Chapters 15, 16, and 17 Evolution
The Theory of Evolution Theory– well-tested explanation that unifies a broad range of observations Evolution – change in a kind of organism over time; process by which modern organisms have descended from ancient organisms Can theories change over time? Are theories supported scientifically?
Darwin studied: • Diversity – he found a wide range of living things well adapted to their environment • Fossils– he was curious as to why some were extinct Ground Sloth Fossil
Galapagos Islands Volcanic islands off the west coast of South America Unique species found nowhere else in the world How did this happen?
Darwin Returns Home After Darwin returned home, he studied his notes and specimens He struggled with his observations and how they conflicted with his religion He finally published On the Origin of Species, a book which outlined his theories of natural selection and evolution over time
Darwin’s Influences: James Hutton and Charles Lyell – Geologists whose theories suggested that Earth was extremely old and was always changing slowly over time. Darwin proposed that living things were not fixed in one form, but also changed slowly over time.
Darwin’s Influences: • Jean-BaptisteLamark – proposed the theory of acquired characteristics • Use or disuse…some traits were passed down to help survival of offspring • False theory
Darwin’s Influences Thomas Malthus – an English economist who studied human population growth He believed that if humans became overpopulated, they would struggle to survive without sufficient resources Darwin applied this to animals and plants and believed it was the driving force for evolution.
Darwin studied variation Darwin did not know about genes, but did observe traits being passed on Artificial selection – when humans choose which traits are to be passed on in animals and plants by selective breeding Examples: Breeds of dogs, pidgeons, cows, corn, Brassicaoleraceae
Darwin proposed Natural Selection The idea that there is a struggle for survival…needto find food, mates, run away, hide, or protect themselves Darwin proposed that some individuals were betteradaptedfor their environment Adaptation - any inherited characteristic that increases an organism’s chance of survival “SURVIVAL of the FITTEST”
Descent with Modification Darwin proposed Descent with Modification Living things changed over long periods of time due to natural selection He believed that living things evolved from a “common ancestor” “Tree of life” links all living things
Evidence of Evolution: The fossil record
Evidence of Evolution • Geographic distribution of living things – different animals on different continents looking similar (marsupial wolf and grey wolf) • Animals that are not closely related have similar adaptations
Evidence of Evolution Homologous Structures – structures that have different mature forms but develop from the same embryonic tissues. Vestigial organs remnants of legs in skinks, appendix in humans…
Evidence of Evolution Similarities in Embryology
Pattern of Evolution Coevolution: the change in two or more species in close association with each other Ex: Plants and their pollinators
Patterns of Evolution Cont’d • Convergent Evolution • Organisms appear similar, but are not related • The environment selects similar phenotypes • Ex: streamlined body of dolphins and sharks
Patterns of Evolution Cont’d • Divergent Evolution • Two or more related species become more and more dissimilar • Can result in new species • Response to differing habitats • Adaptive radiation: many related species evolve from a single ancestral species
Chapter 16 – Evolution of Populations Evolution in genetic terms – any change in the relative frequency of alleles in a population. Gene pool – all genes (T, t) present in a population Relative frequency – number of times one allele appears compared to all alleles in the gene pool. (Example: B = 40%, b = 60%) The population is evolving if the frequency changes
Gene Pool allele for brown fur allele for black fur
Sources of Genetic Variation: Mutations – a change in the sequence of DNA. Caused by chemicals, radiation, or just randomly. Can be harmful, helpful, or have no effect. Gene shuffling – genes are recombined during the formation of gametes for sexual reproduction. Does not change gene frequencies on its own. How many genes control one trait?
Single Gene and Polygenic Traits If a trait is controlled by one gene it is called a single-gene trait. Single-gene traits result in only two phenotypes. Example: Tall or Short Polygenic traits result in a range of phenotypes. Example: height of a human being.
Polygenic traits continued… Directional Selection
Polygenic traits continued… Stabilizing selection (Example: Birth weight)
Polygenic traits continued… Disruptive selection Example: Beak Size
Genetic Drift Genetic drift is a random change in gene frequency. Common in small populations Founder effect – a small group migrates away from the original group and has a unique gene pool Examples: Galapagos, Hawaii..
Hardy-Weinberg principle If a population does not evolve, it is in genetic equilibrium. It must: 1. Have random mating 2. Consist of a large population 3. No members move in or out of the group 4. Have no mutations 5. No natural selection occurs Example? Coelacanth?
Speciation • Species – a group of organisms that can breed with one another and have fertile offspring • Speciation – formation of a new species due to natural selection or chance events
Isolating Mechanisms • In order for new species to evolve, groups of organisms must be separated or isolated. • If the two groups change enough, and can no longer breed and create fertile offspring, then new species were formed.
Causes of reproductive isolation - Geographicalisolation – Groups are physically separated. Ecologicalisolation- Groups occupy different habitats. Temporalisolation- reproduce at different times of the day. Behavioralisolation- no attraction. Mechanicalisolation- structural differences. Reproductivefailure- no fertile offspring.
17-2 Earth’s Early History and 17-4 Patterns of Evolution Earth is about 4.6 billion years old Earth’s early atmosphere probably contained: Hydrogen cyanide Carbon dioxide Carbon monoxide Nitrogen Hydrogen sulfide Water
Where did organic compounds come from? 1950s – Stanley Miller and Harold Urey designed experiments that showed organic compounds could be formed from elements in Earth’s early atmosphere if an electric current was introduced Lightning could provide the electric current Amino acids, cytosine, and uracil could be formed in these experiments.
Miller/Urey’s experiment Mixture of gases simulating atmospheres of early Earth Spark simulating lightning storms Cold water cools chamber, causing droplets to form Liquid containing amino acids and other organic compounds
Organic molecules to cells? Organic molecules can form tiny bubbles called proteinoid microspheres, almost like oil in water RNA may have been the first hereditary material, as it can self-replicate and act as catalysts. These components may have been the first primitive cells…but the exact origin of life is a MYSTERY!
Early Bacteria created Oxygen • Cyanobacteria (blue green algae) were probably the first living things to manufacture oxygen • Oxygen changed the atmosphere, turned the sky blue, and allowed organisms to respire aerobically (more efficient)
Endosymbiotic Theory Eukaryotic cells may have formed when larger cells engulfed smaller prokaryotes Mitochondria and chloroplasts may have been free-floating bacteria Evidence: They have DNA and ribosomes similar to bacteria and reproduce by binary fission The ability to respire aerobically and the ability to reproduce sexually increased diversity and influenced evolution
Other Topics: Fossils and ancient life Index fossils Radioactive dating Geologic time scale Evolution of multicellular life Mass extinctions
Patterns of Evolution Macroevolution – large scale evolutionary patterns and processes over long periods of time Extinction Adaptive Radiation Convergent Evolution Coevolution Punctuated Equilibrium Changes in developmental genes
Extinction When a species no longer exists on earth Most extinctions were natural until recent times Can be gradual for individuals or can be catastrophic mass extinctions that affect multiple life forms Scientists believe an asteroid impact caused a mass extinction event in the Cretaceous
Adaptive Radiation When a single species or small group of species evolve into many diverse forms over time. Examples: Mammals evolved, finches evolved
Convergent evolution • When unrelated organisms that live in similar environments develop similar adaptations to survive
Coevolution • The process by which two species evolve in response to changes in each other over time