The Theory of Evolution

Vocabulary

Evolution = process by which modern organisms have descended from ancient organisms. A change in populations over long periods of time.

Scientific Theory = well-supported, testable explanation of phenomena that have occurred in the natural world.

Charles Darwin**In 1831, Darwin set sail from England aboard the H.M.S. Beagle for a voyage around the world.

**During his travels, Darwin made numerous observations and collected evidence that led him to propose a hypothesis about the way life changes over time. (natural selection)

Natural Selection also known as: Survival of the Fittest

Process by which individuals who are better adapted for their environment survive and reproduce successfully.

In the Galapagos Darwin notices that there were variations among members of the same species.

Example: Finches, Giant Tortoise

Three species of tortoises each inhabit a different island in the Galápagos

Testudo abingdonii, inhabits the Pinta island and has a longer neck to reach vegetation

Pinta IslandIntermediate shell

Pinta

Isabela IslandDome-shaped shell

Hood IslandSaddle-backed shell

HoodFloreana

Santa Fe

Santa Cruz

James

Marchena

Fernandina

Isabela

Tower

Fitness: the ability for an organism to survive and reproduce in its environment. It’s a result of adaptation.

Adaptation: any inherited characteristic that increases an organism’s chances for survival.

Hummingbirds have adapted to their environment in two ways:1.Very fast flight to keep them steady.2.Long beak and tongue to reach into flowers and extract nectar.

Peppered MothsThe evolution of the peppered moth over the last two hundred years has been studied in detail. Originally, the vast majority of peppered moths had light coloration, which effectively camouflaged them against the light-colored trees and lichens upon which they rested. However, due to widespread pollution during the Industrial Revolution in England, many of the lichens died out, and the trees which peppered moths rested on became blackened by soot, causing most of the light-colored moths, to die off due to predation

The Peppered Moth Scenario is an example of ______.

a. Transcription

b. Natural Selection

c. Artificial Selection

d. Translation

1

Mosquito Count

0

10,000

20,000

30,000

40,000

50,000

60,000

1 3 5 7 9 11 13 15 17

Weekly Spraying

Mosq

uit

os

Mosquitos

2 4 6 8 10 12 14 16 18

A small Texas town recorded the above mosquito data every week for a 5-month period of time. During this time insecticide was sprayed to try and reduce the large number of mosquitoes.

What is the best explanation for the decreased effectiveness of the insecticide over time?

A Mosquitoes that were resistant to the insecticide lived and produced offspring.

B The insecticide was sprayed only once.

C The insecticide harmed the mosquito’s DNA causing mutations that prevented reproduction.

D The temperature decreased the effectiveness of the insecticide.

Evidence of evolution.

DARWIN INFLUENCED BY THE STUDIES OF VARIOUS PEOPLE SUCH AS:

LYELL AND HUTTON - Geologists who proposed that the earth was millions of years old and that geological events such as volcanic eruptions and earthquakes have changed and shaped the earth over long periods of time and continue to do so.

THOMAS MALTHUS – An Economist who predicted that if populations continued to grow out of control, there would be less resources like food, water and space to sustain the populations.

Jean Baptiste Lamarck – A French naturalist who was one of the first to recognize that organisms change over time but proposed that traits were acquired through use or disuse such as the long neck of the giraffes.

Evidence that living things have been evolving for millions of years includes:

The fossil recordSome of the fossils resembled organisms that

were still alive. Others looked completely unlike any creature he

had ever seen.

Homologous, analogous, and vestigial structuresEmbryologyGeographic distribution of living thingsBiochemistry

Water carries small rock particles to lakes and seas.

Dead organisms are buried by layers of sediment, which forms new rock.

The preserved remains may later be discovered and studied.

What are fossils? Remains of once living organismsLike the hard parts of organisms (i.e. bones), impressions, or casts.

Portrayed by remains of ancient life forms.

When fossils are discovered they can be added to the fossil record based on age and similarities.

Found mainly in Sedimentary Rock

Similar in structure but functions differentlyExamples: flying, swimming, grasping etc.

Structures that have a similar function, but different structures.

Example: Butterfly and bird both use their wings for flying, but wings are structured differently, one has bones, one has network of veins.

Structures that serve no useful purpose in an organism.

In whales, there is a vestigial pelvis and femur. In horses, there is a vestigial toe. In snakes, there are vestigial hips

Can you name any vestigial structures in humans?

Similarities in EmbryologySimilarities in Embryology

In their early stages In their early stages of of

development, development, chickens, ,

turtles and rats look turtles and rats look similar, providing similar, providing

evidenceevidence that they shared a that they shared a

common ancestor.

Closely related species share common genetic base sequences

Biochemistry: DNA and Proteins

Based on modern knowledge of genetics, we now know that natural selection is dependent on genetic variation within the gene pool.

Gene Pool: consists of all the genes including all the different alleles that are present in a population.

A population is a group of individuals that inhabit the same area.

A species is a group of similar organisms that can breed and produce fertile offspring.

Geographic Isolation:When two populations of a species

becomes separated by geographic barriers such as rivers or mountain ranges resulting in the formation of 2 separate gene pools.

Ex: Abert Squirrels vs. Kaibab Squirrels.

a change in allele frequencies that occur in small populations. These changes are associated with random events .founder effect

small group splinters off & starts a new colonybottleneck

some factor (disaster) reduces population to small number & then population recovers & expands again

diverse population “catastrophic event” (hunting, earthquake, volcanic eruption, etc. small % of the original population remains & repopulates less diverse population

Bottleneck EffectBottleneck Effect

When large population is drastically reduced by a disasterfamine, natural disaster, loss of habitat…loss of variation by chance event

alleles lost from gene poolnot due to fitness

narrows the gene pool

All cheetahs share a small number of allelesless than 1% diversityas if all cheetahs are

identical twins2 bottlenecks

10,000 years agoIce Age

last 100 yearspoaching & loss of habitat

Small population gets separated by chance (storm, earthquake, etc.)

Develop different adaptations over many generations

If they come in contact later, they are too different to interbreed

Ex. Galapagos finches fly to nearby island

When a new population is started by only a few individualssome rare alleles may be at high frequency;

others may be missing

skew the gene pool of new populationhuman populations that

started from small group of colonists

example: colonization of New World

Genetic Flow: the transfer of genes or alleles from one population to another.

Movement of individuals & alleles in & out of populationsseed & pollen distribution by

wind & insectmigration of animals

sub-populations may have different allele frequencies

causes genetic mixing across regions

reduce differences between populations

Gene flow in human populations is increasing todaytransferring alleles

between populations

Are we moving towards a blended world?Are we moving towards a blended world?