The Evidence for The Evidence for EvolutionEvolution

The ‘Evolution’ of The ‘Evolution’ of Evolutionary TheoryEvolutionary Theory

Darwin’s TheoryDarwin’s Theory

• Descent with modification descendants of earliest organisms spread

into various habitats over millions of years.– i.e. fur that blends with different environments,

protective camouflage• Natural Selection process by which individuals with inherited

characteristics well suited to the environment leave more offspring on average than do other individuals.

Within a Population of OrganismsWithin a Population of Organisms

Variation & Mutations

Adaptations Evolve

Struggle for Existence

Differential Reproductive Success

Overproduction

Evolution By Natural SelectionEvolution By Natural Selection

Observation 1Observation 1 Individuals in a species vary Individuals in a species vary in many ways.in many ways.

Observation 2Observation 2 Some of this variability can Some of this variability can be inherited.be inherited.

Observation 3Observation 3 Every generation produces Every generation produces far more offspring than can far more offspring than can survive and pass on their survive and pass on their variations.variations.

Observation 4Observation 4 Populations of species tend Populations of species tend to remain stable in size.to remain stable in size.

Evolution By Natural SelectionEvolution By Natural SelectionInference 1Inference 1 Members of the same species Members of the same species

compete with each other for compete with each other for survival.survival.

Inference 2Inference 2 Individuals with more favourable Individuals with more favourable variations are more likely to variations are more likely to survive and pass them on. Survival survive and pass them on. Survival is not random.is not random.

Inference 3Inference 3 As these individuals contribute As these individuals contribute proportionally more offspring to proportionally more offspring to succeeding generations, the succeeding generations, the favourable variations will become favourable variations will become more common. (This is natural more common. (This is natural selection.)selection.)

1. The Fossil Record1. The Fossil Record

A fossil is A fossil is any evidence any evidence of an organism that lived of an organism that lived long ago.long ago.

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

How Fossils FormHow Fossils Form Most are fossils found

in sedimentary rock. Formed when

exposure to the elements breaks down rocks into small particles.

Sediments pile up year after year, compressing the layers, and preserving the dead organism by turning it into rock.

How Fossils FormHow Fossils Form

Becoming A FossilBecoming A Fossil

Why Use Fossils?Why Use Fossils?

Scientists have used the fossil record Scientists have used the fossil record to construct a history of life on Earth.to construct a history of life on Earth.– Earth’s life forms appeared 3.5 billion Earth’s life forms appeared 3.5 billion

years agoyears ago– Fossil record is not complete, but pretty Fossil record is not complete, but pretty

good for general informationgood for general information Clear pattern of descentClear pattern of descent Transitional FormsTransitional Forms Distribution in time/spaceDistribution in time/space

Why Use Fossils?Why Use Fossils?

Why Use Fossils?Why Use Fossils?

Relative DatingRelative Dating Can determine a Can determine a

fossil’s relative agefossil’s relative age Performed by Performed by

estimating fossil estimating fossil age compared with age compared with that of other fossilsthat of other fossils

Drawbacks – Drawbacks – provides no info provides no info about age in yearsabout age in years

Why Use Fossils?Why Use Fossils?

Fossil Timeline - Permian ExtinctionFossil Timeline - Permian Extinction

Why Use Fossils?Why Use Fossils?

Absolute DatingAbsolute Dating Can determine the Can determine the

absolute age in absolute age in numbers.numbers.

Is performed by Is performed by radioactive dating – radioactive dating – based on the amount based on the amount of remaining of remaining radioactive isotopes radioactive isotopes remain.remain.

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

2. Radiometric Dating2. Radiometric Dating All living organisms contain carbon in two forms: the

isotopes carbon-12 (C-12), which has 12 neutrons in its nucleus, and carbon-14 (C-14), which has 14 neutrons and is radioactive.

When an organism dies, it no longer takes in carbon and its remaining radioactive C-14 decays into nitrogen-14 (N-14).

Over time, the ratio of C-12 to C-14 in the organism's remains changes, so by measuring this ratio you can calculate the time since death.

Every 5,730 years (1 half-life), 50 percent of the original amount of C-14 has decayed.

After about 50,000 years (8 half-lives), a sample has lost nearly all of its C-14 and can no longer be dated using this method.

Campbell, et.al., 2004

Radiometric DatingRadiometric Dating

Radiometric DatingRadiometric Dating

Radioactive Half-Life The radioactive half-life

for a given radioisotope is the time for half the radioactive nuclei in any sample to undergo radioactive decay.

After two half-lives, there will be one fourth the original sample, after three half-lives one eight the original sample, and so forth.

OPTIONAL: Short Video Clip on Carbon Dating

3. Age of the Earth3. Age of the Earth Along with determining the age of various fossils, Along with determining the age of various fossils,

the age of the Earth helped to support the age of the Earth helped to support evolutionary theory.evolutionary theory.

Development of Theory – Development of Theory – TimelineTimeline– Bishop UssherBishop Ussher– Hutton and Lyell Hutton and Lyell

argued that the earth is many millions of years old argued that the earth is many millions of years old b/cb/c

layers of rock take time to formlayers of rock take time to form processes such as volcanoes and earthquakes processes such as volcanoes and earthquakes

shaped the earth and still occur todayshaped the earth and still occur today Darwin would apply this notion of gradual change to Darwin would apply this notion of gradual change to

his theory of evolution.his theory of evolution.

3. Age of the Earth3. Age of the Earth

If science could assume that the If science could assume that the Earth was billions of years old (rather Earth was billions of years old (rather than a few thousand), gradual than a few thousand), gradual change in organisms over long change in organisms over long periods of time was possible.periods of time was possible.

