Ch. 5 Evolution

APES

I. Origins of Life

• How do we know?• Chemical analysis: chemists have

conducted lab experiments to show how simple organic compounds could have been created.

• Radioactive dating: radiocarbon, radiometric dating with radioactive rocks and fossils

Electrical sparkssimulating lightingprovide energy tosynthesize organic compounds

Sample for chemical analysis

Cooled water containing organic compounds

Cold water

Condenser

Electrode

Water vapor

H2O

CH4

CO2N2

NH3 H2

H2O

Fig. 5.3, p. 104

Life evolved in two phases over the course of 4.7-4.8 billion years• Chemical evolution of organic

molecules and polymers• Biological evolution from single celled

prokaryotic bacteria to multi-cellular eukaryotic organisms

Chemical Evolution

• Formation of the Earth’s Crust: 4.6 to 4.7 billion years ago a cloud of cosmic dust condensed into planet earth which soon turned molten due to radioactive decay and meteorite impacts. As cooling took place a thin crust developed.

• Formation of the earth’s seas: volcanic eruptions and comet impacts brought water vapor that rained down on earth to create the sea

Chemical Evolution (cont.)

• Small organic molecules form in the seas: from eroded minerals from rocks

• 4.4 billion years ago the first atmosphere was formed. The main components were believed to be: CO2, N2,H2O , CH4, NH3, H2S, HCL, no oxygen

• This mixture is often to as: The primordial stew or soup theory.

Chemical Evolution (cont.)• Large organic molecules form in the seas:

energy from lightening, heat from volcanoes, and UV light and the chemicals in the atmosphere combined to form the first large organic molecules such as amino acids and carbs.

• Another theory is that these large molecules formed in hydrothermal vents.

• First protocells form in the seas: these new compounds washed into the seas and sat for millions of years to form the first DNA and protocells

Formationof the

earth’searly

crust andatmosphere

Small organic

moleculesform in

the seas

Large organic

molecules(biopolymers)

form inthe seas

First protocells

form inthe seas

Single-cellprokaryotes

form inthe seas

Single-celleukaryotes

form inthe seas

Variety ofmulticellularorganismsform, first

in the seas and lateron land

Chemical Evolution(1 billion years)

Biological Evolution(3.7 billion years)

Fig. 5.2, p. 103

Biological Evolution

• 3.5 to 3.8 billion years ago, well below the surface of the sea away from harmful UV radiation the first prokaryotic cells formed: PROKARYOTIC

• 2.3 to 2.5 billion years ago the first cyanobacteria appear and they: photosynthesize

• 2.0-2.1 billion years ago oxygen: formed from cyanobacteria

• 1.2 billion years ago we see the first eukaryotic cells arrive, which could reproduce sexually and produce a wide variety of organisms

• 400-500 million years ago we see: the first land plants and animals

• How do we know what organisms were around:– Fossil record– Radiometric dating of rocks near the fossils

Fig. 5.4, p. 105

Fossils present but rare

Evolution and expansion of life

Fossils become abundant

Plants invade the land

Age of reptiles

Age of mammals

Insects and amphibians invade the land

Modern humans (Homo sapiens) appear about 2 seconds before midnight

Recorded human history begins 1/4 second before midnight

Origin of life (3.6–3.8 billion years ago)

Evolution

• Heritable changes in a population’s genetic make-up through successive generations

• An overwhelming majority of biologists believe that this is the best explanation for the changes that have occurred over the last 3.7 billion years and also for why life on earth today is so diverse.

• The theory of evolution is based on the idea that all species descended from other specieshttp://

www.hippocampus.org/Biology

1st generation 2nd Generation

GG, Gg = green beetle

gg = brown beetle

Evolution= shift in gene frequency in a population

Macroevolution

• long term, large scale evolutionary changes among a group or species. One species leads to the appearance of many other species.

Genetic persistence:

• The inheritance of DNA molecules from the origin of the first cells through all subsequent lines of descent which is the basis of the unity of life

Genetic divergence

• Long term changes in lineage’s of species, which are the basis of the diversity of life

Genetic losses

• The steady background extinction or relatively abrupt catastrophic loss of lineage

• Microevolution: the small genetic changes that a population experiences

• How does microevolution work?

• It is the development of genetic variability in a population

• A population’s gene pool is the sum total of all genes possessed by the individuals of the population’s species

• Microevolution is a change in the species gene pool over time

• Members of a population have different molecular forms of the same gene called alleles. Sexual reproduction leads to a shuffling of alleles. As a result each individual has a different combination of alleles. This is called genetic variability

• Microevolution works through a combination of four processes: every

• Mutation, natural selection, gene flow, genetic drift

Mutation:

• The source for all new alleles (genes) is mutations, which are random changes in the structure of DNA molecules in a cell.

