Evolution – A Theory

• In science, a theory is a testable, well supported scientific explanation of events in the natural world.

• A theory is a scientific statement which is still not absolutely proven to be true.

• A scientific theory may ultimately be proven to be true or false.

The Origin of Life

• Life on Earth began about 3.5 billion years ago.

• The Earth was covered in a hot, thin soup of water and organic materials.

• Over time, the molecules became more complex and could run metabolic processes.

• This is how molecules such as nucleotides, proteins and ATP were formed.

The Origin of Life: The Heterotroph Hypothesis

The Earth’s atmosphere was different.

FOSSILS

Fossils Form In Sedimentary Rock

-over time, pieces of earth erode and are worn away by wind and water. Layers of eroded earth are deposited on top of each layer. These layers press down until the bottom layers turn into rock.

Preservation inVolacanic Ash- Eruption of Vesuvius in 80 BC

Two of the creatures that left their footprints across this landscape of volcanic ash, 3.6 million years ago, were members of the early human species Australopithecus afarensis,, walking along side each other.

Refrigeration of Soft Parts

This frozen baby wooly mammoth probably lived 22,000 years ago. It was found in Siberia in 1997.

Ice Man

(Austria)

Insects inAmber

Transitional Series

Humans walked more upright,developed a distinct neck and reduced brow ridge.

Transitional Series

Archaeopteryx

Intermediate Forms

Monotremes

Intermediate Forms

-anteaters, duck-billed platypus-egg laying mammals-skulls almost birdlike-no teeth as adults

Intermediate Forms

Vestigial Structures

appendix

vestigial leg bones

Vestigal structures

• The vestigial wings of this flightless cormorant are too small to allow it to fly.

Comparison of Proteins: Hemoglobin Comparison

Species Amino Acid Differences

Gorilla 1

Rhesus monkey 8

Mouse 27

Chicken 45

Frog 67

Lamprey 125

Evidence from Embryology

Lamarck: Theory of Use and Disuse

appendix

The selective use or disuse of organs leads to acquiring or losing certain traits during an organism’s lifetime.

These traits can then be passed onto offspring. Over time, there is a change in the species.This theory is not true!

Lamarck’s Theory of Acquired Characteristics

tail tail

Xtail cut off tail cut off

tailWeismann

Theory ofAcquiredCharacteristicsDisproved

Darwin

Voyage of the Beagle1859- On the Origin of Species by Means of Natural Selection is written.

Galapagos Tortoises

Marine Iguana

FlightlessCormorant

Darwin found different

characteristics on different islands- each well suited to their environment.

Theory of Natural Selection

•Species are not perfect or unchanging.•There is natural variation among offspring.•This variation among offspring is inherited.•There is overpopulation- this leads to •competition for resources-a struggle for •existence. • This leads to survival of the fittest.

“Evolution by Natural Selection”

• Fitness is a result of an organism’s adaptations: inherited traits that increase

• an organism’s chance of survival.• Those organisms that are the most fit • survive ► reproduce ►pass on their • traits to their offspring.• Examples: porcupine’s sharp quills, faster

birds, animals that hunt in packs

“Evolution by Natural Selection”

•Variations occur – descent with •modification. Over time, natural selection•produces organisms with different •structures to suit their environment.•Changes in Gene Frequency•Changes in Species

Sources of Variations

•mutations•crossing over during meiosis•recombination of genes at fertilization

Changes in Gene Frequency as a Result of:

•geographic isolation•reproductive isolation•environmental changes

Geographic Isolationat the Grand Canyon

Behavioral Isolation

Differences in Mating Calls

The Founder Principle• A small number of people have

many descendants surviving after a number of generations.

• High frequencies of specific genetic traits are inherited from a few common ancestors.

• Example: Amish people in Lancaster, Pennsylvania are descended from a few dozen people in Germany. There is a high incidence of a rare fatal genetic disorder (microcephaly).

Bottleneck EffectA catastrophe occurs during which

most individuals of a species die, without passing on their genes.

This causes a reduction in the genetic

diversity of the species.

Changes in Species Resulting From:

•resistance (insects, bacteria)•industrial melanism (peppered moths)

Industrial Melanism- Kettlewell’s moths

European peppered moths have 2 color variations. The darker moths (with more melanin) were rare until industrial pollution in the 1850s, when tree trunks darkened due to soot.

Convergent Evolution

• The development of similar appearance, structures, or behavior in unrelated species/ populations because organisms live in similar habitats.

• Example: the wings of a bird and the wings of an insect; the body plan of a shark and a dolphin.

Convergent Evolution

Convergent Evolution

Divergent Evolution

A single group of organisms splits into groups that evolve in different directions.

Species – a group of organisms that can breed together under natural conditions to produce fertile offspring.

X

horse

infertile mule -

donkey

X

- not a species

Father = tigerMother = lion

Father =lionMother =tiger

Tiglon Liger

sterile and do not mate under natural conditions- not a species