Chapters 16 & 17

Evolution of Populations and The History of Life

Evolution of Populations

• EQ: How can populations evolve to form new species?– How do genes make evolution possible?– What causes a population’s gene pool to

change?

-- How do new species form?

Background and Review:

How are evolution and genetics related?

Jean-Baptiste Lamarck

He was the first to propose how organisms could change over time.

Theory of Acquired Characteristics

• Theory that organisms’ selective use and disuse of organs led to acquiring or losing certain traits in their lifetime.

• These traits could then be passed on to their offspring

• Ex) giraffe stretching to get leaves = neck gets longer over time….pass longer neck on to offspring (incorrect)

Darwin

Proposed the mechanism of NATURAL SELECTION to explain the observable

patterns of evolution

DarwinOn what concept was this work based?

Observations

• Members of a population often vary greatly in their triats

• Traits are inherited from parents to offspring

• All species are capable of producing more offspring that their environment can support

DarwinOn what concept was this work based?

Inferences

• Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals

• This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

Genetics & Evolution• Scientists discovered that heritable traits are

determined by DNA (genes on chromosomes).

• Later they realized that changes in the DNA (mutations) and gene recombination through sexual reproduction results in variations; thus, further relating Darwin and Mendel’s original work.

 

Evolution acts on ______________________ not on individuals.

 

Example: Black lizards are able to absorb more heat on cold days. The extra heat allows

them to move more quickly on cold days which makes them better able to

avoid predators. The allele for black body would increases an individuals

fitness and they would leave more offspring that other lizards. The relative

frequency of the allele for black body could, therefore increase.

How do genes make evolution possible

Two main sources of genetic variation

1. Mutations—change in genes (DNA sequence) or chromosomes

2. Gene recombination—mixing of genes that result from:

A. meiosis

B. sexual reproduction

What causes a population’s gene pool to change?

Gene Pool

The combined genetic information of all the members of a particular population

Selection processesStabilizing-natural selection in which intermediate phenotypes survive more

successfully than do extreme phenotypes

Selection processesDirectional- natural selection in which individuals at one end of the phenotypic range survive more successfully than do

other individuals.

Selection processes Disruptive-natural selection in which

individuals on both extremes of a phenotypic range survive more successfully than do individuals with intermediate phenotypes

Selection Curves

How do new species form?

Species

• A group of similar organisms that can breed and produce fertile offspring

Genetic Drift

Random change in allele frequencies that occur in small populations

SpeciationFormation of a new species through

reproductive isolation

Example: Galapagos Island finches and tortoises

Darwin’s Galapagos Island finches

Three types of reproductive isolation

1. Behavioral isolation (sounds or display rituals)

2. Temporal isolation (nocturnal vs. diurnal)

3. Geographical isolation (separated by oceans or mountain ranges)

If one of the Earth’s plates moves 1.9 cm a yr., in 1 million years it would move 12 miles

Geographical Isolation

Allopatric SpeciationGr. other + fatherland

The formation of new species in populations that are geographically isolated.

Ex: mountains, canyons, or oceans

Sympatric SpeciationGr. together + fatherland

Formation of a new species in populations that live in the same geographic area.

Behavior

A way an organism reacts to changes in its internal condition or external

environment

Migration

Periodic movement and return of animals from one place to another. Organisms that migrate have an advantage over one’s that

do not.

Migration

• Example: • 1. Monarch Butterfly

• http://video.pbs.org/video/1063682334 (2min)

• 2. Salmon • To the left:

• Pink • salmon • moving

• upstream.

CourtshipType of behavior in which an animal sends out stimuli in order to attract a member of

the opposite sex.

30 Minute Mark: http://www.pbs.org/wnet/nature/episodes/what-males-will-do/video-full-

episode/5374/

http://www.pbs.org/wnet/nature/video/what-males-will-do-video-spider-courtship-dance/956/

Social Behavior

The interaction of members with their own species in a way to increase the fitness of

all members.

Ex: packs, colonies, hives, troops

Chapter 17 The History of Life

– How do scientists use fossils to study Earth’s history?

– What are some patterns in which evolution has occurred?

– How fast does evolution take place?

EQ: How do fossils help biologists understand the history of life on Earth:

Earth’s Early Atmosphere

• Over time photosynthetic bacteria became common in the sea which started adding oxygen to the atmosphere

• Next, oxygen gas started accumulating in the atmosphere which decreased the hydrogen sulfide and methane and eliminating most anaerobic organism but increased aerobic organisms

• The ozone layer started to form to provide protection from ultraviolet rays

• Some organisms evolved ways of using oxygen for respiration and greater energy production

• With more energy available, eukaryotes evolved in the sea and then on land

• The eukaryotic cells aggregated into multicellular organisms and the evolution of the diversity of life was well on its way

Miller and Urey ExperimentCarl Sagan Explains Miller-Urey Experiment:

http://www.youtube.com/watch?v=79o6xzMfzKg

Miller-Urey Experiment Animation:http://www.youtube.com/watch?v=iahBQolXQH8

**Mixtures of the organic compunds necessary for life could have arisen from simpler compounds on present on a primitive Earth.

**Found that life arose from non-life. Is this true?

Fossil

• Preserved remains of ancient organisms

• http://www.neok12.com/php/watch.php?v=zX076e0e6d5a7b775b0d7a41&t=Fossils

Fossil Record

Information about past life that has been obtained from fossils

1. Most organisms that have ever lived are now extinct

2. fossils occur in a particular order in the rock layer

3. groups of organisms have changed over time

Extinct

A species that has completely died out

Extant

Species that still survive

Where do most fossils form?

Most fossils form in sedimentary rock as weight compresses layers

of sediment in bodies of water

• Not all parts of animals become fossilized.

• Fossilization activity

http://www.ucmp.berkeley.edu/education/explorations/tours/fossil/5to8/Intro.html

What are some patterns in which evolution has

occurred?

Mass ExtinctionMany types of living things become extinct in a

short period of time

Ex: Dinosaurs

Asteroid hitting Earth at Chicxulub Mexico on the Yucatan peninsula

?????

http://www.neok12.com/php/watch.php?v=zX060c4178075b5f7f7e6663&t=Prehistoric

-Animals 

How fast does evolution take place?

Gradualism

A model of evolution which theorizes that most speciation is slow, uniform and gradual.

Punctuated Equilibrium

Long period in which a species undergoes little to no change, interrupted by relatively brief periods of sudden change

Catastrophism

The principle that events in the past occurred suddenly and were caused by

different mechanisms than those operating today