Natural Selection & Evolution I. Natural Selection & Charles Darwin Due to earth’s long history; life is thought to have evolved over time Charles Darwin (1819-1882) an English scientist considered the founder of the evolutionary theory Darwin studied many forms of life through the voyage of the Beagle Galapagos Islands was where Darwin studied a majority of the organism Darwin's many observations led him to the idea that species slowly change over time (Gradualism) Darwin's comparison of the animals of South America and the Galapagos Islands caused him to conclude that adaptation to the environment can cause diversification, including origin of new species The Galapagos Islands: Volcanic islands off the South American coast Island species varied from the mainland species, and from island-toisland Each island had either long or short necked tortoises depending on the island's vegetation The Galapagos Islands: Finches on the Galapagos Islands resembled a mainland finch, but there were more types Bill shapes are adaptations to different means of gathering food. Galapagos finch species varied by nesting site, beak size, and eating habits Darwin's Theory of Evolution: An adaptation is a trait that helps an organism be more suited to its environment Darwin decided adaptations develop over time Natural selection was proposed by both Alfred Russell Wallace and Darwin as a driving mechanism of evolution Natural Selection: Natural Selection – a mechanism for change in a population where favorable conditions for a particular environment which help organisms, survive, reproduce and pass on these variations. This is also known as “Survival of the Fittest” There is a variation in Traits. Green beetles tend to get eaten more often therefore lessen their chances to The Brown reproduce. Trait is an advantage therefore allows more brown beetles to be produced Artificial Selection - a technique in which a breeder selects the particular traits Pigeon breeding experiments helped him to further study his theory of evolution This was an example of Artificial Selection Adaptations: Mimicry – structural adaptation that provides protection. Allows a harmless species to resemble a harmful species. This caterpillar protects itself by mimicking a snake Adaptations: Camouflage – structural adaptation that enables an organism to blend in with it’s surroundings Katydids camouflage into a variety of environments Adaptations: Structural adaptations can occur over many generations Physiological adaptations can occur very rapidly (organisms adjusting to the changes of environment) Eg: tanning of skin when exposed o sun/ formation of callouses on hands/ change color of coat because of temperature Evidence of Evolution Fossils show changes which have occurred over time: 1. Homologous Structure – modified structure similar in structure and function. (PAP p.384/ p.401) 2. Analagous Structure – similar in function different in structure (Insect wings/Birds) 3. Vestigial Structure – structure which was once used in an ancestral organism, but looses function due to evolution. (mole eyes/ Whale pelvic bones/ ostrich wings) Bell Ringer 2: 1. Define Phenotype. 2. What provides evidence for evolution? 3. What is an adaptation? II. Mechanisms of Evolution Phenotypes may determine the success or failure of an organism If the phenotype is poorly adapted to it’s environment the organism my not survive, therefore not reproduce Populations evolve over time and not individuals this is called “Population Genetics” Genetics Determines Evolution: Gene Pool – All the alleles in a populations genes. In other words every form of a trait Allelic Frequency – the % of any specific allele w/in a gene pool Statsis (Genetic Equilibrium) – allele frequency remains the same over generations Populations in genetic equilibrium are not evolving Factors that affects genes can affect equilibrium 1. Mutations [negative, positive] Negative more than likely causes death Positive may be beneficial 2. Genetic Drift – alteration of allelic frequencies by chance events 3. Gene Flow – transfer of alleles from one population to another population through immigration of individuals . This disrupts allele frequency. Trait Variations – differences in Organisms Increases or decreases an organisms chance of survival Inherited and controlled by alleles Allelic frequencies in a populations gene pool will change due to natural selection Bell Ringer 3: 7. How do alleles affect evolution? 8. How can geographic isolation change a populations gene pool? 9. Why is rapid evolution more likely to occur in small populations? 3 Types of Natural Selection that Act on Variation: 1. Stabilizing – natural selection that favors average individuals 3 Types of Natural Selection that Act on Variation: 2. Directional selection – natural selection that favors an extreme form of a trait 3 Types of Natural Selection that Act on Variation: 3. Disruptive selection – individuals w/ either extreme form of a trait The Evolution of Species: Species – organisms that look alike can interbreed to produce fertile offspring Speciation – evolution of a new species, where members of similar populations no longer interbreed to produce fertile offspring Physical Barriers Cause Speciation: Geographic Isolation – a physical barrier divides a population Reproductive Isolation – the inability of organisms to mate and breed fertile offspring Genetic material becomes so different fertilization can not occur Behavior – mating seasons are different These Bowerbirds have different mating seasons and rituals. These 2 factors contribute to Reproductive Isolation Speciation Rates - the time it takes for evolution to occur Different Theories: Gradualism – idea that species originate through a gradual change of adaptations Punctuated Equilibrium – idea that species originate in rapid bursts followed by long period of genetic equilibrium Speciation: Sympatric Speciation: Is the process through which new species evolve from a single ancestral species while inhabiting the same geographic region. Allopatric Speciation: occurs when the same species become vicariant, or isolated from each other. This can be the result of geographical changes such as mountain formation, island formation, or large scale human activities (for example agricultural and civil engineering developments). Patterns of Evolution Adaptive Radiation – ancestral species evolves into an array of species to fit a particular environment. Divergent Evolution – process of adaptive radiation where individuals become a totally new species Convergent Evolution – distant related organisms evolve and share similar traits. Both of the cactus are located in different parts of the world. Their environment is the same, so they have adapted in some of the same ways.