EvolutionEvolution

Evidence of ChangeEvidence of Change

What is Evolution?What is Evolution?

The change in gene frequencies in a population over time

Evolution and Life’s DiversityEvolution and Life’s Diversity

• The idea that life has and is changing over time is not new.

• Evolution is the process by which modern organisms have descended from ancient organisms

Charles DarwinCharles Darwin(1809-1882)(1809-1882)

• Born in England• Attended medical school,

HATED IT, and dropped out to become a priest

• Liked to stuff birds instead of dissect humans

• Didn’t like grave robbing for bodies

• Boarded the H.M.S. Beagle for a 5 year UNPAID journey as a naturalist

Charles DarwinCharles Darwin• “Descent with

modification” from an ancestral species

• November 24th 1859

The Origin of SpeciesOccurrence of EvolutionDescent with Modification all organisms related through descent from some unknown ancestral population diverse modifications (adaptations) accumulated over time

Mechanism of EvolutionNatural Selection and Adaptation natural selection is the differential success in reproduction natural selection occurs from the interaction between the environment and the inherit variability in a population variations in a population arise by chance

Can selection actually cause substantial change in a population?

Journey of the Journey of the H.M.S. BeagleH.M.S. Beagle

Darwin’s Field Research• South American flora/fauna distinct from European flora/fauna

•S. American temperate species were more closely related to S. American tropical species than European temperate species

•S. American fossils were distinctly S. American

Tropical Rainforest of South America

Alfred Russel WallaceAlfred Russel Wallace(1823-1913)(1823-1913)

Presented a paper with identical ideas as Darwin on July 1, 1858 at the Linnaean Society meeting

Was a botanist who came up with virtually the same concept of natural selection more or less independently through his studies on the Malay archipelago. Darwin panicked because he was not ready with his book yet!

Diversity of LifeDiversity of Life

• Organisms come in a very wide variety of size, shape, and habit

• In one day, Darwin collected 68 kinds of beetles

• Estimates are about 10 million species exist today

• Estimates are that 99.9% of all species that have ever lived on earth are extinct!

Diversity of LifeDiversity of Life

• 2 questions:

• if the estimates are correct, – Where did they all come from?– Why did so many disappear?

FitnessFitness

• Darwin noticed most animals and plants seemed very well suited to do the things they do.

• The combination of physical traits and behaviors that helps an organism survive and reproduce Darwin called “Fitness”.

• How did the organisms develop structures that give them their fitness?

• Why are there such a variety of techniques for survival?

EvolutionEvolution

• Evolution is a long, slow process of change in a species over time.

• Common Descent – species that have descended from common ancestors

• Adaptation – a process that causes fitness (better able to survive and reproduce)

• Long legs and neck of giraffe are adaptations• Long legs and neck allow giraffes to eat leaves

too high for most grazing animals

Age of EarthAge of Earth

• Age of the Earth

• Evidence suggests

• earth is over 4 billion years old

• life has changed dramatically over time

• common descent

History of Earth in 1 Calendar YearHistory of Earth in 1 Calendar Year

• EventAge (approx) (Million years) Calendar date

• Earth formed 4,550 Jan. 1• Oldest rocks (sedimentary) 3,800 Mar. 1• 1st life forms (stromatolites) 3,500 Mar. 25• Oxygen in atmosphere (banded iron fm) 2,000 Jul. 24• 1st organized cells (eukaryotes) 1,000 Oct. 12• 1st multi-celled animals 680 Nov. 7• 1st fossils (hard skeletons) 570 Nov. 16• 1st vertibrate animals 450 Nov. 25• 1st land plants 430 Nov. 27• 1st fish 400 Nov. 29

History of Earth in 1 Calendar YearHistory of Earth in 1 Calendar Year

• 1st primates 80 Dec. 25• Extinction of the dinosaurs 65 Dec. 26 9:00 pm• Collision of India with Asia 65 Dec. 26 9:00 pm• Antarctica splits from Australia 53 Dec. 27• 1st horses 26 Dec. 29 10:00 pm• 1st apes 25 Dec. 29 midnight• Neanderthal man 0.042 Dec. 31 11:55:16 pm• Historical record (Sumeria) 0.005 Dec. 31 11:59:25• Establishment of U.S. 0.00022 Dec. 31 11:59:58.47• Life of a student (20 years)0.00002 Dec. 31 11:59:59.86

History of Earth in 1 Calendar YearHistory of Earth in 1 Calendar Year

• 1st amphibians 365 Dec. 2• 1st insects 350 Dec. 3• 1st reptiles 320 Dec. 6• 1st conifer trees 300 Dec. 7• Extinction of trilobites 285 Dec. 9• 1st mammals 200 Dec. 15• 1st dinosaurs 200 Dec. 15• Opening of the Proto-atlantic 200 Dec. 15• 1st birds 160 Dec. 19 5:00 am• Breakup of Gondwanaland 150 Dec. 19 11:00 pm• Opening of N. Atlantic 120 Dec. 22• Opening of S. Atlantic 92 Dec. 24

Evidence in StoneEvidence in Stone

• In the past, people believed• earth was only a few thousand years old• earth remained unchanged• humans rarely, if ever, witnessed the earth

changing• Scientists in the 18th and 19th Century

examined the earth and suggested the earth • is very old• changed slowly by forces such as weather

Evidence in StoneEvidence in Stone

• James Hutton (1788) proposed that rocks, mountains and valleys had been changed by rain, heat, cold, and activity of volcanoes

• 1830 (right before Darwin sailed) – Charles Lyell argued that scientists must always explain past events in terms of their observations

• While examining the earth and rocks, geologists began to discover fossils

• Fossils are the preserved remains of ancient organisms• Some resembled organisms still alive, some did not.