‘‘Blip’ in evolutionary time:Blip’ in evolutionary time:– History of the Earth in 60 SecondsHistory of the Earth in 60 Seconds

4. Abiogenesis4. Abiogenesis Until the early 19th Until the early 19th

century people century people generally believed in generally believed in the ongoing the ongoing spontaneous spontaneous generation of life from generation of life from non-living matter — non-living matter — abiogenesis. abiogenesis.

Disproven by Redi and Disproven by Redi and PasteurPasteur

Made Darwin’s idea of Made Darwin’s idea of new forms evolving new forms evolving from old forms a better from old forms a better explanation for where explanation for where life comes from.life comes from.

5. Homology5. Homology Any similarity in Any similarity in

characteristics due characteristics due to shared ancestry.to shared ancestry.

Structures have Structures have different mature different mature forms but come forms but come from the same from the same embryonic tissue.embryonic tissue.

e.g. forelimbs in e.g. forelimbs in mammals (whale, mammals (whale, horse, bat, etc.)horse, bat, etc.)

HomologyHomology

Do these Do these forelimbs have forelimbs have the same the same function?function?

If not, why do If not, why do they have such they have such similar similar structure structure (same bones)?(same bones)?

Shared Shared ancestry!ancestry!

HomologyHomology

6. Analogy 6. Analogy Two structures in Two structures in

biology are said to be biology are said to be analogousanalogous if they if they perform the same or perform the same or similar function by a similar function by a similar mechanism but similar mechanism but evolved separately. evolved separately.

Convergent evolution.Convergent evolution. Different lineage, Different lineage,

similar evolutionary similar evolutionary strategy (i.e. wings for strategy (i.e. wings for flight)flight)

AnalogyAnalogy

Animals from different lineages or in different geographical locations develop similar adaptations for specific functions.

7. Vestigal Structures7. Vestigal Structures

• Traces of homologous organs can be found in other Traces of homologous organs can be found in other species.species.

• Organ or structure that serves no useful function.Organ or structure that serves no useful function.

e.g. Appendixe.g. Appendix

Whales have hipbones and traces of afemur. This indicates that they evolvedfrom ancestors that had hind legs.

Vestigal StructuresVestigal Structures• Coccyx• Body Hair• Darwin’s Point (ear)• Male Nipples• Wisdom Teeth

8. Embryology & Development8. Embryology & Development

In their early stages of development, chickens, turtles and rats look similar, providing evidence that they shared a common ancestry.

Embryology & DevelopmentEmbryology & Development

9. Geographic Distribution9. Geographic Distribution

• Similar animals in Similar animals in different locations different locations were the product of were the product of different lines of different lines of descentdescent

10. Biochemistry10. Biochemistry

Despite the diversity of living things on Earth, we share the common biochemical elements of heredity.

We all use the same building blocks of genetic material.

DNA and RNA

11. Adaptations11. Adaptations

• Lamarck (c. 1809) believed that organisms became Lamarck (c. 1809) believed that organisms became more complex over time.more complex over time.

• Acquired traits developed through use or disuse and Acquired traits developed through use or disuse and were passed on to future generations.were passed on to future generations.

AdaptationsAdaptations

Structural AdaptationsStructural Adaptations

1.1. Mimicry – organisms mimic another species Mimicry – organisms mimic another species to improve chances of survival.to improve chances of survival.

AdaptationsAdaptations

Structural AdaptationsStructural Adaptations

2.2. Camouflage – organisms blend in with their Camouflage – organisms blend in with their physical environment to avoid predation.physical environment to avoid predation.

AdaptationsAdaptations

Physiological AdaptationsPhysiological Adaptations

• e.g. antibiotic-e.g. antibiotic-resistant bacteriaresistant bacteria

• We will examine We will examine various types of various types of adaptations adaptations throughout this unit.throughout this unit.

Types of SelectionTypes of Selection

For NEXT class:

•We will have a short quiz on what we’ve explored so far.

•Please read Section 12.4 in the textbook (Forms of Selection) and be ready to discuss and apply the concepts next class.

Laws, Theories, & FactsLaws, Theories, & Facts

ScientificScientific– Law: a concise verbal or mathematical Law: a concise verbal or mathematical

statement of a relation that is always statement of a relation that is always under the same conditions. under the same conditions.

– Theory: a plausible general principle or Theory: a plausible general principle or body of principles offered to explain a body of principles offered to explain a phenomenon.phenomenon.

– Fact: an objective, verifiable Fact: an objective, verifiable observation. observation.

What Evolution Is Not…What Evolution Is Not…WHAT EVOLUTION IS NOTBiological Evolution...

1. is NOT a theory2. is NOT something one should believe in3. Is NOT concerned with the origin of life4. Is NOT just concerned with the origin of humans5. was NOT discovered or first explained by Charles Darwin6. is NOT the same thing as natural selection7. is NOT something that happened only in the past8. is NOT something that happens to individuals9. is NOT an accidental or random process10. does NOT have any evidence against it11. was NOT contrived to undermine religion12. does NOT deny the existence of God13. does NOT conflict with any religion

If these popular ideas about evolution are all wrong,then what IS evolution?

ReflectionReflection

Write a short reflection piece (about a page) in Write a short reflection piece (about a page) in which you express your opinion on the which you express your opinion on the differences between fact, theory, and law as differences between fact, theory, and law as they apply to the study of evolution.they apply to the study of evolution.

Into which of these categories do you think Into which of these categories do you think evolution falls. Give examples to support your evolution falls. Give examples to support your opinion.opinion.