ch. 5 evolution apes mrs. sealy. i. origins of life how do we know? chemical analysis: chemists have...
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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
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
• 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
• 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
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:
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
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