Evolutionary Theory

Evolutionary TheoryIdeas on the Origin of LifePasteur showed that life was not spontaneously created from non living material, so how do scientists account for organisms emerging from nonliving material?Chemical evolution: the gradual formation of life from nonliving chemicalsThe Oparin-Haldane HypothesisSince free oxygen destroys organic molecules as fast as they are formed, Alexander Oparin suggested that with energy from lightning and heat from volcanoes, chemicals could combine to form complex organic molecules.J.B.S. Haldane suggested that the sun could react to form these compounds to make virus-like organisms.The Miller-Urey ExperimentStanley Miller and Harold Urey tested part of the Oparin-Haldane hypothesis in 1953Application: the experimentindicated that if the atmosphere was made up ofthese gases, it could haveformed basic organiccompounds.

Alternate IdeasOther scientists believe that the Earths early atmosphere was made up of mainly carbon dioxide.Scientists do not agree what the early atmosphere contained so scientists have come up with two alternative explanations.1. chemical reactions occurred in deep sea vents. However, heat could have destroyed those molecules2. Panspermia: life originated in outer space. A meteorite could have carried organic material to Earth.

Obstacles to Chemical EvolutionThe basic-single celled organism is extremely complex

Cell membrane

DNADNA is the information to make life. How did DNA form? Scientists have been unable to form proteins without enzymes. The DNA double helix is too complex to have formed by natural processes.The First CellAerobic- existing with oxygenAnaerobic- existing without oxygenHeterotrophic unable to make foodAutotrophic able to make food from the sun or other chemicalsProkaryote cell with no nucleusEukaryote cell with a nucleus and other membrane-bound organelles.The First CellFirst cell is thought to be anaerobic, heterotrophic, and prokaryotic.Endosymbiotic Theory attempts to explain the origin of mitochondria and chloroplasts in eukaryotic cells.

Natural SelectionNatural Selection a process that favors organisms that are best adapted to their environment.

Example 1A wild rabbit population that lives in a densely wooded area has genes that can produce white offspring, brown offspring, or black offspring. How could environmental factors and natural selection affect which trait for fur color occurs most often?Natural selection does not produce new traits. It only favors traits already present.

Natural selection in three waysNatural selection affects the distribution of genes in a species in three ways.Stabilizing SelectionNatural Selection which favors average individuals in a populationExample: If an insect is larger than average, it is more visible to animals. If it is too small, it may not be able to capture and eat its prey.Directional SelectionFavors organisms with an extreme form of a trait.Example: Galapagos finches. During droughts, food is scarce. Finches with larger beaks are better suited for survival and reproduction so the average beak size increases.

Disruptive SelectionFavors organisms with extremes in both directions and eliminates the middle.Example: If only very large or very small seeds were available to a species of bird, then the birds with large and small beaks would be advantageous. The birds with average size beaks would decrease.

Consider a flying beetle which is introduced to a new tropical island.Only the beetle with the darkest bodies thriveThe smallest beetles cannot compete for food. The largest beetles are easy prey for birds.The beetles with the smallest wings thrive in rotten tree trunks. The beetles with the largest wings thrive along the coastline.Mutations change the genetic codeIf a mutation occurred in a population of wild rabbits who were brown, what would happen to a animal that had a mutation causing it to be white?Adaptations in animalsCats: have claws that help them catch prey.Pointed teeth that help them tear apart their food.ExampleA mutation occurs in a plant that causes its leaves to taste bitter. In what kind of environment would this mutation be beneficial and more likely passed on to future generation?The gene poolGene pool: The total number of different genes available to a species.The more diverse a population is (the more genes), the better that species is able to adapt to their environment.Example 1How would the environment affect the gene pool if a wild rabbit population of brown, white, and black fur lived in a densely wooded environment?Example 2Sometimes by mere chance, traits could occur more frequently than others. (genetic drift). If a species of insect can have white or brown eyes, and both are equally beneficial, then just by chance more insects are born with brown eyes during a season. How would this affect the gene pool?Would genetic drift affect small or large populations more?Example 3A mouse species lives on a small island. A hurricane kills 80% of all life on the island including the mice. How might this affect the gene pool?Example 4Organisms with a high rate of mutation have a better chance of survival in a changing environment. Why?A bacteria culture is started. After treating the culture with an antibiotic, only 2% of the culture survives. If the culture is left to repopulate, how will it likely respond to future treatment?

SpeciationSpeciation: the formation of new species.Example: If a population gets divided by some natural event like a volcano or separated by a land mass, the two populations can no longer breed together. The newer and smaller population would breed with each other and eventually form new traits and new species. This is called geographic isolation.

Other ways species will not breed with each other include their reproductive cycles could be different or their behavior or courtship rituals are different.

Similarities in speciesHomologous vs Analogous structuresHomologous structures: Different species with similar structures with different functions

Analogous structuresStructures that have similar functions but have different structures

Vestigial OrgansOrgans that seem to have no useful purpose.

Types of EvolutionDivergent: species formed from a common ancestorConvergent: unrelated species evolving similar characteristicsCoevolution: two species evolving together.Divergent

Convergent

Coevolution