Mechanisms for Evolution

Differing Viewpoints… Jean-Baptiste Lamarck Jean-Baptiste Lamarck Evolution occurs through the use and disuse of physical featuresEvolution occurs through the use and disuse of physical features Features will increase by use or decrease by disuseFeatures will increase by use or decrease by disuse These traits are than passed down to their offspringThese traits are than passed down to their offspring

Differing Viewpoints…  Charles Darwin Characteristics among members of a species vary. Characteristics among members of a species vary. Only individuals with the characteristics suited to the environment will survive to reproduce. Only individuals with the characteristics suited to the environment will survive to reproduce. Over time those characteristics will increase in the population. Over time those characteristics will increase in the population.

Lamark vs. Darwin

Natural Selection  Process by which populations change in response to their environments.  Five Requirements: Overpopulation Overpopulation Struggle for Existence (Competition) Struggle for Existence (Competition) Genetic Variation Genetic Variation Heritability Heritability Survival of the fittest Survival of the fittest

Requirement # 1 Overpopulation  When conditions are too favorable organisms tend to produce more offspring than the environment can support.  When resources are no longer large abundant enough to support every individual in a population competition occurs.

Requirement #2: Struggle for Existence (Competition)  Every organism must constantly fight for limited resources (food, water, mates) and escape from predators in order to survive long enough to reproduce.

Requirement #3: Genetic Variation  Genetic differences among individuals in a population  Causes Meiosis – genetic variation can be increased during crossing over Mutations- can be beneficial

Requirement #4 Heritability  Organisms pass their traits on to their offspring  Organisms resemble their parents both internally and externally

Requirement #5 Survival of the Fit Enough  Individuals best suited/adapted to their environments have the best chances for survival Reproduce more often and pass those good traits on to their offspring. Reproduce more often and pass those good traits on to their offspring.

The Results: Increased frequency of best traits in the population over time Over time good traits appear more in a population because more individuals have alleles for those traits. Over time good traits appear more in a population because more individuals have alleles for those traits. Speciation-If a species changes enough that it can no longer interbreed with the original species a new species can form. Speciation-If a species changes enough that it can no longer interbreed with the original species a new species can form.

Examples of Natural Selection  Sickle Cell Anemia Hereditary disease that affects hemoglobin Hereditary disease that affects hemoglobin Protein in our blood that carries oxygenProtein in our blood that carries oxygen 1/500 have Sickle Cell Anemia in US 1/500 have Sickle Cell Anemia in US 1/100 have Sickle Cell Anemia in Central Africa 1/100 have Sickle Cell Anemia in Central Africa

 Malaria is a warm climate disease caused by a parasites that is transmitted by mosquitoes.  Causes death if not treated.  People with sickle cell anemia are more resistant to malaria AA = normal blood (no resistance)AA = normal blood (no resistance) Aa = both normal and sickle shaped blood (resistance)Aa = both normal and sickle shaped blood (resistance) aa = all sickle shaped blood (resistance)aa = all sickle shaped blood (resistance)

Another Example  The Peppered Moth White or black and sits on the bark of trees White or black and sits on the bark of trees Pray to birds Pray to birds  Industrial revolution Increased pollution Killed lichens on trees Trees covered in lichens appear more white while trees without lichens appear dark

Let’s try this!! Virtual Peppered Moths Virtual Peppered Moths

What Happened?  Lots of Pollution  No pollution

Types of Natural Selection 1) Balanced Selection (Stabilizing Selection) * When selective pressures select against the two extremes of a trait.

2) Directional Selection * When selective pressures are against one extreme.

3) Disruptive Selection * When selection acts against individuals in the middle of the trait.

Types of Adaptations 1) Morphological – structures are adapted to specific needs and environments. Floating Leaves Turtles shell Floating Leaves

2) Behavioral Adaptations – based on behavior Bird Migration Living in herds/schools

3) Physiological Adaptations – Adaptations on a molecular level * Things inside the body vs. outside Bioluminescent –deep seaPoisons- Dart Frog

Types of Reproductive Isolation:  Reproductive Isolation-If a population becomes isolated and can’t interbreed, changes can accumulate and a new species can form  Three Types… 1. Geographical Isolation 2. Temporal Isolation 3. Behavioral Isolation

1) Geographical Isolation  Separation by land forms or physical features Examples: Rivers, mountains, islands Examples: Rivers, mountains, islands Darwin’s Finches Galápagos Islands – had different environmentsGalápagos Islands – had different environments 14 species of finches arose by speciation from a single South American species.14 species of finches arose by speciation from a single South American species. Populations of finches can no longer interbreed.Populations of finches can no longer interbreed.

Finches Beaks

2) Temporal Isolation  Separated by time of day or year reproduce Examples: gamete exchange during different seasons Examples: gamete exchange during different seasons Frogs: Rana aurora - breeds January - March Rana boylei - breeds late March - May Fruit Flys: Drosophila persimilis - breeds in early morning Drosophila pseudoobscura - breeds in the afternoon

3) Behavioral Isolation  Separated by behavior Examples: Bird/frog calls, different courtship behaviors, lighting patterns of lightning bugs. Examples: Bird/frog calls, different courtship behaviors, lighting patterns of lightning bugs.

Patterns in Evolution  Divergence – organisms evolve different traits.  Convergence – organisms with different traits evolve to have the same traits.