• Adaptation: any genetically controlled trait that helps an organism survive and reproduce under a given set of environmental conditions

• Every so often a mutation is beneficial and the result is a new genetic trait that will ensure the survival of offspring better

• Mutations are rare

Natural Selection

• Differential reproduction: because of random shuffling or recombination of genes, certain individuals may by chance have one or more beneficial adaptations that allow them to survive under various environmental conditions. As a result they are more likely to reproduce than individuals that do not have such adaptations.

• Natural selection does not create favorable genes; instead it favors some individuals over others by acting on genes already in the gene pool.

• Natural selection occurs when the combined effects of adaptation and differential reproduction result in a particular beneficial gene becoming more common in succeeding generations

Three types of Natural Selection:• Directional: it pays to be

different: changing environmental conditions cause gene frequencies to shift so that individuals with traits at one end of the normal range become more common than midrange species

Directional Natural Selection

Natural selection

New average Previous average

Num

ber

of in

divi

dual

s

Coloration of snails

Proportion of light-coloredsnails in population increases

Num

ber

of in

divi

dual

s

Snail colorationbest adaptedto conditions

Average

Coloration of snails

Fig. 5.6a, p. 110

Average shifts

• Stabilizing: it pays to be average: in a stable environment species that have abnormal genes have no advantage and tend to be eliminated.

Stabilizing Natural Selection

Coloration of snails

Light snailseliminated

Dark snailseliminated

Num

ber

of in

divi

dual

s

Coloration of snails

Snails withextreme

coloration areeliminated

Num

ber

of in

divi

dual

s

Average remains the same,but the number of individuals withintermediate coloration increases

Fig. 5.6b, p. 110

Natural selection

• Diversifying: it doesn’t pay to be normal: when environmental conditions favor individuals at both extremes of the genetic spectrum and sharply reduce the number of mid-range individuals.

Number of individuals with light and dark coloration

increases, and the number with intermediate coloration decreases

Coloration of snails

Num

ber

of in

divi

dual

s Snails with light and darkcolors dominate

Diversifying Natural Selection

Coloration of snails

Num

ber

of in

divi

dual

s

Light colorationis favored

Darkcolorationis favored

Intermediate-colored snails are selected against

Fig. 5.6c, p. 110

Natural selection

Gene Flow:

Movement of genes between populations

Genetic drift:

• involves change in a genetic composition of a population by chance and is important in small populations

Co evolution

• When populations of two different species interact over a long time, changes in the gene pool of one species can lead to changes in the gene pool of the other species. For example:

An Example of evolution by natural selection:

The peppered moths of EnglandDuring the industrial revolution.http://www.echalk.co.uk/Science/

Biology/PepperedMoth/Peppered_MothWEB.swf

Coevolution

Coevolution can occur between animals that have a symbiotic relationship as well those who have a predator prey relationship

Coevolution gone awry

Ecological Niches and AdaptationEcological niche: the species way of life

or the functional role of the species in an ecosystem. For example:

• a. types of resources used• b. range of tolerance• c. how it interacts with components of

the ecosystem• d. its role in flow of energy and matter

cycling

Fundamental vs realized niche

• Fundamental niche vs. realize niche: Your fundamental niche is all the possible conditions that you can live under. Your realized niche is how you are actually living. For example: you may be capable being a star, but competition keeps you from getting the job

Region of niche overlap

Generalist specieswith a broad nicheGeneralist species

with a narrow nicheNiche

breadth

Nicheseparation

Num

ber

of in

divi

dual

s

Resource use

Fig. 5.7, p. 111

Generalist species vs. Specialist speciesGeneralist: have very broad niches and

eat a variety of foods and can live in a variety of places under differing conditions. For example cockroach

Specialist: narrow niche, may only be able to live in one type of habitat or eat only one type of food. For example: panda bear

– Is it better to be a generalist or a specialist?

Speciation • Two species arise from one species in

response to changes in environmental conditions.

• The mechanism for speciation occurs in two phases– Geographic isolation: occurs when two

populations of a species becomes physically separated for long periods

– Reproductive isolation: occurs as mutation and natural selection occur independently in two separated populations of the same species. Eventually, the changes are so great that two groups will no longer interbreed.

Adapted to heatthrough lightweightfur and long ears, legs, and nose, whichgive off more heat.

Adapted to coldthrough heavierfur, short ears,short legs, shortnose. White furmatches snowfor camouflage.

Gray Fox

Arctic Fox

Different environmentalconditions lead to differentselective pressures and evolutioninto two different species.

