EVOLUTION Chapters 15-17

Warm Up Exercise

• Please complete the evolution pretest that you

picked up as you came in.

Darwin’s Theory of Evolution

• Evolution- “change over time”- the process by

which modern organisms have descended from

ancient organisms.

• Theory- a well-supported, testable explanation of

phenomena that have occurred in the natural

world.

• Charles Darwin- joined the crew of the

HMS Beagle and set sail for a voyage

around the world. During his travels,

Darwin collected evidence that led him

to propose the theory of evolution.

Darwin’s Theory of Evolution

• Galapagos Islands- Darwin observed that the

characteristics of many animals and plants varied

noticeably among the different islands of the

Galapagos.

Exit Slip

• Darwin found fossils of many organisms that were

different from any living species. How would this

finding have affected his understanding of life’s

diversity?

Warm Up Exercise

• Define evolution.

• Why is evolution referred to as a theory?

An Ancient, Changing Earth

• James Hutton- proposed that layers of rock form

slowly and that rocks are shaped by natural

forces that operate over millions of years.

• Charles Lyell- wrote Principles of Geology,

which explained that processes that changed

Earth in the past are still operating in the present.

Lamarck’s Evolution Hypothesis

• Jean-Baptiste Lamarck- proposed that by

selective use or disuse of organs, organisms

acquired or lost certain traits during their lifetime.

These traits could then be passed on to their

offspring. Over time, this process led to change

in a species.

• Lamarck’s hypothesis is now known to be incorrect.

While organisms to adapt to their environment, an

organism’s behavior has no effect on its heritable

characteristics.

Population Growth

• Thomas Malthus- reasoned that if human

population continued to grow unchecked, sooner

or later there would be insufficient living space

and food for everyone.

Darwin Presents His Case

• Alfred Russel Wallace- a naturalist, like Darwin,

who wrote an essay summarizing his thoughts on

evolutionary change.

• On the Origin of Species- Darwin’s book,

published in 1859. Here he poses a mechanism

for evolution that he called natural selection.

Exit Slip

• What did Hutton, Lyell, Lamarck and Malthus

teach us about evolution?

Warm Up Exercise

• What did you observe about the different

appendages in the lab from last class? What

happened if one appendage didn’t serve its

purpose very well?

• Can you think of an example of evolution that you

know?

Inherited Variation and Artificial Selection

• Artificial Selection- nature provides the variation

and humans select the variations that they find

useful.

Evolution By Natural Selection

• Struggle for Existence- members of each species

compete to obtain food, living space, and other

necessities of life.

• Fitness- the ability of an individual to survive and

reproduce in its specific environment.

• Adaptation- any inherited characteristic that increases an

organism’s chance for survival.

• Successful adaptations enable organisms to become better suited

to their environment and thus better able to survive and reproduce.

Evolution By Natural Selection

• Survival of the Fittest- individuals that are better

suited to their environment and have adaptations

that enable fitness, survive and reproduce most

successfully. Individuals with characteristics that

are not well suited to their environment have low

levels of fitness, and either die or leave few

offspring.

• Darwin referred to this idea as natural selection.

• Over time, natural selection results in changes in the

inherited characteristics of a population. These

changes increase a species’ fitness in its environment.

Descent with Modification

• Descent With Modification- over time, natural

selection produces organisms that have different

structures and establish different niches. As a

result, species today look different from their

ancestors.

• Common Descent- all species- living and

extinct- are derived from common ancestors,

therefore a single “tree of life” links all living

things.

Evidence of Evolution

• The fossil record

• Geographic distribution of

living species

Evidence of Evolution

• Homologous body structures

• Homologous Structures- structures that have different

mature forms but develop from the same embryonic

tissues.

• Vestigial Organs- organs that are reduced in size that

they are traces of homologous organs in other species.

Evidence of Evolution

• Similarities in embryology/early

development.

Summary of Darwin’s Theory

• Individual organisms differ and some of this variation is

heritable.

• Organisms produce more offspring than can survive and

many that do survive do not reproduce.

• Because more organisms are produced than can survive,

they compete for limited resources.

• Each unique species has different advantages and

disadvantages in the struggle for existence.

• Species alive today are descended with modification from

ancestral species. They evolved from common ancestors

which unites all organisms in a single tree of life.

Warm Up Exercise

• Name three bits of evidence that scientists have

provided to support the theory of evolution.

Genes and Variation

• Changes in genes produce heritable variation on which

natural selection can operate.

• Gene Pool- consists of all genes, including all the

different alleles that are present in a population.

• Relative Frequency- the number of times an allele

occurs in a gene pool, compared with the number of times

other alleles for the same gene occur.

• Typically expressed as a percentage.

• Has nothing to do with dominant/recessive.

• In genetic terms, evolution is any change in the relative

frequency of alleles in a population.

Sources of Genetic Variation

• Mutations

• A mutation is any change in the DNA sequence, but mutations do

not always affect an organism’s phenotype.

