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10/7/2015 EVOLUTION 1 CHARLES DARWIN HMS Beagle in port Darwin in 1840 North America Great Britain Europe Asia Africa PACIFIC OCEAN Equator Galápagos Islands Australia Cape of Good Hope Cape Horn 0 0 40 km Tasmania New Zealand 40 miles 2 1 10/7/2015 THE GALAPAGOS ISLANDS Many species that live here are found nowhere else in the world 3 DARWIN’S THEORY OF EVOLUTION Living species are different versions of ancestral species • Published his observation in a book: On the Origin of Species • Suggested that as descendants of a remote ancestor spread into various habitats (over millions and millions of years) they accumulate diverse modifications. • Theory: a widely accepted general idea that is broader in scope than a hypothesis 4 2 10/7/2015 FOSSILS Fossils document the differences and similarities among present and past organisms The fossil record – over millions of years of geological sediment and fossils layered in the order that they appeared in earth’s history 5 FOSSILS OF TRANSITIONAL FORMS Provide evidence for evolution by forming links between ancient and present organisms 6 3 10/7/2015 FOSSILS OF TRANSITIONAL FORMS Provide evidence for evolution by forming links between ancient and present organisms Pelvis Femur Tibia Foot Pakicetus “whale of Pakistan” Rodhocetus Dorudon Living whales (cetaceans) 7 HOMOLOGOUS STRUCTURES Anatomical similarities resulting from common ancestors Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat 8 4 10/7/2015 HOMOLOGOUS STRUCTURES Vestigal structures remnants of features that served an important function in an organism’s ancestor Embryo 2 Embryo 1 Pharyngeal Pouches (gill like structures) Post-anal tail Pseudogenes– retained genes that have lost their function 9 EVOLUTIONARY TREE Shows patterns of descent and uses homologous structures to indicate where specific characteristics have evolved. Lungfishes Branches represent a common ancestor that is Shared by all species to the right of the branch Aniotes Mammals 2 Tetrapod limbs Lizards and snakes 3 Amnion 4 Crocodiles 5 Ostriches 6 Feathers Hawks and other birds Birds Hatch marks show a homologous character shared by all the groups to the right of the mark Tetrapods Amphibians 1 10 5 10/7/2015 GENETIC VARIATION Genetic variation in populations is necessary for evolution to occur • Variation in genotypes that results in different phenotypes • Pleiotropy (1 gene affects many characteristics) allows for lots of variation Mutations and sexual reproduction produce genetic variation in populations 11 EVOLUTION ACTS ON POPULATIONS IT DOES NOT ACT ON INDIVIDUALS 12 6 10/7/2015 GENE POOL All copies of every single allele in all members of a population (Fish tank example) We can measure evolution by documenting changes in the heritable traits of a population over time (Ex: Fish color) POPULATION – a group of individuals of the same species that live in the 13 same area and interbreed. (Galapagos tortoises) EVOLUTION IS A CHANGE IN THE GENE POOL OVER TIME This can happen several ways: 1. Mutations 2. Non‐random mating 3. Genetic drift (chance events) ‐ bottleneck effect ‐ founder effect 4. Gene flow (migration) 5. Natural Selection 14 7 10/7/2015 NATURAL SELECTION Individuals with a certain inherited trait survive better or reproduce more as a result of that trait Natural selection is the ONLY mechanism that leads to ADAPTATION EX: Elephant tusks ADAPTATION – A inherited character that enhances an organisms ability 15 to survive or reproduce in its particular environment SEXUAL SELECTION Certain traits increase an organisms fitness by helping them get mates Male Hercules Beetles fight other males for mates 16 8 10/7/2015 SEXUAL SELECTION Sexual dimorphism results in a “showier” sex (often males) • Female peacocks choose to mate with showy males • “Good genes” hypothesis • Can be risky for males! 17 NATURAL SELECTION Can affect variation in populations in three ways 1. Stabilizing selection – favors intermediate phenotypes and reduces variation in populations 1. 2. Directional selection – favors 1 extreme phenotype (common during environmental change or in migrating populations) 2. 3. Disruptive selection – favors both extreme phenotypes (can result from patchy environments) 3. 18 9 10/7/2015 EVOLUTION OF SUPERBUGS By over‐using anti‐biotics we have increased the numbers of drug‐ resistant bacteria or “superbugs” (Sarcasm) 19 Penicillin was the first antibiotic devoped. It is virtually useless today. BALANCING SELECTION Natural selection can also preserve genetic variation of diploid organisms in a few ways 1. Heterozygote Advantage – selection where heterozygotes have better reproductive success than homozygotes (Ex: Sickle cell anemia) 2. Frequency Dependent – selection that acts against the most common phenotype (Ex: Scale eating fish) 20 10 10/7/2015 SELECTION CAN’T MAKE “PERFECT” ORGANISMS Bummer! Why? 1. Selection can only act on existing traits (no traits on demand) 2. Evolution is limited by historical constraints (traits must be passed) 3. Adaptations are often compromises (peacocks) 4. The future is not predictable (environment can change) Photo courtesy of iflscience.com Tardigrade: lives in damp environments all over the world 21 BUT…BELLA IS PRETTY PERFECT……. ARTIFICAL SELECTION: selective breeding of plants and animals to promote desired traits in offspring Same idea as natural selection, only WE are doing the selecting instead 22 of the environment 11 10/7/2015 REQUIRED VIDEOS Now you know I’m not bluffing about these being on exams! THE FIVE FINGERS OF EVOLUTION See link on the course website: http://www.biosbcc.net/harrer 23 12