UNIT 12UNIT 12EvolutionEvolution

I.I. How could life have begun on a lifeless Earth?How could life have begun on a lifeless Earth?

A.A. Abiogenesis / Spontaneous GenerationAbiogenesis / Spontaneous Generation

1. 1. Abiogenesis Abiogenesis is the idea that is the idea that life came life came from non-living materialfrom non-living material. This idea is sometimes . This idea is sometimes termed termed spontaneous generationspontaneous generation. .

2. The environment of the early Earth may 2. The environment of the early Earth may have provided a unique set of conditions that have provided a unique set of conditions that

allowed abiogenesis to occur. Researchers now allowed abiogenesis to occur. Researchers now believe that the believe that the early atmosphereearly atmosphere may have may have been been similar to the vapors given off by modern similar to the vapors given off by modern volcanoes: volcanoes: carbon monoxide, carbon dioxide carbon monoxide, carbon dioxide and and nitrogen (note the absence of free nitrogen (note the absence of free atmospheric atmospheric oxygen).oxygen).

a. a. Oparin developed a theory to explain the Oparin developed a theory to explain the development of life on earthdevelopment of life on earth. His theory hypothesized . His theory hypothesized that due to the chemicals in the atmosphere, the lack that due to the chemicals in the atmosphere, the lack of free oxygen, and intense energy from lightening and of free oxygen, and intense energy from lightening and volcanoes volcanoes simple organic molecules could form from simple organic molecules could form from inorganic compoundsinorganic compounds. At this time in earth’s history . At this time in earth’s history the earth was covered by water. Therefore, this the earth was covered by water. Therefore, this essential first step in the development of life must have essential first step in the development of life must have occurred in the oceansoccurred in the oceans. This supports the idea that life . This supports the idea that life originated as a “originated as a “primordial soupprimordial soup” in the oceans. ” in the oceans.

b. b. Miller and Urey designed an experiment to Miller and Urey designed an experiment to test Oparin’s “primordial soup” hypothesistest Oparin’s “primordial soup” hypothesis. They were . They were able to successfully able to successfully mimic the proposed conditions of mimic the proposed conditions of early earth in the laboratoryearly earth in the laboratory. Up to 4% of the carbon . Up to 4% of the carbon was converted to amino acids (the building blocks of was converted to amino acids (the building blocks of proteins). This experiment has been proteins). This experiment has been replicatedreplicated numerous times. numerous times.

c. Additional scientists have developed theories c. Additional scientists have developed theories explaining the explaining the formation of the first living cellsformation of the first living cells from the from the “primordial soup”. However, these theories are more “primordial soup”. However, these theories are more tentativetentative (supported by fewer experiments). (supported by fewer experiments).

B. Biogenesis B. Biogenesis

1. Once life was established in very simple cells, 1. Once life was established in very simple cells, biogenesis began. biogenesis began. Biogenesis is the continuation of Biogenesis is the continuation of life from other living cellslife from other living cells. For a long time people . For a long time people believed that non-living material could produce living believed that non-living material could produce living things (spontaneous generation). For example, it was things (spontaneous generation). For example, it was a common belief that fish arose from the mud in the a common belief that fish arose from the mud in the bottom of a river. bottom of a river.

a. Francesco a. Francesco RediRedi set out to set out to disprove the theory disprove the theory of spontaneous generation/of spontaneous generation/abiogenesis. He abiogenesis. He developed a developed a controlled experimentcontrolled experiment to test his to test his hypothesis that life must come from life (biogenesis).hypothesis that life must come from life (biogenesis).

Redi’s Experiment: Redi’s Experiment:

Control GroupControl Group Experimental Group Experimental Group

Independent VariableIndependent Variable Open jarsOpen jars Covered jars Covered jars

ConstantConstant Rotting meatRotting meat Rotting meat Rotting meat

Observations Observations Flies entered jars, Flies entered jars, Flies were unable to Flies were unable to

landing on the meatlanding on the meat enter the jarenter the jar

ResultsResults Maggots developed Maggots developed No maggots developed No maggots developed

on meaton meat on meaton meat

ConclusionsConclusions The maggots came from the flies, NOT the meat.The maggots came from the flies, NOT the meat.

b. After the development of the b. After the development of the microscopemicroscope and and thus the discovery of thus the discovery of microorganismsmicroorganisms, Redi’s work was , Redi’s work was called into question. Did the microscopic organisms called into question. Did the microscopic organisms come from a vital force in the air or come from a vital force in the air or did biogenesis hold did biogenesis hold true at all levelstrue at all levels??

c. Louis c. Louis PasteurPasteur designed an experiment to designed an experiment to disprove spontaneous generation for microorganismsdisprove spontaneous generation for microorganisms. .

