1 Origin of Life. Aristotle (384 –322 BC) Proposed the theory of spontaneous generation Proposed the theory of spontaneous generation Also called abiogenesis.

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Origin of Life

Aristotle (384 –322 BC)

• Proposed the theory of spontaneous generation• Also called abiogenesis• Idea that living things can arise from nonliving matter• Idea lasted almost 2000 years

Spontaneous Generation

• For centuries, people based their beliefs on their interpretations of what they saw going on in the world around them without testing their ideas

• They didn’t use the scientific method to arrive at answers to their questions

• Their conclusions were based on untested observations

•Examples of Spontaneous Generation

Example #1

• Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times

Example #1

Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs

Example #2

• Observation: In many parts of Europe, medieval farmers stored grain in barns with thatched roofs (like Shakespeare’s house). As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and of course there were lots of mice around.

Example #2

Conclusion: It was obvious to them that the mice came from the moldy grain.

• Observation: Since there were no refrigerators, the mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses. Typically, carcasses were “hung by their heels,” and customers selected which chunk the butcher would carve off for them.

Example #3

Example #3

Conclusion: Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies.

•Disproving Spontaneous Generation

Francesco Redi (1668)

• In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat

Redi’s Experiment

• Redi used open & closed flasks which contained meat.• His hypothesis was that rotten meat does not turn into flies.• He observed these flasks to see in which one(s) maggots would develop.

Redi’s Findings

• He found that if a flask was closed with a lid so adult flies could not get in, no maggots developed on the rotting meat within.

• In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared.

Redi’s (1626-1697) Experiments Evidence against spontaneous

generation:1. Unsealed – maggots on meat2. Sealed – no maggots on meat3. Gauze – few maggots on gauze, none on meat

Results of Redi’s Experiments

• The results of this experiment disproved the idea of spontaneous generation for larger organisms, but people still thought microscopic organisms like algae or bacteria could arise that way.

How Do Microbes Arise?

• By 1860, the debate had become so heated that the Paris Academy of Sciences offered a prize for any experiments that would help resolve this conflict

• The prize was claimed in 1864 by Louis Pasteur, as he published the results of an experiment he did to disproved spontaneous generation in microscopic organisms

Louis Pasteur (1822-1895)

Pasteur's Problem

• Hypothesis: Microbes come from cells of organisms on dust particles in the air; not the air itself.

• Pasteur put broth into several special S-shaped flasks

• Each flask was boiled and placed at various locations

Pasteur's Experiment - Step 1

• S-shaped Flask• Filled with broth • The special shaped was intended to trap any dust particles containing bacteria

Pasteur's Experiment - Step 2

• Flasks boiled• Microbes Killed

Pasteur's Experiment - Step 3

• Flask left at various locations• Did not turn cloudy• Microbes not found• Notice the dust that collected

in the neck of the flask

Pasteur's Experimental Results

The Theory of Biogenesis

• Pasteur’s S-shaped flask kept microbes out but let air in.

• Proved microbes only come from other microbes (life from life) - biogenesis

•History of Evolutionary Thought

Evolution

Lamarck’s Theory of Evolution• Jean-Baptiste Lamarck, 1809• One Of First Scientists To

Understand That Change Occurs Over Time

• Stated that Changes Are Adaptations To Environment acquired in an organism’s lifetime

• Said acquired changes were passed to offspring

Lamarck’s Theory of Evolution

• Idea called Law of Use and Disuse

• If a body part were used, it got stronger

• If body part NOT used, it deteriorated

• James Hutton, 1795, Scottish geologist=Idea Known as Gradualism

• George Cuvier=Stated that species disappear due to a catastrophic event of the earth’s crust (volcano, earthquake…)

