Evolution and the History of Life MLK Fall 2005 M.Elizabeth.

Evolution and the History Evolution and the History of Lifeof Life

MLKMLKFall 2005Fall 2005

M.ElizabethM.Elizabethwww.marric.us/teachingwww.marric.us/teaching

• Chapter 8.1 Change Over Time– Differences Among Organisms– Do Species Change Over Time– Evidence of Evolution: The Fossil Record

• Fossils• Reading the Fossil Record• Gaps in the Fossil Record• Vestigial Structures

– Case Study: Evolution of the Whale– Evidence of Evolution: Comparing

Organisms• Comparing Skeletal Structures• Comparing DNA from Different Species• Comparing Embryonic Structures

Changes Over TimeChanges Over Time• Differences between species relate to

adaptations.• Adaptations – a hereditary characteristic

(attribute) that helps an organism survive and reproduce in its environment. – Physical adaptations are heredity. Which

means that the organism has no choice about the characteristics.

– Emotional, cultural, and behavioral adaptations are choices that humans can make.

•

It’s all about SpeciesIt’s all about Species• What is a Species?

– A population of organisms that can mate with one another produces fertile offspring.• Example: Horses, Donkeys, and Mules

– Breeding a male donkey to a female horse results in a mule;

– Breeding a male horse to a female donkey produces a hinny

+ =Sterile Mule

Horses and Donkeys are separate species

Do Species Change Over TimeDo Species Change Over TimeThe Earth is very old – 4.6 Billion Years• The Earth was formed approx. 4.6 bya

– The oldest rock is 3.5 Billion years

• Fossil evidence suggests that species have changed over time because younger fossils are different, yet similar to older fossils.

EvolutionEvolution• Evolution is the process by which

populations of organisms acquire and pass on unique traits from generation to generation, affecting the overall makeup of the population and potentially leading to new species.

Four distinct mechanisms generate Four distinct mechanisms generate evolution (evolution (change in allelic frequency in change in allelic frequency in populations over time)populations over time)::

1. mutation 2. gene flow 3. genetic drift 4. selection (natural and

“artificial”)

Gene flow = movement of alleles from one Gene flow = movement of alleles from one population to another, which may change the population to another, which may change the

allele frequenciesallele frequencies • Gene flow can happen in several ways; in

reality, usually a combination of them – individuals leave a population, taking their

alleles with them – individuals join a population, introducing new

alleles (or more copies of ones already present)

– individuals in the population mate with outsiders, but the offspring stay in the population

• this introduces new alleles (or additional copies of ones already present), because half of the offspring's alleles are from the outsider

• Gene flow essentially moves alleles between populations – this tends to make neighboring

populations similar to each other – because they exchange alleles and

individuals in each have ancestors from the other

– gene flow can take a mutation in one population and spread it throughout the world

Gene FlowGene Flow• the more migration or interbreeding

occurs between two population, the more rapidly they become similar

• gene flow is important because it explains how a species like humans can be essentially the same all around the world

Genetic DriftGenetic Drift• Genetic drift = change in allele

frequencies due to chance • how it works

– in any random process, like flipping a coin, we can predict the odds of any given outcome, but we can't predict which specific outcome will occur in any given case

• Genetic Drift has a greater effect on smaller populations than larger populations.

• In large populations, drift will not have much effect

• just as when you flip a coin 1000 times, you expect to get fairly close to 500 heads

• but the smaller the population, the more this random sampling error will change allele frequencies every generation

• just as when you flip a coin only 4 times, you are not surprised at all to get 75% heads, or even 100% heads

Geologic Time NotationsGeologic Time Notations

ya – Years Ago

mya – Million of years ago

bya – Billion years ago

Precambrian Paleozoic ERAMesozoic ERA Cenozoic

ERA

Era word rootsEra word roots• Geologist use the clues in some of these

words. • For example:

– zoic refers to animal life– paleo means ancient– meso means middle,– ceno means recent.

• So the relative order of the three youngest eras, first Paleoozoic, then Mesozoic, then Cenoozoic, is straightforward.

Evidence of Evolution: The Fossil Evidence of Evolution: The Fossil RecordRecord

• Fossils• Reading the Fossil Record• Gaps in the Fossil Record• Vestigial Structures

FossilsFossils• Are found in the

earth’s crust – the very uppermost part of the earth that is exposed to the surface or lying immediately below the oceans.

The Best Crust for FossilsThe Best Crust for Fossils• Sedimentary Rocks are the best crust

for fossil formations;

Example: The Grand Canyon. Strata = Layers of sediment so its called sedimentary rock

Rocks contain clues to the Earth’s past.Rocks contain clues to the Earth’s past.

