A D B E C F G Charles Darwin Natural Selection Charles Darwin (1809-1882) • 5 year voyage around the world on the HMS Beagle as the ships naturalist. • Observations - Great diversity of organisms - Organisms well suited to environment - Different types of organisms in different parts of the world - Similar organisms with different characteristics EX: Galapagos Island Examples Tortoises Different shaped shells and necks that adapt them to their island habitat Finches Different type of beak’s that adapt a bird to its food source Natural selection was Darwin’s explanation of how evolution occurs. The mechanism of how organisms chanced over time. • Organisms adapt to their environment, structural or functional changes occur from one group of descendants to another • Descended from a common ancestor Darwin’s finches Common Ancestor A shared link between living and extinct species Living organisms share a common ancestor, the more alike organisms are the nearer the common ancestor the more different organisms are the further back in geological time the common ancestor Descent with Modification Each living species has descended, with changes from other species over time Artificial selection- Humans have been doing this for a thousand years with domesticated species • • • • • • His theory included the following: Variation: Over-production: Struggle for existence: Survival of the fittest: Advantageous characteristics past on to offspring: • Gradual change: • Read Cambridge pages 129, explain each • Look at pg 130 at the example of natural selection in cacti EX: Beetles • • • • • • • • • • • • Variation da Brown and green coloration Over-production: Many produced Struggle for existence: Avoiding been eaten Survival of the fittest: Brown beetles are better suited to environment Advantageous characteristics past on to offspring: Brown beetles survive, reproduce pass on genes for brown color Gradual change: Over time population changes to mainly brown beetles Descent with Modification • We’ve defined evolution as descent with modification from a common ancestor • Evolution only occurs when there is a change in gene frequency within a population over time. • Beetle example: genes for the brown color become more frequent Natural selection- selects among whatever variations exist in the population. The result is evolution. Mutations are random in the DNA sequences that lead to these variations Evolution of Populations • A Gene Pool consists of all genes, including all alleles that are present • Allele Frequency of an allele is the number of times that the allele occurs in the gene pool • The relative frequency has nothing to do whether the allele is dominant or recessive. Allele frequencies measure how common certain alleles are in a gene pool Source of Genetic Variation • Mutations are any change in a sequence of DNA occur because of mistakes in replication or environmental factors. Can form a new allele • Recombination occurs during production of gametes (meiosis) during sexual reproduction, it is enhanced by crossing over. • Gene shuffling does not change the relative frequency of alleles in a population. Normal Distribution • Highest frequency of phenotypes is around the mean value • Extreme phenotypes are not favored • Creates a bell-shaped curve Microevolution • Observable change in allele frequency over time within a population • Small scale • Natural selection changes a trait in that population Directional Selection • When individuals on one end of the curve have higher fitness than individuals in the middle or at the other end directional selection takes place • Ex: bacteria Stabilizing Selection • When individuals near the center of the curve have higher fitness than individuals at either end of the curve stabilizing selection takes place. • Ex: Gall fly Disruptive Selection • When individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle, disruptive selection occurs. • EX: Lazuli buntings Gene Flow • Gene flow is the process in which new alleles are added to the gene pool through an outside source • Genes move from one population to another, creating genetic diversity • For example- Migration Genetic Drift • In small populations an allele can become more or less common simply by chance. Overtime, a series of chance occurrences of this type can cause an allele to become common in a population (Just lucky or unlucky) • Commonly occurs when a small group of individuals colonizes a habitat. • Decrease in Genetic diversity Bottleneck Effect • When genetic drift reduces a population • A destructive event leaves only a few survivors • Ex: Holocaust Q. What happens to the genetic diversity in the population? Founder Effect • Small number of individuals colonize a new area • Gene pool can be different from original population. Ex: Amish Sexual Selection • Females are choosy about mates • Certain traits that the males have will increase mating success • Ex: Peacocks showy tail, bigger the tail the healthier the male Reproductive Isolation • Different populations can no longer mate together successfully • Can not physically mate • Offspring that are produced do not survive Ex: Fruit Flies, pheromones Speciation • Speciation is the process in which new species are formed. • Sometimes populations are disrupted to the point where they can no longer mate. This is referred to as reproductive isolation so forming different species • Extinction • Elimination of a species from earth • • • • • • Punctuated Equilibrium Adaptive radiation Gradulism Convergent evolution Divergent evolution Coevolution Convergent Evolution Unrelated species evolve similar traits due to their similar environments Ex: Wings of birds and insects Caudal fin of sharks and dolphins Hardy-Weinberg principle • Scientists find it easier to understand evolution by looking at a hypothetical situation where evolution does not occur. • The populations alleles remain constant (at equilibrium) from generation to generation • Although the situation is unattainable it still provides scientists with accurate information about what drives evolution. 5 Conditions of the Hardy-Weinberg Principle • Random Mating - All members of the population must have equal opportunity to produce offspring • Large Population - there is less effect of genetic drift on large populations • No Movement into or out of the Population- there can be no additional alleles in the population • No Mutations - the DNA must remain consistent • No Natural Selection - all genotypes must have equal opportunity to reproduce.