Evolution Microevolution Speciation Macroevolution EVOLUTION n Evolution refers

Evolution Microevolution Speciation Macroevolution

EVOLUTION n Evolution refers to the processes that have transformed life on Earth from its earliest forms to the vast diversity that characterizes it today.

Views Before Darwin n n The Earth is only a few thousands of years old and a Creator made all the unchanging forms of life found on the planet. Lamarck (1744 -1829) argued that individuals’ traits became more or less prominent due to “use and disuse”.

Lamarck’s Ideas of “Use and Disuse” n n Prominent features are passed on to offspring. This was called “the inheritance of acquired traits. ” His ideas were later proven incorrect by Charles Darwin.

Charles Darwin n n His work, “The Origin of Species, ” in 1859 changed the course of biology and explained a convincing case for evolution. He argued that organisms have changed from earlier forms and proposed the mechanism of natural selection to explain how it occurs.

Natural Selection n n A population of organisms can change over time as a result of individuals with certain traits leaving more offspring than other individuals. Adaptations are those inherited characteristics that enhance an organism’s ability to survive and reproduce in a particular environment.

Darwin’s Influences n n Hutton & Lyell’s work on geological gradualism- the fact that the Earth is constantly changing. Continental drift- the continents are not fixed but drifting on the Earth’s mantle.

Darwin’s Influences n n Malthus’s influencial essay on human population. Artificial Selection

Natural Selection’s Key Ideas n n n All individuals in a population are different from each other and thus reproduce unequally. Diversity is key to evolution. There needs to be variation!!! Natural selection is situational- occurs as organisms interact with their specific environment. Organisms with the best adaptations will survive and reproduce the best. These organisms will pass on their adaptations to their offspring.

Story of the Peppered Moth n n During industrial revolution, soot from factories covered oak trees, turning them dirty and dark. The population of light colored moths decreased and the dark colored moths flourished.

Evidences of Evolution 1. Biogeography- the geographical distribution of organisms. 2. Comparative Anatomy • • Homologous structurescharacteristics resulting from common ancestry. Vestigal organs- structures that have little importance for organisms but are historical remnants of evolutionary ancestors.

Evidences of Evolution 3. Molecular Biology Comparing differences in the amino acid sequence of important proteins such as Cytochrome c and Hemoglobin. 4. Fossil Record Preserved remnants or impressions left by organisms that lived in the past.

Evidences of Evolution 5. Comparative Embryology As vertebrate organisms develop as embryos, distinctive characteristics of their class appear.

Population Genetics n n n Individuals are selected but do not evolve. It is populations that evolve! Population genetics is the study of how populations evolve. It is an integration of Darwinian evolution and Mendelian genetics.

Modern Synthesis n Integration of paleontology, taxonomy, biogeography, population genetics, etc. into a comprehensive theory of evolution.

Hardy-Weinberg Equilibrium n n n An ideal yet unrealistic case where the gene frequencies in a population remain equal. However, in nature, this never occurs! Evolution occurs when allele frequencies change.

Hardy-Weinberg Equilibrium 5 “Musts” for H-W Equilibrium: 1. Breeding population must be large. 2. Mating is random. 3. There is no mutation of the alleles. 4. No immigration or emigration. 5. There is no selection.

Hardy-Weinberg Equation n n All the genes in a population is called the gene pool. H-W Equation: p 2 + 2 pq + q 2 = 1 (p + q = 1)

Causes of Microevolution n n Genetic Drift- changes in gene pool due to chance. Bottleneck Effect- random disasters that cause small surviving population that may differ from original population.

Causes of Microevolution n n Gene Flow- exchange of genetic information due to migration. Mutation- changes in organisms’ DNA. Nonrandom Mating- inbreeding or selective mating. Natural Selection

Fitness n n The “fitness” of an organism is a measure of how much it contributes to the gene pool in the next generation. The relative fitness of a gene is a measure of how well a genotype is passed on to the next generation relative to alternative genotypes on the same locus.

Effects of Selection n 1. 2. 3. Natural selection can affect the frequency of a heritable trait in one of three ways. Stabilizing selection Directional selection Diversifying selection

Sexual Dimorphism n n Strong selection can lead to distinct secondary sexual characteristics between males and females. Example: Story of Asian Jungle Fowl