What are FossilsWhat are Fossils• Fossils are the mineralized remains of

animals or plants or other traces such as footprints.

• All of the fossils and their placement in rock formations and sedimentary layers (strata) is known as the fossil record.

• The study of fossils is called paleontology.

What kind of rock is this?What kind of rock is this?

Sedimentary RockSedimentary Rock

Law of Superposition:Youngest on Law of Superposition:Youngest on TopTop

• An undeformed sedimentary rock layer is older than the layers above it and younger than the layers below it

A

B

C

D

Law of SuperpositionLaw of Superposition

A

B

C

D

• In terms of Relative Age• Rock Layer B must be younger than Rock Layer A• but

Rock Layer B is older than Rock Layers C and D.

• Once the order of formation is known, a RELATIVE AGE can be determined for each rock layer

http://pubs.usgs.gov/gip/fossils/

Gaps in the Fossil RecordGaps in the Fossil Record• Occur because specific conditions are needed

for fossils to form• Organisms with hard body parts (skeletons) are

more likely to form fossils than organisms with soft body parts. Basic to this is the organisms cannot be eaten before fossilization

– Find shells and bones• Fossils form best without oxygen – why peat bogs

and tar pits have great fossils. Burial by sediments reduce oxygen exposure.

• Freezing also allows fossil formation – Mammoth that Japanese scientists are trying to clone from DNA extracted from frozen Mammoth fossil.

• Fossils once formed must not be destroyed.

Sea shells embedded in Sea shells embedded in marine rock near Santa marine rock near Santa

CruzCruz

Ammonites near Ammonites near ReddingRedding

Human RemainsHuman Remains

Vestigial StructuresVestigial Structures• Mammals are warm blooded vertebrates• Vestigial structures are organs that have

no apparent function.• Examples:

– Human appendix – narrow tube attached to the large intestines

– Chimpanzee, gorilla, and orangutan appendix is functional and used to help digest tough plant material

Appendix

Whale evolutionWhale evolution(terrestrial to aquatic in ~ 8 Myr)(terrestrial to aquatic in ~ 8 Myr)

8 million years total

PBS Whale EvolutionPBS Whale Evolution

http://www.pbs.org/wgbh/evolution/library/03/4/l_034_05.html

One structural remnant (remaining part) of this evolutionary process are hind limb bones. These bones are called vestigial structures.

Evidence of Evolution: Evidence of Evolution: Comparing OrganismsComparing Organisms

• Comparing Skeletal Structures• Comparing DNA from Different Species• Comparing Embryonic Structures

Comparing Skeletal StructuresComparing Skeletal Structures• Homologous Structures

– Having similar origins and anatomical patterns

– Examples – bird wings, human arms, whale flippers, bat wings, cat legs.

HomoHomologous Structureslogous Structures

Analogous StructuresAnalogous Structures• Analogous

structures do the same thing – similar function, but different anatomy.– Wings (butterfly

external skeleton, bat internal skeleton• Analogous structures:

wing of an insect, bird, bat and pterosaur

Comparing DNA from Different Comparing DNA from Different SpeciesSpecies

• The actual molecular characteristics of DNA is measured and compared to other organisms.

• There are four different nucleotides in DNA (Adenine, Guanine, Cytosine, and Thymine).

• Gene sequencing – sections of DNA are sequenced for the order of nucleotide bases (ATCG or ATGC or ACTG, etc).

What We've Learned So FarWhat We've Learned So Far• By the Numbers: What Does the Draft

Human Genome Sequence Tell Us? • The human genome contains 3164.7 million

chemical nucleotide bases (A, C, T, and G). • The average gene consists of 3000 bases,

but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases.

• The total number of genes is estimated at 30,000 —much lower than previous estimates of 80,000 to 140,000.

• Almost all (99.9%) nucleotide bases are exactly the same in all people.

• The functions are unknown for over 50% of discovered genes.

Looking for RelatednessLooking for Relatedness

Crime Solving:The COmbined DNA Index System, CODIS, blends computer and DNA technologies into a tool for fighting violent crime.

Comparing Embryonic StructuresComparing Embryonic Structures• Ontogeny: Development of the

Individual from conception to death.

• Phylogeny: Development of the Species.

