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What is this Evolution stuff? EVER-CHANGING POPULATIONS Evolution: Change in allele frequencies in a population’s gene pool over time. Evolution does not occur in individuals… but in populations. Population: Interbreeding group of individuals (one species) in a given geographic area Gene pool: The collection of genes (alleles) of a population Change in base sequence… Heritable (receivable) change in a gene… →Gives rise to new genes → Can be harmful → May be beneficial Mutation: Gene flow: Genes being added (immigration) or taken away (emigration) from a gene pool The Voyages of Charles Darwin The Galapagos Islands are about 525 miles from South America, at the equator. Natural selection: How an env. favors or disfavors certain phenotypes: The fittest survive and reproduce. Genes of less fit individuals are lost. Natural Selection: 4 Principles 1. Overproduction of offspring Most “fit” will survive Inc. competition for resources Natural Selection: 4 Principles 2. Variation Traits (phenotypes) differ Can affect ability to find / utilize food, H2O, shelter, O2, to reproduce, etc. Natural Selection: 4 Principles 3. Adaptation Leads to h in freq. of particular structure, physiological process, or behavior – allowing org. to survive /reproduce better. Fitness used to describe reproductive success Natural Selection: 4 Principles 4. Descent with Modification Environment Changes – Nat. Sel. yields pops. w/new phenotypes to adapt New pops. live differently from ancestors Better adapted than it’s ancestors? With its sheer strength and deadly, bacteria-ridden saliva, the Komodo dragon is the top predator in its range. More about the Komodo… Komodo dragons have thrived in the harsh climate of Indonesia's Lesser Sunda Islands for millions of years, although amazingly, their existence was unknown to humans until about 100 years ago. Reaching 10 feet (3 meters) in length and more than 300 pounds (136 kilograms), Komodo dragons are the heaviest lizards on Earth. They have long, flat heads with rounded snouts, scaly skin, bowed legs, and huge, muscular tails. As the dominant predators on the handful of islands they inhabit, they will eat almost anything, including carrion, deer, pigs, smaller dragons, and even large water buffalo and humans. When hunting, Komodo dragons rely on camouflage and patience, lying in wait for passing prey. When a victim ambles by, the dragon springs, using its powerful legs, sharp claws and serrated, shark-like teeth to eviscerate its prey. Animals that escape the jaws of a Komodo will only feel lucky briefly. Dragon saliva teems with over 50 strains of bacteria, and within 24 hours, the stricken creature usually dies of blood poisoning. Dragons calmly follow an escapee for miles as the bacteria takes effect, using their keen sense of smell to hone in on the corpse. A dragon can eat a whopping 80 percent of its body weight in a single feeding. Natural Selection: 4 Principles (review) Overproduction of offspring Variation Adaptation Descent with modification Types of Natural Selection Stabilizing Selection Env. will eliminate individuals at extremes of population. Example: small babies-less healthy large babies-trouble being born avg. babies – more fitness Giraffes: Long necks are better for getting a mate, short necks are better for drinking water. Medium-sized necks have been selected for. Stabilizing Selection: Types of Natural Selection Stabilizing Selection Disruptive Selection Environment favors individuals at extremes – not intermediates Can split population into subgroups Example: birds live in area where medium-size seeds are less common – birds with large/small beaks eating large/small seeds are more fit Disruptive Selection: Types of Natural Selection Stabilizing Selection Disruptive Selection Directional Selection environment favors individuals at one extreme Example Lighter colored moths more easily seen, birds eat them more freq. Directional Selection: Types of Natural Selection Stabilizing Directional (review) Disruptive Species: group of individuals that share some features and can interbreed Speciation: Change in a species > Can be very slow, or relatively rapid. What causes Speciation? Geographic barriers like rivers and mountains What causes Speciation? Reproductive barriers – like different anatomy or incompatible gametes What causes Speciation? Temporal barriers – reproduce at different times What causes Speciation? Behavioral barriers: blocked by courtship rituals & other habits Three male king penguins follow a female in a courtship ritual. What causes Speciation? Reproductive Barriers Geographic Barriers Temporal Barriers Behavioral Barriers (review) Evolution ENSI Lesson on Human Evolution - Hominoid Chromosomes Patterns of Evolution Macroevolution large scale changes over long periods of time. Some important patterns … Mass extinctions Large numbers of species died out Typically due to habitat change that was too rapid to adapt to. Mass extinctions Large numbers of species died out Website Gradual extinction Cause: other organisms, climate change, disasters Gradual ext. and speciation occur at approx. same slow rate Thylacine (Tasmanian Wolf) A carnivorous marsupial. The last one died in a zoo in 1933. Adaptive radiation (divergent ev.) A species changes into many different forms Convergent evolution Unrelated organisms evolve similarities (analogous structures) when adapting to similar environments; ex: shark, seal, dolphin, fish = streamlined bodies, fins for movement Coevolution Two species evolve in response to changes in each other ex: certain flowers attract certain insects to pollinate Tangle-veined fly (Prosoeca ganglbaueri) visits a small flowering herb called the mountain drumstick (Zaluzianskya microsiphon) in the Drakensberg Mountains of southern Africa. Coevolution Island of Mauritius Humans & their livestock inhabited island in 1581 Last Dodo seen in 1681 Coevolution Calvaria Tree Only about 15 trees left on island, each just over 300 years old. Dodo would eat seeds. Only partially digested seeds would ever germinate… Homologous Structures Similar body structures inherited from common ancestry Examples… Homologous Structures Homologous Structures Gradualism Evolution proceeding in small, gradual but continuous steps Punctuated equilibrium Long periods of stable evolution suddenly have periods of rapid change show in fossil record MiniQuiz Warm-up 1. The forelimb of a man, a cow, a horse, a whale, and a bird have the same bone structure. Are these structures known as A. analogous? B. homologous? C. vestigial? MiniQuiz Warm-up 2. One type of bird does not understand the courtship ritual of another type bird. What type barrier is this? A. Temporal B. Reproductive C. Behavioral D. Geographic MiniQuiz Warm-up 3. The size of horses has gotten larger and larger over time. What type example of speciation is this? A. Stabilizing B. Disruptive C. Directional Phylogeny Descent with modification: Evolutionary tree of elephant family, based on fossil evidence) The evolutionary history of a species or a group of species over geologic time Sequences Reflect Relationships After working with sequences for a while, one develops an intuitive understanding that for a given gene, closely related organisms have similar sequences and more distantly related organisms have more dissimilar sequences. These differences can be quantified. Given a set of gene sequences, it should be possible to reconstruct the evolutionary relationships among genes and among organisms. Human Evolution Interactive (click here) Human Evolution Interactive (click here) Classifying by ancestry Phylogenetic trees or Cladograms (a “clade” is shown in blue) Classifying by ancestry Phylogenetic trees or Cladograms