• Mutations can be harmful, beneficial, or neutral.

• Gene Shuffling (in sexual reproduction only)

• The 23 pairs of chromosomes found in humans can form 8.4 million

different combinations of genes- before crossing over.

• Gene shuffling produces many different combinations of genes, but

does not alter the relative frequencies of each type of allele in the

population.

Single Gene and Polygenic Traits

• The number of phenotypes produced for a given trait

depends on how many genes control the trait.

• Single Gene Trait- a trait controlled by a single gene with

two alleles. (ex: widow’s peak)

• Polygenic Trait- a trait controlled by two or more genes.

Each of these genes often has two or more alleles. As a

result, one polygenic trait can have many possible

genotypes and phenotypes. (ex: height in humans)

Exit Slip

• In genetic terms, what indicates that a poluation

is evolving?

• What two processes can lead to inherited

variation in populations?

• How does the range of phenotypes differ between

single-gene traits and polygenic traits?

• How does mutation affect genetic variation?

Warm Up Exercise

• What are the two main sources of genetic variation?

• What is the relationship between relative frequency and

the gene pool?

Natural Selection on Single Gene Traits

• Populations evolve, not individual organisms.

• Natural selection on single-gene traits can lead to

changes in allele frequencies and thus to evolution.

Natural Selection on Polygenic Traits

• Directional Selection- when individuals at one end of the

curve have higher fitness than individuals at another end

of the curve, directional selection takes place.

Natural Selection on Polygenic Traits

• Stabilizing Selection- when individuals near the center of

the curve have higher fitness than individuals at either

end of the curve, stabilizing selection takes place.

Natural Selection on Polygenic Traits

• Disruptive Selection- when individuals at the upper and

lower ends of the curve have higher fitness than

individuals near the middle, disruptive selection takes

place.

Genetic Drift

• Genetic Drift- random change in allele frequencies that

occurs in small populations

• Founder Effect- allele frequencies change as a result of

the migration of a small subgroup of a population.

Evolution vs. Genetic Equilibrium

• Hardy-Weinberg Principle- allele frequencies in

a population will remain constant unless one or

more factors cause those frequencies to change.

• Genetic Equilibrium- the situation in which allele

frequencies remain constant.

Evolution vs. Genetic Equilibrium

• Five conditions are required to maintain genetic

equilibrium:

• There must be random mating.

• The population must be very large.

• There can be no movement into or out of the

population.

• There can be no mutations

• There can be no natural selection.

If these conditions are not met, then equilibrium

will be disrupted and the population will evolve.

Exit Slip

• Draw a graph for each of the three types of

natural selection.

Warm Up Exercise

• What five statements must hold true in order to

maintain genetic equilibrium- according to Hardy

Weinberg?

Speciation

• Speciation- the formation of new species.

• As new species evolve, populations become

reproductively isolated from each other.

• Reproductive Isolation- when the members of

two populations cannot interbreed and produce

fertile offspring.

Types of Reproductive Isolation

• Behavioral Isolation- occurs when two populations are

capable of interbreeding but have differences in courtship

rituals or other reproductive strategies that involve

behavior. (ex: birds with different mating songs)

• Geographic Isolation- two populations are separated by

geographic barriers such as rivers, mountains, or bodies

of water. (ex: Colorodo river separates two types of

squirrels)

• Temporal Isolation- two or more species reproduce at

different times. (ex: flowers releasing pollen at different

times of year)

Testing Natural Selection in Nature

Speciation in Darwin’s Finches

• Founders Arrive- finches from South American mainland (species

A) populated the Galapagos.

• Geographic Isolation- birds from species A crossed to another

Galapagos island. The two populations became isolated from one

another and had different gene pools.

• Changes in the Gene Pool- populations on the new island adapted

to their environment, forming population B.

• Reproductive Isolation- because of their adaptations and different

beaks, species A and B do not mate together if they come in

contact.

• Ecological Competition- during dry season, individuals compete for

food, and over time birds evolve better beaks (species C).

• Continued Evolution- this process continues over several

generations and over times produces the 13 species seen today.

Exit Slip

• Suppose that drought on an island eliminates all

but plants that produces large, tough seeds. All

the finches on the island have very small beaks.

How might this environment change impact the

survival of this finch population?

Warm Up Exercise

• Provide an example for each of the three types of

reproductive isolation.

Fossils and Ancient Life

• Paleontologists- scientists who study fossils.

• Fossil Record- provides evidence about the

history of life on Earth. It also shows how

different groups of organisms, including species,

have changed over time.

How Fossils Form

• For a fossil to form, either

the remains of the

organism or some trace of

its presence must be

preserved.

Interpreting Fossil Evidence

• Paleontologists determine the age of fossils using

two techniques: relative dating and radioactive

dating:

• Relative Dating- the age of a fossil is determined by

comparing its placement with that of fossils in other

layers of rock.

• Radioactive Dating- scientists calculate the age of a

sample based on the amount of remaining radioactive

isotopes it contains.

