Mechanisms for Evolution Lamark vs. Darwin

Differing Viewpoints…  Charles Darwin Characteristics among members of a species vary. Characteristics among members of a species vary. Only individuals with the characteristics best suited to the environment will survive to reproduce. Only individuals with the characteristics best suited to the environment will survive to reproduce. Over time characteristics will increase in the population. Over time characteristics will increase in the population. (Now called Natural Selection) (Now called Natural Selection)

Differing Viewpoints  Jean Lamark Evolution occurs through the use and disuse of physical features. Evolution occurs through the use and disuse of physical features. Over an organisms lifetime features will increases by use or decrease by disuse. Over an organisms lifetime features will increases by use or decrease by disuse. These traits are than passed down to their offspring. These traits are than passed down to their offspring.

Lamark vs. Darwin

Natural Selection  Process by which populations change in response to their environments.  Key components of natural selection: Genetic Variation Genetic Variation Competition and Struggle for existence Competition and Struggle for existence Survival of the fittest (Variation is Selected) Survival of the fittest (Variation is Selected) Increased frequency of best traits (Variation is inherited) Increased frequency of best traits (Variation is inherited)

Requirement #1: Genetic Variation  Exists within a population through Meiosis – genetic variation is increased during crossing over Mutations- spontaneous changes in DNA Genetic Recombination – occurs during sexual reproduction and provides endless source of new variations

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

Requirement # 2 Reproduction Leads to Competition  When conditions are favorable organisms tend to produce many offspring.  When resources become scarce: competition occurs.

Requirement #3 Survival of the Fittest  Individuals best suited/adapted to their environments have the best chances for survival Those individuals Reproduce more often and pass those good traits that allowed survival on to their offspring. Those individuals Reproduce more often and pass those good traits that allowed survival on to their offspring.

End Result: Increased frequency of best traits Over time, good traits appear more in a population because more individuals survive and reproduce. Over time, good traits appear more in a population because more individuals survive and reproduce.

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 parasite 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)

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

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

What Happened?  Lots of Pollution:  No pollution:

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

Another Example  Imagine rabbits with fur that can either be black, grey, or white (due to incomplete dominance)  The environment consists of black rock outcroppings, and white snowy tundra.  Animals that are born with the heterozygous grey coats are going to be spotted easily by their predators. Animals with black or white fur are likely to survive and reproduce more offspring than gray rabbits.

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

Adaptations  An adaptation is an physical structure, physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection. evolvednatural selectionevolvednatural selection  Adaptations increase the reproductive success of the organism. reproductive successorganismreproductive successorganism

Adaptations  Organisms that are adapted to their environment are able to: obtain air, water, food and nutrients obtain air, water, food and nutrients cope with physical conditions such as temperature, light and heat cope with physical conditions such as temperature, light and heat defend themselves from their natural enemies defend themselves from their natural enemies reproduce reproduce respond to changes around them respond to changes around them

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 sea Poisons- Dart Frog

Speciation If a species changes enough that it can no longer interbreed with the original species a new species can form. If a species changes enough that it can no longer interbreed with the original species a new species can form.

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 reproduction occurs 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  Convergence – Unrelated organisms develop similar traits.  Convergence – Unrelated organisms develop similar traits. Different geographical areas sometimes exhibit groups of plants and animals of strikingly similar appearance, even though the organisms may be only distantly related.

Patterns in Evolution  Divergence – two related species become increasingly different. Organisms evolve to fill diverse ecological niches. (In the broadest sense, all current species are the result of divergent evolution.)