Experimental GroupExperimental Group

Control GroupControl Group

Conclusion Conclusion Microorganism came from microorganisms Microorganism came from microorganisms carried on dust in the air, NOT the air itselfcarried on dust in the air, NOT the air itself. .

C. The evolution of cells C. The evolution of cells

1. Based on the conditions proven by Miller and 1. Based on the conditions proven by Miller and Urey, scientists developed the Urey, scientists developed the heterotroph hypothesisheterotroph hypothesis to explain the to explain the evolution of prokaryotic cellsevolution of prokaryotic cells. .

a. The a. The first cells would have been prokaryoticfirst cells would have been prokaryotic (no nucleus), (no nucleus), anaerobicanaerobic (does not require oxygen), (does not require oxygen), and and heterotrophicheterotrophic (must take in nutrients). (must take in nutrients). Prokaryotic, heterotrophic cells are the Prokaryotic, heterotrophic cells are the simplest cellssimplest cells and therefore most likely to evolve first. and therefore most likely to evolve first. The lack of The lack of free atmospheric oxygen would have required an free atmospheric oxygen would have required an anaerobic cellanaerobic cell. .

b. Over time b. Over time photosynthetic prokaryotic cells photosynthetic prokaryotic cells evolvedevolved, allowing for the , allowing for the release of free oxygenrelease of free oxygen. This . This profoundly profoundly changed earth’s environmentchanged earth’s environment and led to the and led to the development of an ozone layerdevelopment of an ozone layer..

c. The production of oxygen led to conditions c. The production of oxygen led to conditions that favored the evolution of that favored the evolution of aerobic, prokaryotic cellsaerobic, prokaryotic cells..

2. Based on the idea of biogenesis and current 2. Based on the idea of biogenesis and current research in symbiosis, Lynn research in symbiosis, Lynn MarguilisMarguilis developed the developed the endosymbiont hypothesisendosymbiont hypothesis to to explain the development explain the development of eukaryotic cellsof eukaryotic cells. .

a. Diagram of endosymbiont hypothesisa. Diagram of endosymbiont hypothesis

b. b. EvidenceEvidence to support the endosymbiont to support the endosymbiont hypothesis includes the fact that hypothesis includes the fact that chloroplasts and chloroplasts and mitochondria can self replicatemitochondria can self replicate and these organelles and these organelles contain their own circular DNAcontain their own circular DNA..

Review Questions:Review Questions:1. What is abiogenesis?1. What is abiogenesis?

the idea that life came from non-living materialthe idea that life came from non-living material2. What were the conditions of the early atmosphere?2. What were the conditions of the early atmosphere?

carbon monoxide, carbon dioxide and nitrogencarbon monoxide, carbon dioxide and nitrogen 3. What three scientists are credited with developing 3. What three scientists are credited with developing and supporting the theory of these conditions on early and supporting the theory of these conditions on early Earth?Earth?

Oparin, Miller and UreyOparin, Miller and Urey

4. What is biogenesis?4. What is biogenesis?

is the continuation of life from other living cells.is the continuation of life from other living cells.

5. What two scientists disproved spontaneous 5. What two scientists disproved spontaneous generation using controlled experiments?generation using controlled experiments?

Redi and PasteurRedi and Pasteur

6. What does the heterotroph hypothesis explain?6. What does the heterotroph hypothesis explain?

the evolution of prokaryotic cellsthe evolution of prokaryotic cells

7. What does the endosymbiont hypothesis explain?7. What does the endosymbiont hypothesis explain?

the evolution of eukaryotic cellsthe evolution of eukaryotic cells

II. How did all of life on Earth come from a few cells?II. How did all of life on Earth come from a few cells?

A. Theory of EvolutionA. Theory of Evolution

1. 1. Charles DarwinCharles Darwin is credited with the is credited with the development of the theory of evolution, but there were development of the theory of evolution, but there were many people that contributed ideas upon which he many people that contributed ideas upon which he built his own. Darwin also developed his ideas based built his own. Darwin also developed his ideas based on his travels as the ship naturalist on the H.M.S. on his travels as the ship naturalist on the H.M.S. Beagle. Of particular interest to Darwin were the Beagle. Of particular interest to Darwin were the animals of the animals of the Galapagos IslandsGalapagos Islands..

