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Evolutionary Theory. Ideas on the Origin of Life. Pasteur 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 chemicals.
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Ideas on the Origin of Life • Pasteur 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 chemicals
The Oparin-Haldane Hypothesis • Since 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 Experiment • Stanley Miller and Harold Urey tested part of the Oparin-Haldane hypothesis • in 1953 • Application: the experiment • indicated that if the • atmosphere was made up of • these gases, it could have • formed basic organic • compounds.
Alternate Ideas • Other scientists believe that the Earth’s 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 molecules • 2. Panspermia: life originated in outer space. A meteorite could have carried organic material to Earth.
Obstacles to Chemical Evolution • The basic-single celled organism is extremely complex
DNA • DNA 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 Cell • Aerobic- existing with oxygen • Anaerobic- existing without oxygen • Heterotrophic – unable to make food • Autotrophic – able to make food from the sun or other chemicals • Prokaryote – cell with no nucleus • Eukaryote – cell with a nucleus and other membrane-bound organelles.
The First Cell • First cell is thought to be anaerobic, heterotrophic, and prokaryotic. • Endosymbiotic Theory attempts to explain the origin of mitochondria and chloroplasts in eukaryotic cells.
Natural Selection • Natural Selection – a process that favors organisms that are best adapted to their environment.
Example 1 • A 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 ways • Natural selection affects the distribution of genes in a species in three ways.
Stabilizing Selection • Natural Selection which favors average individuals in a population • Example: 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 Selection • Favors 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 Selection • Favors 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 thrive • The 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 code • If 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 animals • Cats: have claws that help them catch prey. • Pointed teeth that help them tear apart their food.
Example • A 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 pool • Gene 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 1 • How 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 2 • Sometimes 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 3 • A 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 4 • Organisms 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?
Speciation • Speciation: 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 species • Homologous vs Analogous structures • Homologous structures: Different species with similar structures with different functions
Analogous structures • Structures that have similar functions but have different structures
Vestigial Organs • Organs that seem to have no useful purpose.
Types of Evolution • Divergent: species formed from a common ancestor • Convergent: unrelated species evolving similar characteristics • Coevolution: two species evolving together.
