Peppered Moths

Chapter 15

What is Evolution?• Evolution is…..– Change in a species over time– The process by which modern

organisms have descended from ancient organisms

– A theory• Well-supported testable

explanation (hypothesis) of phenomena that have occurred in the natural world

• Used to be called “transmutationism”

Charles Darwin• The major contributor to the theory• Born Feb. 12, 1809– Same day as Abe Lincoln!

• Theology major in college– Religion

• Competitor– Alfred Wallace– Published work on natural selection

before Darwin• Very Controversial character

Darwin’s Expedition• H.M.S. Beagle– Darwin took a trip around the

world on a ship• Like a vacation

– Went ashore when the ship ported

– Gathered animals and other evidence for his ideas

– Galapagos Islands• Main area of collection and

influence on his work• 1000 km west of South America

What did he find?• Patterns of diversity– Looked at why certain organisms were

found in only certain spots–Why did they survive there when

others didn’t?• He looked at Galapagos turtles and

finches in particular

Influences on Darwin’s Work• James Hutton

– Hypothesized that the earth was shaped slowly

– This went against the church btw• Charles Lyell– Principles of Geology– Explained how the earth could be changed

so drastically over time– Volcanoes, earthquakes, etc.– So… if the earth changes over time, can

animals?

Influences on Darwin’s Work• Jean-Baptiste Lamarck

– French naturalist studied animals’ ability to adapt– Tendency Toward Perfection• Changing to acquire adaptations to reach a perfect state

– Use and Disuse• If an organism doesn’t use a trait, then it’s lost over time• Ie our appendix and coccyx (tail bone)

– Inheritance of Acquired Traits• Traits gained can be passed on• Ie if I lift weights my whole life, then my children will

look like Arnold

Natural Selection“It is not the strongest of the species that survives,

nor the most intelligent that survives. It is the one that is the most adaptable to change.” -Charles Darwin

• Survival of the fittest– Fitness: the ability of an individual to survive and

reproduce in its specific environment

• Those individuals that possess adaptations that help them survive the best, will be the ones that reproduce and pass on their genes.

Evolution of PopulationsOccurs when there is a change in relative

frequency of alleles

Natural Selection and Species Fitness

• Overtime, natural selection results in changes in the inherited characteristics of a population.

• These changes increase a species fitness (survival rate)

Descent with Modification

• Each living species has descended with changes from other species over time

• Darwin’s idea

Endosymbiosis Theory

• Theory that during the evolution of the cell, one large bacteria cell engulfed another one that became the mitochondria – This is also how they

thought the chloroplast evolved as well

– They have their own DNA and a double membrane

Darwin’s Postulates1. Organisms differ; variation is

inherited2. Organisms produce more offspring

than survive3. Organisms compete for resources4. Organisms with advantages

survive to pass those advantages to their children

5. Species alive today are descended with modifications from common ancestors

Evidence of Evolution1. Fossil Record

2. Geographic Distribution of Living Species

3. Homologous Body structures

4. Similarities in Embryology

Fossil RecordFossil Record provides

evidence that living things have evolved

Fossils show the history of life on earth and how different groups of organisms have changed over time

Relative Dating• Can determine a fossil’s

relative age• Performed by estimating

fossil age compared with that of other fossils

• Drawbacks – provides no info about age in years– Index fossil: compares time

periods best over a short period of time and a wide geographic range

Absolute dating• Can determine the absolute

age in numbers• Is performed by radioactive

dating – based on the amount of remaining radioactive isotopes remain

• Drawbacks - part of the fossil is destroyed during the test

Trilobites: related to snowshoe crab

Carbon Dating

Geographic Distribution of Living Species

• How can animals be similar, but distinctly different?– The ones Darwin saw on the

Galapagos islands must have descended from a common ancestor

• Animals on different continents in similar environments have similar anatomies (body structures) and behaviors

Convergent Evolution• When species who are

not related evolve similarly due to a similar environmental pressures– Sugar glider and the

flying squirrel

More EvidenceHomologous Body

Structures–Structures that have

different mature forms but develop from the same embryonic tissuese.g. Wing of bat,

human arm, leg of turtle

Analogous Body Structures

• There appear to be many structures that are similar because of the function they carry out and in their external appearance. However, these structures differ internally. These species are NOT descended from a common ancestor. For example, wings of bat and butterfly are similar in appearance.

Vestigial Structures– traces of homologous organs in other species– Organ that serves no useful function

e.g. Appendix

Evidence ContinuedSimilarities in

Embryology– In their early stages of

development, chickens, turtles and rats look similar, providing evidence that they shared a common ancestry.

Speciation– Adaptive Radiation• The process in which multiple species adapt and change

(evolve) due to different environmental pressures from one common ancestor

How Does Speciation Occur?

• Geographic Isolation– Physical barrier separates a population

• Behavioral Isolation– Capable of breeding, but are separated by

courtship rituals or reproductive strategies• Temporal Isolation– Reproduce at different times

Coevolution• When organisms that are

ecologically close -- for example, predators and prey, or hosts and parasites -- influence each other's evolution, we say that coevolution is occurring – One species’ evolution is in response

to the other– One example is the bacteria living in

our stomachs. They have evolved along with us.

Human Skulls

Australopithecus Homo erectus Homo sapien

LigerResult of male lion and female tiger mating in

captivity. Offspring are infertile.

Tigon Result of male tiger and

female lion mating in captivity. Offspring are

infertile.

Extinction• 99% of all species that have ever lived are now

extinct