Evolution- “Change Over Time” All of the changes that have occurred in living things since the beginning of life on Earth
Theories of Evolution Darwin vs. Lamarck
Jean-Baptiste LaMarck • French, Early 1800’s Theory of Inheritance of Acquired Characteristics • Two main points…
1. Principle of Use & Disuse: • Most used body structures develop, unused structures waste away • 2. Inheritance of Acquired Characteristics: • Once the structure is modified, the new trait can be inherited (passed to offspring)
Why we don’t believe him… • Experiments: show that changes that occur in an animal’s life are not passed on to its offspring • Genetics:Gregor Mendel discovered that traits are passed down through GENES (which aren’t affected by the outside world in that way)
Charles Darwin“The Father of Evolution” • 1831- sailed on the HMS Beagle to the Galapagos Islands. • Studied many species of finches. • Published book in 1845: • “On the Origin of Species by Natural Selection”
Darwin’s Theory of Evolution(don’t copy all this it’s on your handout) “Natural Selection” “Survival of the Fittest”
Natural Selection • Process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common.
Four main points… • 1. More organisms are produced than can survive…leads to COMPETITION OVER RESOURCES • Ex’s of resources… • Water • Food • Habitat • Mates
2. Individuals within a population vary, and some of these traits are heritable.
3. Some variations are FAVORABLE (increase chances for survival/ reproduction) • Male vs. Female Cardinals • Male color attracts female= reproductive advantage
Better adapted individuals survive and reproduce • These are the individuals that will pass on their genes to the next generation. • This can change the GENE POOL: • Includes all the genes of every reproductive member of a population
What The theory of evolution IS NOT!!! • It does NOT occur in INDIVIDUALS…only populations! • It does NOT happen quickly…the Earth has a Looooooong history! • It does NOT explain how life came to be on Earth, just how it evolved after it was here. • It does NOT have any driving force except the competition for limited resources.
Species… • A group of organisms that are genetically similar enough to produce healthy, fertile offspring.
Darwin’s Finches An example of Adaptive Radiation
Finch Types: Using Darwin’s Theory, explain how all of these different species evolved.
Darwin…one smart guy… “Seeing this gradation & diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”
Phylogenetic Trees • Show evolutionary “relatedness” • Based on fossil record, dna evidence, structural similarity, etc
What common ancestor do all of These organisms share?
Darwin’s Finches…again… What common ancestor do the seed eating and cactus eating finches share? What do each of the finch pictures on here represent? • Which 2 species are more • closely related: • Mangrove Finch and Woodpecker finch • Small ground finch and Bud-eating finch
Good Questions with Good Answers. • How can new species be formed and the old one not go extinct? Wasn’t the whole reason a new species formed was that it had a survival advantage?
Speciation does NOT necessarily cause EXTINCTION! • A NEW SPECIES’ existence just means… • That POPULATION’S GENES have been altered so much that they can no longer mate with members of the original population. • NOW there are TWO SPECIES • Eventually…one may go extinct, but NOT NECESSARY!!!
Darwin’s Finches…p 558 • Illustrate SPECIATION: when a species breaks into two (or more) • The organisms in the two species can no longer… • INTERBREED
What could cause this to happen? • Occupy a new niche/habitat • Geographic barriers/Reproductive Isolation • Reduction of gene flow • Selective Pressure
Geographic Isolation… Sometimes populations are spit In two due to a geographic barrier. This can lead to reproductive isolation. How could this lead to speciation?
Reduction of Gene Flow… If members of a species live far away from each other, they will have a decreased chance of mating. This would create reduced gene flow, but not total isolation. Speciation would probably also require different selective pressures at the two ends. Eventually, this could alter gene frequencies in groups at different ends of the range so much that they would not be able to mate if they were reunited…that’s speciation!
Selective Pressure • A “pressure” from the environment that makes some individuals more likely to survive and reproduce. • Three types… • Disruptive • Directional • Stabilizing
Types of Natural Selection • Stabilizing Selection • Occurs when natural selection works against the 2 extremes of a trait to make the population more uniform.
Stabilizing Selection • Birth weight of babies • Babies that are too big or too small might have less chance of being born healthy.
Natural Selection • Directional Selection • Selects the extreme of 1 trait.
Directional Selection • In a population of plants, flowers with the brightest color might be selected for in order to attract the most pollinators.
Natural Selection • Disruptive Selection • Selects against the mean of the population.
Disruptive Selection • If there are 2 types of seeds to eat for a population of birds, either of 2 different beak shapes (sharp or blunt) might be selected for, but a beak that’s the average of the 2 shapes might not be particularly good at eating either seed, so it would be selected against.
Three important points… • Evolution occurs over MANY generations • Evolution occurs within POPULATIONS (NOT individuals) • Evolution involves genetic changes in a SPECIES • (Members of a species interbreed to produce healthy, fertile offspring)
The process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common. • Evolution • Natural Selection • Adaptations • Genetic Recombination
Consider, for example, a population of shellfish called limpets. The shell color of these limpets ranges from white, to tan, to dark brown. As adults, limpets live attached to rocks. On light-colored rocks, white-shelled limpets have an advantage because their bird predators cannot easily see them. On dark-colored rocks, dark-colored limpets have the advantage because they are camouflaged. On the other hand, birds easily see tan-colored limpets on either the light or dark backgrounds. These tan-colored limpets will be at a selection disadvantage and will most likely become extinct from the population. This type of natural selection is known as: • Stabilizing Selection • Directional Selection • Disruptive Selection
Consider a population of spiders in which the average size is a survival advantage. Predators in the area might easily see and capture spiders that are larger than average. However, small spiders may find it difficult to find food. Therefore, in this environment, average-sized spiders are more likely to survive. This type of natural selection is known as: • Stabilizing Selection • Directional Selection • Disruptive Selection
Imagine a population of woodpeckers pecking holes in trees to feed on the insects living under the bark. Suppose that a species of insect that lives deep in tree tissues invades the trees in a woodpecker population’s territory. Only woodpeckers with long beaks could feed on that insect. Therefore, the long-beaked woodpeckers in the population would have a selective advantage over woodpeckers with very short or average-sized beaks. This type of natural selection is known as: • Stabilizing Selection • Directional Selection • Disruptive Selection
The smallest unit that can evolve is: • A genome • An individual • A community • A population
To predict evolutionary activity, we look at the population’s Gene Pool • Gene pool - all the genes of every reproductive member of a population.
Genetic Equilibrium • Not all populations are in an active state of “natural selection” • GENETIC EQUILIBRIUM • This means that there is no change in the gene pool = no evolution
Genetic Equilibrium • 1.) Population size is large • 2.) No gene flow in the population • No new organisms introducing more alleles • 3.) No mutations • 4.) No environmental factors causing natural selection • No trait is favorable over another • 5.) Random mating must occur
So what factors exist to make a population evolve? • It must NOT be in GENETIC EQUILIBRIUM • Something that knocks the population out of genetic equilibrium is called a MECHANISM OF EVOLUTION
Sources of Genetic Variation • What do you think are some sources of genetic variation? Mutations Natural Selection gene flow genetic drift