Transcript Evolution
Evolution Historical Viewpoints • Earth and all organisms have always existed in current state. – Creation by higher authority so NO CHANGE possible. • 18th-19th centuries – evidence that earth may be much older than originally thought and may have changed – Fossils! Hutton and Lyell (geologists) • James Hutton (1785) - examined geologic features such as rock layers and erosion – concluded earth very old. • Charles Lyell (1833) - observed current earth processes: floods, erosion, earthquakes, etc., – concluded same geologic processes shaped the earth to current form. Early Evolutionist • Jean-Baptiste Lamarck (1809) • Recognized that species change over time • Idea: Inheritance of Acquired Traits Social Theory Thomas Malthus (1798) • Describes role of competition for limited resources in human societies. • Not everyone will compete successfully. Charles Darwin • English scientist born in 1809 • Gave up medical studies, went to seminary. • 5 years as naturalist on HMS Beagle – Mission: Explore and document South America’s land forms and animals. On the Origin of Species • Published 1859 • Summarized his ideas on causes of speciation • Darwin's On the Origin of Species by Means of Natural Selection, made several points that had major impact on nineteenth-century thought: Darwin and Natural Selection • Force that causes populations to evolve. • Relies on variation in traits (phenotypes) in any population • Based on 3 main principles 1) Competition 2) Survival of the Fittest 3) Descent with Modification 1. Competition • Members of a species compete with each other for resources like food and space. • “Struggle for existence” • Variation in traits; Some traits give individuals an advantage - make them better competitors. 2. Survival of the Fittest • Organism’s ability to survive in it’s environment called it’s fitness • Greater fitness means more reproductive success! • Random variation in traits in a population – If trait a greater fitness, call it an adaptation – If trait is harmful, a less fitness 3. Descent with Modification • Alleles for adaptations are passed on through generations and accumulate in a species’ gene pool over time. • If enough difference, produces a new species. • Ex. Hawaiian Honeycreepers – All Hawaiian honeycreepers have similarities in skeletal and muscle structure that indicate they are closely related. • Each Hawaiian honeycreeper species has a bill specialized for eating certain foods. • all 23 honeycreeper species apparently arose from a single species – competition for food. Principle of Common Descent • All species (living and extinct) have evolved from common ancestors for a very long time. • Overwhelming evidence supports this – details of how species change not always clear. Evidence of Evolution • Comparative Anatomy - Fossil Record • Geographic Distribution • Homologous Structures – Vestigial Organs • Comparative Embryology • Biochemical Fossil Record • Preserved remain of ancient life in rock, ice, tar, etc. • Fossils found in lower levels of rock older than ones above. (relative age) • Extinction! • Very hard for an organism to become a fossil. (see HHMI evolution, lecture 1: 19) How old is it really? • When there are remains of organic material (carbon) in a fossil, we can use carbon dating to approximate age. • Radioactive isotopes decay at a constant rate – Half Life length of time for ½ of an isotope to decay • Ex. Carbon-14 decays to Nitrogen-14 • Half-life = 5,730 years • Carbon 14 can only be used to date fossils less than 50,000 years old! Geographic Distribution/Biogeography • distribution of plants and animals throughout the world • Some fossils found on different continents are nearly identical supporting movement of continents. • major isolated land areas and island groups develop indigenous species: independent evolution Comparative Anatomy • Morphologically similar structures that perform different functions are called homologous structures. • Supports evolutionary relationship. Analogous Structures • Similar function, very different structure – Insect wing and bird wing – Whale fin and fish fin • Develop when organisms face similar pressure from environment: convergent evolution. Evolution of the Horse •Track the changes in foot and leg structure as well as teeth. •Relate to environment. Vestigial Organs • “Degenerated” structures that are of little or no use to an organism. • Examples of vestigial structures include: – parts of pelvic girdle and leg bones of walking ancestors still in some whales and snakes. – blind, cave-dwelling fish that have eyesockets but no eyes. • Still using same body instructions as ancestors. Comparative Embryology • closely related organisms go through similar stages during their embryonic development Biochemical Similarities • All living things use DNA, ATP (energy molecule), similar enzymes, same codons for protein synthesis, same 20 amino acids etc. • Remember, at the cell level we are very close to most other eukaryotic organisms! Evolution of Organisms • All new inheritable physical traits in an organism represent changes in that organism’s genetics. • Darwin did not understand genetics and so could not explain how traits were passed down through generations. • We can apply genetics to evolutionary theory.