it to copy another species. (Monarch and Viceroy) Adaptations 2) Camouflage - Structural adaptation that enables the organism to blend in with its environment. (Peppered Moths) 3) Physiological Adaptations - Bacteria developing a resistance to penicillin. Five Points of Evidence for Evolution 1. Fossil Record - Identifies a path a species followed as it evolved. Five Points of Evidence for Evolution 2.Anatomical Studies A) Homologous structures Similar in structure, but, different in function. B) Analogous structures Body part similar in function but different in structure. Ex. Wings of bird and butterfly 3. Vestigial Organs - Structures that have no function in the organism today but may have been used. Ex. Appendix 4. Embryological development Organisms that develop similarly as embryos have an evolutionary relationship. (Vertebrate embryos- all have tails and gill slits as they develop) 5. Genetic Similarities - DNA and RNA sequences are similar in related organisms. Vestigial Features Similarities in Embryology Mechanisms of Evolution • Occurs when there is a change in the genetic makeup of a population. • Occurs in population over many generations. • Gene pool - All the genes in a population • Allele frequency - Proportion of each allele in a gene pool (SS,Ss, Ss, ss - 3:1 Spotted to black) 3 Ways Genetic Equilibrium Can Change • Genetic equilibrium - Allele frequencies do not change over time (non evolving) • Ways equilibrium change 1) Mutations – Natural or by chance, genetic changes in gene pool; most harmful, some beneficial and are added to gene pool. 2) Genetic Drift - Changes due to chance events (Small populations) Ex. Amish; short arms/legs 3) Gene flow - Movement of genes into or out of a population; causes the gain or loss of genetic info. 3 Types of Natural Selection • Most significant factor in gene pool changes • 1. Stabilizing Selection - Favors the average individuals in a population. (Grass, Spiders) Types of Natural Selection • 2. Directional Selection- Favors one extreme of a trait (woodpeckers with long beaks) Types of Natural Selection • 3.Disruptive Selection - Individuals with either of two extreme traits are favored. (light, dark, and medium colored limpets) Speciation • Formation of a new species from an ancestral form. • This can only occur when interbreeding or the production of fertile offspring is somehow prevented. • Physical barriers - New mountain ranges, canyons, or water barriers create Geographical Isolation. • Reproductive Isolation -Occurs when mutations prevent offspring development, or seasonal mating changes that prevent mating. Speciation • Speciation can occur quickly or slowly. • Gradualism- Species originate through a gradual accumulation of adaptations. • Punctuated Equilibrium - Occurs in rapid bursts with long periods of stability in between. • Adaptive Radiation - An ancestral species evolves into many different species (Divergent Evolution) • Convergent Evolution -Distantly related organisms evolve similar traits. Ex. Whales and Fish Comparing Convergent and Divergent Evolution Divergent Evolution: A process in which the descendants of a single ancestor diversifies into species that each fit different parts of the environment.