EVOLUTION BELL RINGER When you think of the

EVOLUTION BELL RINGER: When you think of the words evolution and natural selection what comes to mind? What do you already know about these topics?

TEST CORRECTIONS: For each question: 1. Write the correct answer 2. Explain why this is the correct answer.

Spontaneous Generation For much of history, people believed that animals could come from non-living sources. They thought: Frogs developed from falling drops of rain mice arose from sweaty underwear and flies arose from decaying meat. This is called abiogenesis Also known as spontaneous generation

These ideas were followed because people simply accepted what they were told

1668 -- Francisco Redi (Italian physician & poet)-- attempted to disprove theory of Spontaneous Generation.

“The flesh of dead animals cannot engender worms unless the eggs of the living being deposited therein” Put dead snakes, eels, and veal in large wide mouthed vessels. Sealed one set with wax and left the other set open to air. Decaying meat was teeming with maggots, sealed meat had no maggots Wax sealed vessels failed to produce maggots because flies were unable to reach the meat

Redi’s critics said: You have too many variables There is a lack of access and a lack of air. We ALL know that everything needs air Of course no flies grew! You haven’t proven anything.

Redi part 2 – answer to critics fine mesh allows in air, but not flies laid eggs on top of mesh no maggots in meat

Redi’s Conclusions: “All living beings come from seeds of the plants or animals themselves” However, if someone were to demonstrate even one exception to this hypothesis, then Redi’s hypothesis would be rejected.

John Needham (English Clergyman) wondered if he could support spontaneous generation of microbes from broth Everyone knew that boiling killed organisms. Needham prepared various broths and showed that they contained microbes. Then he boiled them, and showed that there were no longer any microbes. He ensured the stoppers were loose, so that air would not be excluded Then, after a few days, microbes had reappeared! This was “proof” that the microbes had spontaneously generated from the non-living broth.

Needham’s error BUT: how was this evidence of a faulty experiment? what ERROR in experimental method is shown here? Hypothesis: microbes MUST HAVE arisen spontaneously from the broth. Assumption: there is no other place the microbes could come from (other than the broth). error: microbes could have come from the air!

Spallanzani’s (Italian Naturalist) - 1745 Disagreed with Needham Claimed he didn’t seal jars well enough He said microbes could have come from the air He repeated Needham’s experiment, but changed two things: boiled flasks longer, and SEALED THEM after boiling by fusing the glass tops shut (hermetically sealed – absolutely airtight) Result: NO growth in ANY flask

Needham criticizes Spallanzani’s first experiment BUT Needham said: you boiled it TOO LONG, and: You spoiled the vegetative power by boiling. You killed the ability of the broth to give life. Life can still come from broth -- but the broth must not be “damaged” by boiling.

Spallanzani’s second experiment he did TIMED BOILINGS then left them partially sealed some partially sealed, some hermetically sealed as in his previous experiment hypothesized that more boiling should lead to less life he left some jars as Needham had (leaky seals), to ensure “active principle” was not damaged 30 mins 60 mins 90 mins 120 mins tight seal loose seal

Spallanzani’s second experiment -- results this showed 30 mins TWO main things: 60 mins boiling did NOT damage broth’s ability to support life 90 mins growth depended on the SEAL only 120 mins tight seal loose seal

Louis Pasteur (French chemist) entered a contest sponsored by French Academy of Sciences to prove or disprove Spontaneous generation. 1859– used swan-necked flask allowed in air, but trapped dust (and microbes) boiled infusion showed that NO growth occurred, even after many days BUT -- what about damaging the “active principle”?

Pasteur showed that the active principle was NOT damaged at any later time, he could tip the flask this allowed nutrient broth to contact the dust this carried microbes into the broth result: growth! area where dust had been trapped

Pasteur squashes the idea of abiogenesis completely! Since then, no one has been able to refute Pasteur’s experiment scientists everywhere soon came to accept that abiogenesis did NOT EXIST. but: then how did life on this planet start in the first place?

Early earth – Theory of Origin of Life Some scientists believe Earth is about 4. 6 billion years old Lightening, volcanoes, meteorites, and UV light made conditions intolerable for life Atmosphere was also toxic

Simple molecules All life forms from common ancestor First organisms primitive, unicellular type Energy sources broke the gas molecules and simple organic compounds formed Simple molecules washed into oceans and made larger ones What makes molecules organic? ? Theory of Chemical Evolution: The formation of complex organic molecules from simpler inorganic molecules through chemical reactions in the oceans during the early history of the Earth.

Why do they think this? !? ! Miller and Urey American chemists who simulated Earth’s early atmosphere. Their study showed how organic compounds necessary for life could have arisen from the inorganic compounds present on primitive Earth.

Miller and Urey Experiment Rebuttal Miller and Urey used a nice combination of methane, hydrogen and ammonia gas. Problem: The atmosphere at that time would have been made mostly of carbon dioxide and nitrogen gas and oxygen. If they added these gasses into the mixture they would have not been able to form any amino acids.

Puzzle of Life’s Origin A stew of organic molecules is a long way from a living cell and the lap from nonlife to life is the greatest gap in scientific hypothesis of Earth’s History. Another unanswered question is the formation of DNA and RNA. Scientists cannot solve this puzzle.

The first organisms – heterotrophs Primitive pre-cells were combination of polypeptides, nucleotides, and carbohydrates Could not use energy or reproduce Source of DNA unknown Required outside energy source to reproduce Similar to present day bacteria

Later organisms - autotrophs Autotrophs – capable of making own food Developed when food supply became scarce Photosynthetic organisms evolved from these autotrophs Photosynthesis produced the oxygen for future organisms Oxygen production formed Ozone for atmosphere Blocked UV rays, many new organisms could evolve

How did we go from the original life forms to what we see today? What do we mean by organisms evolving?

The Theory of (Biological) Evolution: Change over time/descent with modification. More specifically, the process by which inherited traits within populations change over time Can eventually lead to the development of distinct populations and new species from preexisting organisms. Individual organisms do not evolve. Evolution can be looked at from the level of the change in gene frequencies from generation to generation and also at the level of the descent of new species from common ancestors over several generations. ***REMINDER!!! Population: A group of organisms of the same species that live in a specific area and reproduce together. http: //evolution. berkeley. edu/evolibrary/article/0_0_0/evo_02

Evolution : We need to answer the question of how evolution actually happens. What is the driving force behind it? How does the change happen?

Factors that can cause evolution that we will talk about this unit… Mutations Natural selection (natural selection) Artificial selection Gene flow via immigration or emmigration Genetic drift--founder effect and bottleneck effect Nonrandom mating like sexual selection * A key ingredient in all of this is variation…there needs to be variation for evolution to take place!

Darwin’s Theory of Natural Selection Natural selection: The process by which individuals that are better adapted to their environment survive and reproduce more successfully than less well adapted individuals.

Breeding Bunnies Lab!