Darwin vs. Lamarck

Lamarck Darwin

Jean-Baptiste LaMarck French, Early 1800’sFrench, Early 1800’s Theory of Inheritance of Acquired Characteristics Two main points…Two main points…

1. Principle of Use & Disuse: Most used body structures develop, unused structures waste awayMost 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)Once the structure is modified, the new trait can be inherited (passed to offspring)

Explain the picture below as if you were LaMarck…

Why we don’t believe him… Genetics : Gregor Mendel discovered that traits are passed down through GENES (which aren’t affected by the outside world in that way)Genetics : Gregor Mendel discovered that traits are passed down through GENES (which aren’t affected by the outside world in that way) Experiments: show that changes that occur in an animal’s life are not passed on to its offspringExperiments: show that changes that occur in an animal’s life are not passed on to its offspring

Charles Darwin “The Father of Evolution” sailed on the HMS Beagle to the Galapagos Islands sailed on the HMS Beagle to the Galapagos Islands. Studied many species of finches.Studied many species of finches. Published book in 1845:Published book in 1845: “On the Origin of Species by Natural Selection”“On the Origin of Species by Natural Selection”

Darwin’s Theory of Evolution (don’t copy all this it’s on your handout) Darwin’s Theory of Evolution (don’t copy all this it’s on your handout) “Survival of the Fittest” “Natural Selection”

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.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.

Natural Selection

Four main points… 1. More organisms are produced than can survive…leads to COMPETITION OVER RESOURCES1. More organisms are produced than can survive…leads to COMPETITION OVER RESOURCES Ex’s of resources…Ex’s of resources… WaterWater FoodFood HabitatHabitat MatesMates

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 CardinalsMale vs. Female Cardinals Male color attracts female= reproductive advantageMale color attracts female= reproductive advantage

4.Better adapted individuals survive and reproduce These are the individuals that will pass on their genes to the next generation.These are the individuals that will pass on their genes to the next generation. This can change the GENE POOL:This can change the GENE POOL: Includes all the genes of every reproductive member of a populationIncludes 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 occur in INDIVIDUALS…only populations! It does NOT happen quickly…the Earth has a Looooooong history!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 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.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.A group of organisms that are genetically similar enough to produce healthy, fertile offspring.

Darwin’s Finches…p 558 Illustrate SPECIATION: when a species breaks into two (or more)Illustrate SPECIATION: when a species breaks into two (or more) The organisms in the two species can no longer…The organisms in the two species can no longer… INTERBREEDINTERBREED What could cause this to happen?What could cause this to happen? Geographic barriersGeographic barriers Occupy a new niche/habitatOccupy a new niche/habitat Reproductive Isolation-Reproductive Isolation-

Natural selection

What would Darwin say to explain why giraffe’s have such long necks? See pg. 553See pg. 553

Types of Natural Selection Stabilizing SelectionStabilizing Selection Occurs when natural selection works against the 2 extremes of a trait to make the population more uniform.Occurs when natural selection works against the 2 extremes of a trait to make the population more uniform.

Stabilizing Selection

Birth weight of babiesBirth weight of babies Babies that are too big or too small might have less chance of being born healthy.Babies that are too big or too small might have less chance of being born healthy.

Natural Selection Directional SelectionDirectional Selection Selects the extreme of 1 trait.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.In a population of plants, flowers with the brightest color might be selected for in order to attract the most pollinators.

Natural Selection Disruptive SelectionDisruptive Selection Selects against the mean of the population.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.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.

Evolution- “Change Over Time” All of the changes that have occurred in living things since the beginning of life on EarthAll of the changes that have occurred in living things since the beginning of life on Earth

History of the Earth 4.5 bya Earth forms 3.5 bya 1 st PROKARYOTES 2.1 bya 1 st EUKARYOTES

700 million years ago…

Evolution occurs over MANY generationsEvolution occurs over MANY generations Evolution occurs within POPULATIONS (NOT individuals)Evolution occurs within POPULATIONS (NOT individuals) Evolution involves genetic changes in a SPECIESEvolution involves genetic changes in a SPECIES (Members of a species interbreed to produce healthy, fertile offspring)(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. 1.Evolution 2.Natural Selection 3.Adaptations 4.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: 1.Stabilizing Selection 2.Directional Selection 3.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: 1.Stabilizing Selection 2.Directional Selection 3.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: 1.Stabilizing Selection 2.Directional Selection 3.Disruptive Selection

The smallest unit that can evolve is: 1.A genome 2.An individual 3.A community 4.A population

Genetic Equilibrium Not all populations are in an active state of “natural selection”Not all populations are in an active state of “natural selection” GENETIC EQUILIBRIUMGENETIC EQUILIBRIUM This means that there is no change in the gene pool = no evolutionThis means that there is no change in the gene pool = no evolution

Genetic Equilibrium 1.) Population size is large1.) Population size is large 2.) No gene flow in the population2.) No gene flow in the population No new organisms introducing more allelesNo new organisms introducing more alleles 3.) No mutations3.) No mutations 4.) No environmental factors causing natural selection4.) No environmental factors causing natural selection No trait is favorable over anotherNo trait is favorable over another 5.) Random mating must occur5.) Random mating must occur

So what factors exist to make a population evolve? It must NOT be in GENETIC EQUILIBRIUMIt must NOT be in GENETIC EQUILIBRIUM Something that knocks the population out of genetic equilibrium is called aSomething that knocks the population out of genetic equilibrium is called a MECHANISM OF EVOLUTION

Mechanisms of Evolution 1. Natural Selection1. Natural Selection 2. Sexual Selection / Non-random mating2. Sexual Selection / Non-random mating 3. Mutation3. Mutation 4. Gene Flow (Migration)4. Gene Flow (Migration) 5. Genetic Drift- reduces population size5. Genetic Drift- reduces population size Bottleneck effectBottleneck effect Founder effectFounder effect

How does reproduction affect natural selection Discuss with your partner:Discuss with your partner: How would a population that reproduces asexually “evolve” differently than one that reproduces sexually? WHY?How would a population that reproduces asexually “evolve” differently than one that reproduces sexually? WHY?

A note on sexual reproduction … Sexual reproduction can produce many different phenotypesSexual reproduction can produce many different phenotypes Sexual reproduction does NOT change relative frequency of alleles in a populationSexual reproduction does NOT change relative frequency of alleles in a population Think about shuffling a deck of cardsThink about shuffling a deck of cards Shuffling cards gives you different handsShuffling cards gives you different hands It won’t change the number of kings in a deckIt won’t change the number of kings in a deck