Geologic Time Scale

• Geologic Time Scale-

divisions used to

represent evolutionary

time.

• Geologists divide time into

four major eras:

precambrian, the paleozoic,

the mesozoic, and the

cenozoic eras.

• Each era is subdivided into

periods

Geologic Time Scale

• Precambrian

• 88% of Earth’s history.

• Few multicellular fossils.

• Paleozoic

• Many vertebrates and invertebrates lived during the Paleozoic.

• Mesozoic

• “The Age of the Dinosaurs”

• Mammals began to evolve during the mesozoic.

• Cenozoic

• “The Age of the Mammals”

• The last 65 million years.

Exit Slip

• What are the four eras on the geologic time

scale?

• What is the difference between radioactive dating

and relative dating?

Warm Up Exercise

• On the half sheet of paper you picked up when

you came in, tell me what you did on your spring

break? Can you relate anything you did to

science in any way?

FlashBack

• What are the three parts of cell theory?

• What is transcription/translation?

Formation of Earth

• Geologic evidence shows that Earth is about 4.6

billion years old and was created over many

years.

• Earth was formed from cosmic debris which

compounded on one another over the course of

millions of years.

• Early Earth was extremely hot, and unsuitable for

life because of violent earthquakes and asteroid

impacts.

First Organic Molecules

• 1950s- Stanley Miller and Harold Urey tried to

simulate conditions of early Earth in the

laboratory.

• Filled flask with fluids and gases similar to those in

Earth’s early atmosphere. Passed electric sparks

through this mixture to simulate lightning. Their

experiments produced amino acids, the building blocks

of _______?________.

The Puzzle of Life’s Origins

• Insert figure 17.10

Free Oxygen

• Microfossils of unicellular organisms resembling

bacteria have been found in rocks more than 3.5

byo, which means that they must have evolved in

the absence of oxygen, because there was

little/no oxygen in Earth’s early atmosphere.

(Cyanobacteria)

• Photosynthetic organisms evolved later, which

created a rise in oxygen levels in the atmosphere.

This change likely caused some organisms to

become extinct, while others evolved more

efficient respiration mechanisms which utilized

oxygen.

The Endosymbiotic Theory

• One large prokaryotic cell, engulfed several other

smaller prokaryotic cells with specialized

functions. Together these cells lived symbiotically

and were interdependent on one another.

Collectively, they formed the first eukaryotic cell,

which went on to divide and give rise to other

eukaryotic cells.

The Endosymbiont Theory Plantsad

plant-like

protists

Warm Up Exercise

• What were the first type of cells on earth?

(prokaryotes/eukaryotes)

• How did early organisms breath?

(aerobic/anaerobic)

• Could humans have survived on early earth?

Why or why not?

• How old is Earth?

• What does the endosymbiotic theory say?

Patterns of Evolution

• Macroevolution- the large scale evolutionary

patterns and processes that occur over long

periods of time.

• Extinction

• More than 99% of all species that have ever lived are

now extinct.

• Several times in earth’s history, mass extinctions wiped

out entire ecosystems.

• Each mass extinction provides opportunities for

organisms that survive and often results in a burst of

evolution that produces many new species.

Patterns of Evolution

• Adaptive Radiation- when a single species or

small group of species evolves into several

different forms that live in different ways.

Patterns of Evolution

• Convergent Evolution- unrelated organisms

independently evolve similarities when adapting

to similar environments.

• Analogous Structures- structures which look and

function similarly but are made up of parts that do not

share a common evolutionary history.

Patterns of Evolution

• Coevolution- when two species evolve in

response to changes in each other.

Patterns of Evolution

• Punctuated Equilibrium- when long stable

periods are interrupted by brief periods of more

rapid change.

• Gradualism- the idea that biological change is slow and

steady. (supported by Darwin)

• Scientists suggest that most new species are produced

by periods of rapid change, because organisms evolve

rapidly to fill available niches.

Patterns of Evolution

• Developmental Genes and Body Plans

• Hox Genes- guide development of major body

structures in animals.

Exit Slip

• Darwin's species of finches were very similar but different in beak size and feeding habits. This is an example of

• convergent evolution.

• coevolution.

• adaptive radiation.

• stabilizing selection.

• A slow steady change in a particular line of descent is called

• coevolution.

• gradualism.

• punctuated equilibrium.

• convergent evolution.

• Master control genes are called

• hox genes.

• developmental genes.

• embryonic genes.

• regulatory genes.

Exit Slip

• Some evidence suggests that species do not change much over

long periods of time and then undergo relatively short periods of

rapid speciation. This kind of change is called

• coevolution.

• genetic equilibrium.

• adaptive radiation.

• punctuated equilibrium

• Fossil evidence shows that mass extinctions

• ended the existence of many species in a short period of time.

• occurred mainly when the dinosaurs disappeared.

• require an asteroid strike to occur.

• caused convergent evolution among animals.