2. In 1859, Darwin and Alfred Wallace jointly proposed 2. In 1859, Darwin and Alfred Wallace jointly proposed that that new species could develop by a process of natural new species could develop by a process of natural selectionselection. The theory can be described as a process:. The theory can be described as a process:

a. a. Variation of traitsVariation of traits within the population leads within the population leads to different phenotypes. Some variations are better to different phenotypes. Some variations are better suited to the current conditions of the environment. suited to the current conditions of the environment.

b. b. OverproductionOverproduction in populations in populations leads to leads to competitioncompetition for limited resources (food, for example). for limited resources (food, for example).

c. c. Natural selection favors the best suited Natural selection favors the best suited phenotype at the timephenotype at the time. This does not necessarily . This does not necessarily mean that those struggling die, but will be in a poorer mean that those struggling die, but will be in a poorer condition.condition.

d.d. The The survivalsurvival (or better success) (or better success) of the best of the best adapted individuals leads to higher reproductive adapted individuals leads to higher reproductive successsuccess. The variations will be passed on to the . The variations will be passed on to the offspring. Over time, if the environment does not offspring. Over time, if the environment does not change, those change, those favorable variations will be seen more favorable variations will be seen more frequently in the population because nature has frequently in the population because nature has “selected” that trait.“selected” that trait.

3. Central to the theory of natural selection is the idea 3. Central to the theory of natural selection is the idea of adaptations. of adaptations. An adaptation is any heritable trait that An adaptation is any heritable trait that suits an organism to its natural function in the suits an organism to its natural function in the environmentenvironment (its niche). There are three basic types of (its niche). There are three basic types of adaptations:adaptations:

a. Examples of a. Examples of structuralstructural adaptations are adaptations are defensive structures, defensive structures, camouflagecamouflage, and , and mimicrymimicry. . Typically, mimicry occurs when a harmless species Typically, mimicry occurs when a harmless species (mountain king snake) resembles a harmful species (mountain king snake) resembles a harmful species (coral snake) using coloration.(coral snake) using coloration.

b. Examples of b. Examples of behavioralbehavioral adaptations are adaptations are herding, schooling, and growlingherding, schooling, and growling

c. Examples of c. Examples of physiologicalphysiological adaptations are adaptations are enzymes, oxygen-binding of hemoglobin, and sightenzymes, oxygen-binding of hemoglobin, and sight

B. Evidence for EvolutionB. Evidence for Evolution

1. Fossil evidence provides an incomplete 1. Fossil evidence provides an incomplete record of early life. record of early life. Fossils can include any evidence Fossils can include any evidence of life, such as imprints and remains of organismsof life, such as imprints and remains of organisms. . This evidence must be interpreted to form an overall This evidence must be interpreted to form an overall picture of how species have changed over time picture of how species have changed over time (evolved). By examining the fossil record, scientists (evolved). By examining the fossil record, scientists have concluded that have concluded that evolution happens in a simple to evolution happens in a simple to complex pattern and life emerged from sea to landcomplex pattern and life emerged from sea to land. . Fossils must be dated to help establish a time frame Fossils must be dated to help establish a time frame for the existence of a species. There are two methods for the existence of a species. There are two methods of determining the age of fossils. of determining the age of fossils.

a. a. In relative dating the exact age of the fossil In relative dating the exact age of the fossil cannot be determined, only the order of appearance cannot be determined, only the order of appearance as compared to other fossils found in nearby rocksas compared to other fossils found in nearby rocks. . Fossils occur in layers of sedimentary rock. The Fossils occur in layers of sedimentary rock. The fossils near the top will be more recent than fossils in fossils near the top will be more recent than fossils in lower layers of rock. lower layers of rock.

b. b. Radioactive dating gives a more exact ageRadioactive dating gives a more exact age using the natural decay of radioactive isotopes in using the natural decay of radioactive isotopes in organisms.organisms.

2. 2. Biochemical similarities include comparisons of DNA Biochemical similarities include comparisons of DNA and the resulting amino acid sequences for certain, and the resulting amino acid sequences for certain, shared proteinsshared proteins. This is considered one of the most . This is considered one of the most reliable and objective types of evidence used to reliable and objective types of evidence used to determine evolutionary relationships. In general, the determine evolutionary relationships. In general, the fewer differences foundfewer differences found between two species, the between two species, the closer the evolutionary relationshipcloser the evolutionary relationship..

3. 3. Shared anatomical structuresShared anatomical structures supports some type supports some type of evolutionary relationship. of evolutionary relationship.

a. a. A similar bone arrangement, even if the A similar bone arrangement, even if the functions are different, supports evolution from a functions are different, supports evolution from a common ancestorcommon ancestor..

b. b. Structures that perform the same function (ex. Structures that perform the same function (ex. flying) but are very different anatomicallyflying) but are very different anatomically (ex. bird wing (ex. bird wing vs. butterfly wing) vs. butterfly wing) supports evolution in similar habitatssupports evolution in similar habitats though not from a recent common ancestor.though not from a recent common ancestor.

c. c. Vestigial structuresVestigial structures (ex. appendix or tail bone (ex. appendix or tail bone in human) in human) are not functional in that organism, but may are not functional in that organism, but may represent a link to a previous ancestorrepresent a link to a previous ancestor..