Geologic Time Scale: A Clock in the RocksGeologic Time Scale: A Clock in the Rocks

• Geologic Time Scale – a record in the rocks• certain layers appeared in the same vertical

order wherever they were found• Position of the layers relative to each other that

tells how old they are.• Lower is older• Relative Dating – technique to determine age of

fossils by comparing the layers they are found in• Could not tell actual age (only relative)

Radioactive DatingRadioactive Dating

• Middle of this century, our understanding of radioactivity gave scientists a tool to determine actual age of rocks

• Radioactive elements break down or decay into nonradioactive elements at a constant rate

• Half life – length of time required for half of the element to decay

• 1 half life - ½ radioactive element broken down• 2 half lives – ¾ radioactive element broken down• 3 half lives – 7/8 radioactive element broken down

Radioactive DatingRadioactive Dating

• Each element has a different half life • Potassium – 40 has a half life of 1.3 billion

years• In one half life of P-40, one half of the

atoms decay to argon –40.• Uranium 238 has a half life of 4.5 billion

years – during that time, ½ of the atoms become lead-206

• 13-8 – half lives of radioactive elements

Absolute DatingAbsolute Dating

• Using this information, scientists can date very accurately. This is called absolute dating

• Using this, scientists have divided the earth’s history into units called eras

• Eras are divided into periods• Periods are divided into epochs• Based on this information, scientists have

determined that the earth is 4.5 billion years old.

The Fossil RecordThe Fossil Record

• Animals and plants that are preserved by natural means

• Can be Trapped in tree sap - amber

• Trapped in sedimentary rock

• Minerals replace the organic components (usually shell or bone)

The Fossil RecordThe Fossil Record

• Most in sedimentary rock

• Sand and small rocks settle down and compact making layer upon layer

• Older on bottom

• Like a jigsaw puzzle

• Not as complete as we would like

The Fossil RecordThe Fossil Record

• For every organism that leaves a fossil, many do not leave anything

• Also depends on where the organisms lived. If they lived in the mountains, chances are smaller that they would leave a fossil

• Finding fossils can be difficult, but nature sometimes helps – weather or water may erode newer layers exposing fossils

• Some fossils are not as well preserved as others. • Some – we can see microscopic detail, others are not as

clear

Half LivesHalf Lives

Isotope Pair Half-life (yrs) Useful Range (yrs)

Carbon-14 to Nitrogen-14

5730 60,000

Uranium-235 to Lead-207

700 million Over 500 000

Potassium-40 to Argon-40

1.25 billion Over 500 000

Uranium-238 to Lead-206

4.5 billion Over 100 million

Half LivesHalf Lives

• Sometimes use different materials, half life of Potassium-40 is too long to use for some living things

FossilsFossils

• Paleontologists – scientists who study fossils

• Collect “fossil record” that represents preserved collective history of Earth’s organisms

• Horse evolution – page 281 13-15

FossilsFossils

• Location of fossils shows major changes in earth climate and geography

• Shark teeth found in Arizona – Must have been covered with seas

• Giant fossil ferns in Canada – must have been warmer, tropical climate

• Changes followed changes on earth

• Paleontology - Study of Fossils Fossil - preserved evidence of past life a. Relative dating

b. Radioactive dating

                                                                                                                 

                                                          

• HOMOLOGY is a characteristic shared by

two species (or other taxa) that is similar because of common ancestry.

• morphological homology – species placed in the same taxonomic category show anatomical similarities.

• ontogenetic homology - species placed in the same taxonomic category show developmental (embryological) similarities.

• molecular homology - species placed in the same taxonomic category show similarities in DNA and RNA.

MORPHOLOGICAL MORPHOLOGICAL HOMOLOGYHOMOLOGY

• Structures derived from a common ancestral structure are called:

HOMOLOGOUS STRUCTURES

Ontogenetic HomologyOntogenetic Homology The human embryo has gills, a post-anal tail,

webbing between the toes & fingers, & spends its entire time floating and developing in amniotic fluid has similar salt concentration as ocean water

Figure 22.15

Pharyngealpouches

Post-analtail

Chick embryo Human embryo

MORPHOLOGICAL MORPHOLOGICAL HOMOLOGYHOMOLOGY

• A structure that serves the same function in two taxa, but is NOT derived from a common ancestral structure is said to be an

ANALOGOUS STRUCTURE

Sugarglider

AUSTRALIA

NORTHAMERICA

Flyingsquirrel

•Some similar mammals that have adapted to similar environments

–Have evolved independently from different ancestors

Examples of Analogous Examples of Analogous structures:structures:

• wings of bat, bird, and butterfly

• walking limbs of insects and vertebrates

• cranium of vertebrates and exoskeleton head of insects

• 4 chambered heart in birds & mammals

Molecular HomologyMolecular Homology

                                                                                                                 

                                                          

VestigialVestigial StructuresStructures

• Have marginal, if any use to the organisms in which they occur.

• EXAMPLES:• femurs in pythonid snakes and pelvis in

cetaceans (whales)• appendix in humans • coccyx in great apes