Evolution UnitChapters 14, 15, & 16

Ch. 14 History of Life14.1 Biogenesis

Biogenesis: the principle that all living things come from other living things.

Pre-seventeenth century thinking: spontaneous generation

Three scientists from our history ran controlled experiments to prove and disprove ‘thinking’ of the time…Redi, Spallanzani, and Pasteur.

Francisco Redi (1626-1697)-Italian-studied developmental forms of flies-questioned the commonly held belief of the time that flies spontaneously generated from rotting meat.

Lazzaro Spallanzani (1729-1799)-Italian-worked with microscopes-ran experiments to test the spontaneous generation theory using boiled meat broth.-Critics said his work was flawed.

Louis Pasteur (1822-1895)-French-followed Spallanzani’s experiment, made it more scientific and convincing.-Used curved-neck flasks-Biogenesis was finally accepted by the scientific community.-Pasteurization

14.2 Earth’s HistoryIf spontaneous generation does not occur, how did cell-based life arise on Earth?-This question continues to be debated and tested even today.

-5 billion years ago…solar system was a swirling cloud of dust and gas.-Scientists think the planets were formed by repeated collisions of space debris.-Earth formed approximately 4.6 billion years ago.-Determined by studying Earth’s layers of sedimentary rock and modern testing techniques.

Modern Testing Technique:Radiometric Dating

-Measure the decay of radioactive isotopes of the elements. -Determine the half-life of an isotope.-The quantity of a particular radioactive isotope in a sample of material can be measured to determine the materials age.

Examples:

Carbon has a half-life of 5,730 years; can be used to date organic matter up to about 50,000-60,000 years.

Uranium-235 704,000,000 yearsPotassium-40 1,250,000,000 yearsUranium-238 4,500,000,000 years

-worksheet

First Organic Compounds…?Alexander Oparin and John Haldane (1920’s)

-Their hypothesis: At high temperatures and the right conditions, could these elements and compounds combine to form simple amino acids?

-Ingredients: They thought the Earth’s early atmosphere contained NH3 (ammonia) H2 (hydrogen gas), H2O vapor, and CH4 (methane).

-Could the simple amino acids formed go through chemical reactions to form proteins, essential for life.

-When the Earth cooled, did water vapor condensed to form bodies of water?

-These two scientists did not run any experiments; just developed the hypothesis.

Stanley Miller and Harold Urey (1953)-ran experiments using Oparin’s hypothesis.-the hypothesis was proven true.-scientists have been able to create amino acids, ATP, and nucleotides and other organic compounds.

-Other scientists believe organic compounds could be from space.

-Evidence: In 1970 a mixture of organic compounds was found in a newly fallen meteorite.

14.3 The First Life-Forms-Many competing hypotheses about transitions from simple organic molecules to cellular life.

-No clear answer.

-DNA-RNA: Possible relationship to determine an origin of heredity.

-Thomas Cech (1980’s): certain types of RNA is able to act as a chemical catalyst, ribozyme, and promote a chemical reaction…could early cell like structures have been formed?

-First cells discovered (fossils) were prokaryotic like, heterotrophic, living in the absence of oxygen. (3.5 bya)

Early prokaryotes fossils resemble modern day archaeabacteria.

-live in anaerobic environments (no oxygen)-obtain energy by chemosynthesis usingCO2 as a carbon source or H2S.

-3 bya: fossilized prokaryotes similar to modern day cyanobacteria:

-photosynthetic -live in colonies and create stromatolites.

-oxygen gas was produced O2, split into O, andthen combined into ozone O3.-formation of ozone formed a protective layer to shield organisms from the sun’s harmful UV rays.

The First Eukaryotes:

-1.5 bya. fossilized first eukaryotes.-Eukaryotes needed oxygen to survive (aerobes).

-Lynn Margulis (1966) Endosymbiotic Theory: 1. Existing aerobic prokaryotes of the time

were engulfed by eukaryotic type cells and became the cellular structure mitochondria.