Spreadsnorthwardandsouthwardandseparates

Southernpopulation

Northernpopulation

Early foxpopulation

Fig. 5.8, p. 113

Convergent evolution:

• Two separate species will evolve separately to create animals with similar characteristics. Species that have similar niches tend to evolve similar sets of traits in response similar environmental conditions. For example:

Divergent evolution: speciation creates separate species

Extinction• When environmental changes occur species either

evolve or cease to exist and their genetic material is permanently lost.

• Extinction patterns have been caused by large-scale movements of the continents and gradual climate changes like those from meteors and volcanoes.

• All species inevitably disappear• Background extinction is the low rate that species

constantly disappear. It is the normal level. Approx.

3 species per year• Mass extinction: an abrupt rise in extinction rates

above the background rate. It is catastrophic, global and often results in 25% to 70% loss of species

• There are have been five previous mass extinctions and we are currently in the six mass extinction, which is being caused by humans.

– Speciation minus extinction equals biodiversity

– Although extinction is a natural process, humans have sped up the process and we have lost a lot of genetic material

– This mass extinction is different from previous extinctions in the following ways:

– 1. First time it has ever been caused by one species

– 2. This is the fastest it has every happened– 3. Adaptive Radiation will be slow after

because we are destroying habitats

Ordovician: 50% of animal families, including many trilobites

Devonian: 30% of animal families, including agnathan and placoderm fishes and many trilobites.

Permian: 90% of animal families, including over 95% of marine species; many trees, amphibians, most bryozoans and brachiopods, all trilobites.

Triassic: 35% of animal families, including many reptiles and marine mollusks.

Cretaceous: up to 80% of ruling reptiles (dinosaurs); many marine species including manyforaminiferans and mollusks.

Current extinction crisis causedby human activities. Many speciesare expected to become extinctwithin the next 50–100 years.

Species and families experiencing mass extinction

Bar width represents relative number of living species

Extinction

Millions ofyears ago

PeriodEraP

aleo

zoic

Mes

ozo

icC

eno

zoic Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

Today

65

180

250

345

500Extinction

Extinction

Extinction

Extinction

Extinction

Fig. 5.10, p. 115

Adaptive Radiation

• Adaptive radiation: an extinction of one species is an opportunity for another species and after a mass extinction there is a period in which numerous new species can evolve

• Speciation and extinction affects biodiversity:

Monotremes(platypus, etc.)

Elephants

Odd-toed hoofed mammals

Even-toed hoofed mammals

Whales

Carnivores

Insectivores

Bats

Primates

Rodents

Rabbits

Marsupials(kangaroos, etc.)

CenozoicMesozoic

Fig. 5.11, p. 116

How does Macroevolution occur?A. Macroevolution is concerned with how evolution

takes place above the level of species and over long periods of time and shows how small changes can lead to the eventual creation of many different species, genera and families.

B. Gradualist model: theory that says macro evolutionary change occurs over many millions of years

C. Punctuated Equilibrium: opposing theory that says there are long periods of relatively punctuated with brief periods of very rapid changes.

• D. In reality it is probably a combination of both

Common Misconceptions about Evolution• “Survival of the fittest” is often

misinterpreted as “survival of the strongest”. In biological terms fitness is a measure of reproductive success and the ones with the most descendants are the fittest. Natural selection is not "tooth and claw” competition.

• “Humans evolved from apes”, this is not true. Apes and humans have a common ancestor from which both are descended.

• Nature has a grand plan in which species become progressively more perfect, natural selection is random and there is no goal of perfection.

• 1) Before 5 mya: In Africa, our ancestral lineage and the chimpanzee lineage split.

• 2) Before 4 mya: The hominid Australopithecus anamensis walked around what is now Kenya on its hind legs.

• 3) >3 mya: Australopithecus afarensis (“Lucy”) lived in Africa.• 4) 2.5 mya: Some hominids made tools by chipping stones to

form a cutting edge. There were perhaps four or more species of hominid living in Africa.

• 5) 2 mya: The first members of the Homo clade, with their relatively large brains, lived in Africa

• 6) 1.5 mya: Hand axes were used. Also, hominids had spread out of Africa and into much of Asia and Europe. These hominids included the ancestors of Neanderthals (Homo neanderthalensis) in Europe and Homo erectus in Asia.

• 7) 100,000 years ago: Human brains reached more or less the current range of sizes. Early Homo sapiens lived in Africa. At the same time, Homo neanderthalensis and Homo erectus lived in other parts of the Old World.

• 8) 50,000 years ago: Human cultures produced cave paintings and body adornment, and constructed elaborate burials. Also, some groups of modern humans extended their range beyond Africa.

• 9) 25,000 years ago: Other Homo species had gone extinct, leaving only modern humans, Homo sapiens, spread throughout the Old