Review Questions:Review Questions:1. Who is credited with developing the theory of 1. Who is credited with developing the theory of natural selection? natural selection?

Charles DarwinCharles Darwin2. List the four steps in the process of natural 2. List the four steps in the process of natural selection.selection.

Variation of traits, Overproduction of offspring, Variation of traits, Overproduction of offspring, Natural Selection, Survival and reproduction of the Natural Selection, Survival and reproduction of the fittestfittest3. What is an adaptation?3. What is an adaptation?

An adaptation is any heritable trait that suits an An adaptation is any heritable trait that suits an organism to its natural function in the environment organism to its natural function in the environment 4. Name the two methods by which fossils may be 4. Name the two methods by which fossils may be dated. dated.

Relative and Radioactive datingRelative and Radioactive dating

5. How do biochemical similarities support the theory 5. How do biochemical similarities support the theory of evolution?of evolution?

the fewer differences found between two the fewer differences found between two species, the closer the evolutionary relationship.species, the closer the evolutionary relationship.

6. What does similar bone structure (even if the 6. What does similar bone structure (even if the function is different) suggest about two species?function is different) suggest about two species?

supports evolution from a common ancestorsupports evolution from a common ancestor

C.C. Mechanisms of EvolutionMechanisms of Evolution1. 1. Individuals don’t evolve; populations doIndividuals don’t evolve; populations do. The . The

population is the smallest unit of evolutionpopulation is the smallest unit of evolution because because acquired traits in an individual cannot be passed on acquired traits in an individual cannot be passed on (inherited by offspring). However, different traits (inherited by offspring). However, different traits already present in a population can be “selected”, already present in a population can be “selected”, changing the population. changing the population.

2. 2. Evolution occurs when the gene poolEvolution occurs when the gene pool (all of (all of the genes of a population) the genes of a population) changeschanges. A change in . A change in genotype may lead to a change in phenotype. genotype may lead to a change in phenotype. Evolution acts on the phenotypeEvolution acts on the phenotype..

a. Mutations are random changes in DNA and a. Mutations are random changes in DNA and may lead to a new phenotype. may lead to a new phenotype. Mutations provide the Mutations provide the raw material for evolution – diversityraw material for evolution – diversity. For example, a . For example, a mutation causing white fur in Arctic foxes may lead to mutation causing white fur in Arctic foxes may lead to better camouflage in winter.better camouflage in winter.

b. The environment also plays a key role in b. The environment also plays a key role in evolution. evolution. Environmental changes are natures Environmental changes are natures “selection forces” that act upon the phenotype ranges “selection forces” that act upon the phenotype ranges caused by genescaused by genes. There are three basic patterns by . There are three basic patterns by which natural selection occurs:which natural selection occurs:

i. i. StabilizingStabilizing selection favors the selection favors the ““averageaverage” phenotype in a ” phenotype in a population. population.

ii. ii. DirectionalDirectional selection favors selection favors ONEONE of the extremeof the extreme ends of the “typical” ends of the “typical” distribution.distribution.

iii. iii. DisruptivDisruptive Selection favors e Selection favors BOTH of the extremeBOTH of the extreme ends of the ends of the ““typical” distribution.typical” distribution.

3. 3. Coevolution describes the evolutionary effect of Coevolution describes the evolutionary effect of one species upon anotherone species upon another. Coevolution occurs . Coevolution occurs between between species that share a biological relationshipspecies that share a biological relationship, , such as predator/prey or symbiosis. such as predator/prey or symbiosis.

a. The shape of flowers containing nectar acts as a. The shape of flowers containing nectar acts as a “a “selection forceselection force” (the characteristic which drives ” (the characteristic which drives natural selection) for nectar-eating animals. natural selection) for nectar-eating animals.

Example: Example: Hummingbirds with long beaks are Hummingbirds with long beaks are better able to gather nectar from flowersbetter able to gather nectar from flowers

b. The characteristics of the nectar-eating b. The characteristics of the nectar-eating animals (such as color preference) act as a selection animals (such as color preference) act as a selection force for the flowers, because force for the flowers, because these animals provide these animals provide pollinationpollination for the flowers. for the flowers.