2. Cyanobacteria of the time were engulfed by eukaryotic type cells and became chloroplasts.

Summary: the fossil record can be used to determine what organisms existed in the past and their relative age to one another.

Ch. 15 Theory of Evolution

Evolution- a genetic change in a population over a long period of time; also called an adaptation.

Recall: genetic changes (variation) can occur from mutations in the DNA/RNA code and crossing over during meiosis.

15.1 History of Evolutionary ThoughtJean Baptiste Lamarck (1744-1829):

-thought simple organisms could evolve from nonliving matter.-thought individuals could acquire traits during their life based

upon experiences or behavior and then pass those traits on to future offspring.

-his ideas have been rejected.

Georges Cuvier (1769-1832):-studies fossils and rock strata. -studies the extinction of organisms.-proposed the idea of catastrophism; the idea that sudden geologic

processes could cause the extinction of large groups of organisms.

Charles Lyell (1797-1875):-agreed with some of Cuvier’s ideas but

proposed the theory of uniformitarianism; the idea that geologic processes that were at work in Earth’s past are also at work today.

Charles Darwin (1809-1882) & Alfred Wallace (1823-1913)-Published book in 1859: On the Origin of Species by Means of Natural Selection. Book was based upon his travels around the world; South America, Australia, Galapagos Islands.

-Two goals of the book:1. Present evidence that evolution occurs.2. Explain the variety and distribution of

organisms based on their physical traits (phenotypes).

Darwin’s Proposed the idea of “Natural Selection”.His reasoning:

1. Overproduction- too many offspring being produced; population is limited by disease, lack of food; results in death or decrease in birth rate.

2. Genetic Variation- within a population individuals have different traits.3. Struggle to Survive- individuals compete to survive; those organisms

best adapted to compete in that environment will survive.4. Differential Reproduction- organisms with the best adaptations will

survive and reproduce passing along the adaptations to future, stronger generations.

Also used the phrase, “survival of the fittest” to describe natural selection.

Fitness- ability of an organism to pass its traits on to the next generation.

Among the Evolutionist teachings of today, Natural Selection is the accepted means by which evolution occurs.

Summary: Those individuals with traits that make them better able to compete and reproduce producing fertile offspring will survive and carry on the species.

15.2 Evidence of Evolution (4)1. The Fossil Record: remains or traces of organisms that have died; the most powerful evidence for evolution.

Scientists use the following principals regarding the Fossil Record to provide Evidence for Evolution:

Superposition- if rock at a particular location is undisturbed, the lowest rock was formed before the rock above it.

Relative Age- refer to the geologic time scale; determines which organism is older/younger; not actual age.

Absolute Age- use radiometric dating to determine the actual age of a rock or organsim.

Distribution- compare fossils that were found class to one another in the geologic record to make comparisons as well as the distribution around the world; plate tectonics.

Transitional Species- organisms with features that are intermediate between those of ancestors and newer descendant species. Example: modern whales have forelimb bones that are flippers similar to the forelimbs of a mammal that walked on land.

2. Biogeography-the study of the locations of organisms around the world.

-organisms found around the world are closely related, but have slight adaptations to the environments in which they live.

3. Anatomy & Embryology-the body structure of organisms and how organisms develop.

-organisms that have similar body parts and developmental patterns; but may use the body parts differently.

Homologous Structures- Similar body parts that occur in different organisms that originated from a common ancestor; body parts can be used for different purposes. (Examples: human, bird, bat, cat, & whale bones)

Analogous Structures- body parts with similar functions in organisms, but did not originate from the same common ancestor. (Examples: bird and insect wings)

Vestigial Structures- body parts that serve no purpose in an organism but serve a purpose in other organisms. (Examples: appendix/tail bone in humans; pelvis & femur in whales)

4. Biological Molecules-DNA and RNA; compare the biomolecules and look for similarities and differences.

-The more similar sequences and amount of DNA/RNA organisms have, the more likelihood those organisms are related to a common ancestor.