Charles Darwin the Naturalist

Charles Darwin• Born Feb. 12, 1809• Joined Crew of HMS Beagle,

1831• Naturalist• 5 Year Voyage around world• Avid Collector of Flora &

Fauna• Astounded By Variety of

Life

HMS Beagle

Darwin Left England in 1831Darwin returned 5 years later in 1836

HMS Beagle’s Voyage

The Galapagos Islands

• Small Group of Islands 1000 km West of South America

• Very Different Climates• Animals On Islands

Unique• Tortoises• Iguanas• Finches

The Galapagos Islands• Volcanic islands off

the coast of South America

• Island species varied from mainland species & from island-to-island species

• Each island had long or short neck tortoises

The Galapagos Islands

• Finches on the islands resembled a mainland finch

• More types of finches appeared on the islands where the available food was different (seeds, nuts, berries, insects…)

• Finches had different types of beaks adapted to their type of food gathering

• Evolution is the slow , gradual change in a population of organisms over time

Darwin’s Observations & Conclusions

Natural Selection 1• Production of more individuals than can be

supported by the environment leads to a struggle for existence among individuals

• Only a fraction of offspring survive each generation

• Survival of the Fittest

• Individuals of a population vary extensively in their characteristics with no two individuals being exactly alike.

• Much of this variation between individuals is inheritable.

Natural Selection 2

Natural Selection 3

• Individuals who inherit characteristics most fit for their environment are likely to leave more offspring than less fit individuals

• Called Natural Selection

Darwin’s Theory of Evolution• The unequal ability of individuals to survive

and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection)

• New species evolve

Common Descent with Modification

• Darwin proposed that organisms descended from common ancestors

• Idea that organisms change with time, diverging from a common form

• Caused evolution of new species

• Artificial Selection–Selective Breeding To Enhance

Desired Traits Among Stock or Crops

Key Concept:Artificial Selection, Nature Provided The

Variation Among Different Organisms, And Humans Selected Those Variations That They Found Useful

Opposition to Evolution

• The upheaval surrounding evolution began with Darwin’s publication of On the Origin of Species By Means of Natural Selection

• The debate continues nearly 150 years later

Supporting Evidence

Homologous Structures

Fossil Record

Similarities In Embryonic Development

Similarities in DNA Sequence

Evolution of pesticide

resistance in response to

selection

Natural Selection

Population Genetics

The Gene Pool

•Members of a species can interbreed & produce fertile offspring•Species have a shared gene pool•Gene pool – all of the alleles of all individuals in a population

•Different species do NOT exchange genes by interbreeding•Different species that interbreed often produce sterile or less viable offspring e.g. Mule

Populations•A group of the same species living in an area•No two individuals are exactly alike (variations)•More Fit individuals survive & pass on their traits

Speciation•Formation of new species•One species may split into 2 or more species•A species may evolve into a new species•Requires very long periods of time

The Hardy-Weinberg Theorem• Used to describe a non-evolving population.• Shuffling of alleles by meiosis and random

fertilization have no effect on the overall gene pool.

• Natural populations are NOT expected to actually be in Hardy-Weinberg equilibrium.

• Deviation from Hardy-Weinberg equilibrium usually results in evolution

• Understanding a non-evolving population, helps us to understand how evolution occurs

Assumptions of the H-W Theorem1. Large population size

- small populations can have chance fluctuations in allele frequencies (e.g., fire, storm).

2. No migration- immigrants can change the frequency of an allele by bringing in new alleles to a population.

3. No net mutations- if alleles change from one to another, this will change the frequency of those alleles3. Random mating

- if certain traits are more desirable, then individuals with those traits will be selected and this will not allow for random mixing of alleles.

4. No natural selection- if some individuals survive and reproduce at a higher rate than others, then their offspring will carry those genes and the frequency will change for the next generation.

• Microevolution refers to changes in allele frequencies in a gene pool from generation to generation. Represents a gradual change in a population.

• • Causes of microevolution:• • 1) Genetic drift

2) Natural selection (1 & 2 are most important)

3) Gene flow

4) Mutation

Three ways (modes of selection) in which natural selection can affect the contribution that a genotype makes to the next generation.

• Disruptive selection– Selection eliminates intermediate types.

• Directional selection– Selection eliminates one extreme from a

phenotypic array.• Stabilizing selection– Selection acts to eliminate both extremes from an

array of phenotypes.

Forms of Selection