Example: Hummingbirds prefer bright flowers. Example: Hummingbirds prefer bright flowers. Because hummingbirds pollinate flowers from which Because hummingbirds pollinate flowers from which they eat, they eat, the bright flowers are chosen more and thus the bright flowers are chosen more and thus are more reproductively successfulare more reproductively successful..

4. 4. Speciation is the development of a new speciesSpeciation is the development of a new species. A . A species is defined as a group of organisms that can species is defined as a group of organisms that can produce fertile offspring. produce fertile offspring. Speciation occurs when a Speciation occurs when a population is separated, usually due to a geographical population is separated, usually due to a geographical barrier, and natural selection changes the population barrier, and natural selection changes the population so much the two groups could no longer interbreedso much the two groups could no longer interbreed. . Therefore, geographic isolation leads to reproductive Therefore, geographic isolation leads to reproductive isolation. isolation.

D. Timeframes of evolution differ based on the D. Timeframes of evolution differ based on the environment and the population. environment and the population. The fossil record The fossil record provides evidence for two rates of speciationprovides evidence for two rates of speciation::

1. 1. GradualismGradualism describes speciation that occurs describes speciation that occurs over a long period of time due to the over a long period of time due to the accumulation of accumulation of small changessmall changes. .

2. 2. Punctuated equilibriumPunctuated equilibrium describes speciation describes speciation that occurs in that occurs in rapid bursts that may be separated by rapid bursts that may be separated by 1000’s of years of stability1000’s of years of stability. The primary stimulus is . The primary stimulus is environmental change. environmental change.

Review Questions:Review Questions:

1.1. Why can’t individuals evolve?Why can’t individuals evolve?Only populations can evolve

2.2. What provides the raw material for evolution?What provides the raw material for evolution?Mutations

3.3. What are the three types of natural selection? What are the three types of natural selection?

Stabilizing, Directional, Disruptive

4.4. What is speciation? What is speciation? Formation of a new species

5.5. What condition leads to reproductive isolation? What condition leads to reproductive isolation?

Geographic isolation

6.6. Name the two time frames for speciation. Name the two time frames for speciation. Gradualism and punctuated equilibrium

III. Does evolution still happen today?III. Does evolution still happen today?

A. A. As long as variation, overproduction, As long as variation, overproduction, competition, natural selection and mutations occur, competition, natural selection and mutations occur, evolution will occurevolution will occur. Because evolution leading to . Because evolution leading to speciation happens over such a long period of time, speciation happens over such a long period of time, speciation is not readily observable within a lab. speciation is not readily observable within a lab.

B. B. Natural selectionNatural selection, one of the main , one of the main mechanisms of evolution, mechanisms of evolution, is observable in some is observable in some populationspopulations. For example, the evolution of resistance:. For example, the evolution of resistance:

1. Farmers use pesticides to eliminate insects. 1. Farmers use pesticides to eliminate insects. In a In a population of insects, some individuals will possess population of insects, some individuals will possess genetic immunity to certain chemicalsgenetic immunity to certain chemicals. When the . When the chemicals are applied, the chemicals are applied, the individuals with genetic individuals with genetic immunity will survive and reproduce, passing this immunity will survive and reproduce, passing this resistance to the next generationresistance to the next generation of offspring. Over of offspring. Over time, more individuals are born with this immunity, time, more individuals are born with this immunity, rendering the pesticide useless.rendering the pesticide useless.

2. Antibiotics are drugs that fight bacterial infections. 2. Antibiotics are drugs that fight bacterial infections. Within any population there is genetic variation. In the Within any population there is genetic variation. In the case of antibiotic resistance, case of antibiotic resistance, some bacteria are some bacteria are genetically more resistant to the antibiotic than other genetically more resistant to the antibiotic than other bacteriabacteria. If the amount of antibiotic delivered is too . If the amount of antibiotic delivered is too low or the full course not completed, only those least low or the full course not completed, only those least resistant will die. resistant will die. The surviving, resistant bacteria will The surviving, resistant bacteria will reproducereproduce. With future applications of antibiotics the . With future applications of antibiotics the population is selected to become more and more population is selected to become more and more resistant. resistant. The overuse of antibiotics has led to many The overuse of antibiotics has led to many resistant strains of bacteriaresistant strains of bacteria. .

Review Questions:Review Questions:1.1.What is a pesticide?What is a pesticide?

Chemical to kill bugs

2.2.Why do some insects become resistant Why do some insects become resistant to pesticides?to pesticides?

They have a specific gene 3.3.What is an antibiotic? What is an antibiotic?

Chemical used to kill bactieria

4.4.What has led to the many resistant What has led to the many resistant strains of bacteria? strains of bacteria?

Overuse of antibiotics