15.3 Evolution in ActionEvolution is a continuous process, always changing.

Types of Evolution:

Convergent Evolution- different species evolve similar traits.

Divergent Evolution- descendants of a single ancestor diversify into new species that each fit different parts of the environment; the organisms develop traits that allow that species a better chance to survive.

Adaptive Radiation- type of divergent evolution where the new species of organism formed fills many parts of the environment.

Artificial Selection- we select the traits we want; those traits continue through generations.Example: Humans creating new dog breeds.

Coevolution- when two or more species have evolved adaptations to each other’s influence.Examples: antibiotic resistant bacteria, insect resistant pesticides, plants using insects to carry pollen, microbes living inside other organisms.

Ch. 16 Population Genetics and Speciation16.1 Genetic EquilibriumThe study of evolution from a genetic point of view is called population genetics, also called microevolution.

-this study involves looking at variations in genes within populations for various traits.

-the population is the smallest unit in which evolution can occur.

Variations in traits occur normally within populations. Examples: height and weight.

Causes of Variations:1. Mutations: if the DNA mutation allows

organisms to become more fit for their environment, the mutation will be passed to further generations.

2. Recombination: independent assortment and crossing-over of genetic material in meiosis.

3. Random pairing of gametes: the union of the gametes (sperm & eggs) in reproduction is random.

Scientists needed a model to understand what forces in nature disrupt genetic equilibrium….in other words why is it organisms are all not the same?

Hardy-Weinberg Genetic Equilibrium:1. No net mutations occur.2. Individuals may not enter or leave a population.3. The population is large.4. Individuals mate randomly.5. Selection does not occur.

*True genetic equilibrium is a theoretical state.

16.2 Disruption of Genetic EquilibriumRecall: any exceptions in the Hardy-Weinberg Equilibrium can result in evolution.

1. MutationsA: Mutations occur constantly at very low rates under normal conditions.

-Mutations from mutagens happen constantly and can affect the genetic equilibrium; good or bad.

2. Gene FlowA: the size of the population must remain constant.

-in nature, populations experience immigration and emigration; this disrupts the equilibrium.

3. Genetic DriftA: the population must remain large.

-allele frequencies (traits) change in populations leading to genetic drift.-the smaller the population, the greater the degree of evolution; larger populations tend to remain more stable.

4. Nonrandom MatingA: random mating must occur to maintain equilibrium.

-in nature, many species do not mate randomly. -mate selection is influenced by many factors; for example geographic location.-this can lead to inbreeding, which can amplify negative traits.-Assortative mating occurs when organisms select a mate based upon similar physical characteristics.

5. Natural SelectionA: natural selection must be absent to maintain the equilibrium.

-certain organisms can better compete against other organisms leading to survival.-three patterns of natural selection:

1. stabilizing selection (prefers the middle)2. disruptive selection (prefers the extremes)3. directional selection (prefers one extreme)

Stabilizing

Disruptive

16.3 Formation of Species-Speciation is the process of species formation, now commonly called macroevolution.

-Two types of Speciation:1. Allopatric (different homelands)2. Sympatric (together homeland)

-Mechanisms for Speciation:1. Geographic Isolation : physical separation of members of a population; leads to Allopatric Speciation. Examples: canyon, river, mountain range.2. Reproductive Isolation : reasons that cause successful breeding groups within a population to not reproduce; leads to Sympatric Speciation. Examples: death or sterility of offspring; improper mating calls and/or timing during the year.

Rates of Speciation-can require millions of years for a new species to form; however speciation can occur more rapidly.

1. Gradualism (Darwin): regular rate of speciation; slow constant rate.

2. Punctuated Equilibrium (1972 Eldredge and Gould): sudden, rapid change leading to speciation.

In closing…

All of the theories on Evolution presented have something in common:

-the scientist’s have attempted to explain the observed phenomenon with well supported explanations and sometimes evidence.