• Vertebrate organisms (those having a backbone) have similar stages of life as an embryo

Open Court Open Court Publishing Publishing CompanyCompany

Chapter 8.2 How Does Evolution Chapter 8.2 How Does Evolution OccurOccur

• Charles Darwin– Darwin’s Excellent Adventure– Darwin’s Finches– Darwin Does Some Thinking– Darwin Learned from Farmers and Animal

and Plant Breeders– Darwin Learned from Geologists– Darwin Learned from the Work of Thomas

Malthaus– Natural Selection– More Evidence of Evolution (DNA Mutation)

Darwin’s Excellent AdventureDarwin’s Excellent Adventure• HMS Beagle – Galapagos Island Travels• Galapagos Islands are part of the

country of Ecuador though the islands are about 1,000 kilometers west of the continent of South America in the Pacific Ocean. There are 19 volcanic islands with a land area of 8,000 km2 in an area of the Pacific Ocean over 60,000 km2About Darwinhttp://www.aboutdarwin.com/timeline/time_01.html

Darwin’s FinchesDarwin’s Finches

DiversityDiversity• Darwin saw finches that were very

different from each other as he traveled to the various islands of the Galapagos.

• Because of their physiological differences (beak shapes), the finches had very different diets

The diversity of life…The diversity of life…Although there is unity in life there is also a great deal of diversity!

Estimates of Diversity:

~1.7 million cataloged species

50,000 vertebrates

260,000 species of plants

750,000 species of insects

Total diversity 5-30 million species !

Darwin Does Some ThinkingDarwin Does Some Thinking• Darwin wonders how did the finches

become so different. He thought maybe there was a storm that separated the original population resulting in geographic isolation (one of the ways that speciation can occur)

Darwin Learned from Farmers and Darwin Learned from Farmers and Animal and Plant BreedersAnimal and Plant Breeders

• Darwin was very familiar with artificial selection or better known as selective breeding.

• Certain traits are determined by the breeder to be favorable. If only those organisms with the favorable traits are breed then the trait will occur more often in the population. By isolated certain individuals the differences can grow.

All from an ancestral dog

Darwin Learned from GeologistsDarwin Learned from Geologists

• Darwin learned from Charles Lyell that the Earth was formed over a long period of time by natural process.

• This idea of geologic time (really really long time ago) helped Darwin to more seriously consider natural processes for changing populations.

Darwin Learned from Thomas Darwin Learned from Thomas MalthusMalthus

• Thomas Malthus was an economist.• Malthus reasoned that humans have

the potential to reproduce beyond the capacity of their food supply.

• Malthus recognized that there are some limitations to human population growth:– War (for animals it is predation-predators)– Disease– Starvation

CompetitionCompetition

• Because there are some limitations to growth, Darwin thought that those survivors must be better equipped (adapted) to their environment allowing them to out-compete other individuals.

• The offspring of the successful competitors have the same traits so are also more likely to survive in the same kind of environment.

Natural SelectionNatural SelectionDarwin theorized that evolution occurs through

a process he called natural selection1. Overproduction – Each species produces

more offspring that will naturally survive.2. Genetic Variation – individuals will be

slightly different from one another.3. Survival Struggle – competition for

resourcesAbiotic and Biotic factors

4. Successful Reproduction – fitness(Survival of the fittest)

More Evidence of EvolutionMore Evidence of Evolution• Darwin did not know what the

mechanism was for how parents passed their traits to their offspring.

• Gregory Mendel (1822-1884) the Catholic monk studied traits in sweet peas.

• With Mendel's work and biochemistry we now know that the mechanism is meiosis involving DNA that is subject to mutation.

MutationMutation• Changes to the heredity material- DNA,

deoxyribonucleic acid – result in a changed genotype.

• Some changes that occur are not observed because the change did not significantly affect a function. Changes that affect function result in a different phenotype (what things look or function like).

Types of MutationTypes of Mutation• Changes can occur by • single nucleotide substitutions• Insertions or deletions of longer

sequences of nucleotides (the components that make up deoxyribonucleic acid

• Chromosome alterations – which can be seen with a microscope.

Some Phrases about Some Phrases about EvolutionEvolution

Asking and Answering Asking and Answering “How?” and “Why?”“How?” and “Why?”

• How and why questions are usually answered using a hypothetical-deductive (H-D) approach. – hypothesize– predict– test! - experiments (field + lab)

Hypothesis vs. Theory

“Evolution is just a theory”Scientific theories are factual

statements about Nature.

Good theories are logically supported

and are demonstrated by the results from multiple tests.

“Evolution is about the Origins of Life”

The Theory of Evolution mostly describes how change occurred

after complex life arose.

"Nature red in tooth and claw"

Evolution says nothing about which traits will evolve;

only that they will change.

"Survival of the Fittest" Cultural and ethical decisions of who is

“fittest” and should survive are not Nature’s Laws. The term is used in

business but with a different definition of fittest

This is different from…..when fitness involves reproduction and those organisms that reproduce have

demonstrated fitness.