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. Figure 22.4 Strata of sedimentary rock at the Grand Canyon Early Evolutionist • Jean-Baptiste Lamarck (1809) • Recognized that species change over time • Idea: Inheritance of Acquired Traits • Think about genes: Can experience change genes to fit? 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. 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 • Variation in traits; Some traits give individuals an advantage - make them better competitors. • Members of a species compete with each other for resources like food and space. • “Struggle for existence” 2. Survival of the Fittest • Organism’s ability to survive in it’s environment called it’s fitness • Greater fitness means more reproductive success! – If trait a greater fitness, call it an adaptation – If trait is harmful, a less fitness Peppered Moths Which variation is more fit? 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. Descent with modification 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. Descent from common ancestors Kingdoms Eubacteria Archaebacteria Protista Plantae Fungi Animalia Comparative Anatomy • Morphologically similar structures that perform different functions are called homologous structures. • Supports evolutionary relationship. 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) 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! What can we do with Biochemical Similarities? How old is it really? • Absolute dating: • For rocks, look at ratios of different isotopes present; these vary over time. • When there are remains of organic material (carbon) in a fossil, we can use carbon dating to approximate age objectively Carbon Dating • 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 60,000 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 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. 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. Evolution of the Horse •Track the changes in foot and leg structure as well as teeth. •Relate to environment. Adaptive radiation AKA Divergent Evolution: one ancestor produces many new forms Effects of Natural Selection Changing Allele Frequencies without Natural Selection • Gene flow – individuals join or leave the population • Founder Effect – a few individuals start a new population. • Genetic Drift – random events mean only a few individuals reproduce. Big problem in small populations. Evolution of Organisms • All new inheritable physical traits in an organism represent changes in that organism’s genetics: mutations • Darwin did not understand genetics and so could not explain how traits were passed down through generations. • We can apply genetics to evolutionary theory. So how are new species created? • Organisms must become reproductively isolated. – Will mate only with others of their own kind. – If mating with others does occur, offspring are not fertile. • Requires isolating gene pools. New species from geographic separation and separate evolution New species from a mutation in individual that spreads within existing population Geographic Isolation Reproductive Isolation may also be… • Behavioral – sing the right song, dance the right dance • Temporal – time of year or day • Mechanical – the parts don’t fit • Biochemical – sperm can’t penetrate egg • Chromosomal – chromosome numbers don’t match How fast does evolution work?