Post on 03-Dec-2014
description
Prepared by: Ms. IRISH M. SEQUIHOD
Essential Questions• Be able to describe how the earth is “just
right” for life• What are the evidences of evolution?• What is evolution? How has evolution lead
to the current diversity of organisms?• What is an ecological niche? How does it
relate to adaptation to changing environmental conditions?
• How do extinction of species and formation of new species affect biodiversity?
A Theory or a Fact?
Evolution as Theory and Fact
• Confusion sometimes arises as to • whether Evolution is a theory or a fact.• Actually it is both!
• The theory of Evolution deals with how• Evolution happens. Our understanding• of this process is always changing.
• Evolution is also a fact as there is a• huge amount of indisputable evidence • for its occurrence.
The Earth: The PERFECT PLANET• Temperature
– Distance from Sun– Geothermal energy from core– Temperature fluctuated only 10-20oC over 3.7
billion years despite 30-40% increase in solar output
• Water exists in 3 phases• Right size (=gravitational mass to keep atmosphere)• Resilient and adaptive• Each species here today represents a long chain of
evolution and each plays a role in its respective ecosystem
Summary of Evolution of Life
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)
Biological Evolution
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 midnightRecorded human history begins 1/4 second before midnight
Origin of life (3.6–3.8 billion years ago)
Evidence (1): Biochemistry
• The basic similarity of all living things suggests• that they evolved from a single common ancestor.
• As we have already seen, all living things pass• on information from generation to generation• using the DNA molecule.
• All living things also use a molecule• called ATP to carry• energy around the• organism.
DNA for
Information Transfer
ATP for Energy Transfer
Evidence (2): Similar GenesHUMAN CCAAGGTCACGACTACTCCAATTGTCACAACTGTTCCAACCGTCACGACTGTTGAACGACHIMPANZEE CCAAGGTCACGACTACTCCAATTGTCACAACTGTTCCAACCGTCATGACTGTTGAACGAGORILLA CCAAGGTCACAACTACTCCAATTGTCACAACTGTTCCAACCGTCACGACTGTTGAACGA
• If evolution is true then we might also expect that closely related organisms will be more similar to one another than more distantly related organisms.
• Comparison of the human genetic code with that of other organisms show that chimpanzees are nearly genetically identical (differ by less than 1.2%) whereas the mouse differs by ≈15%.
Genetic code of chimps and gorillas is almost identical to humans
Evidence (3): Comparative Anatomy
• Similar comparisons can be made based on anatomical evidence.
• The skeleton of humans and gorillas are very similar suggesting they shared a recent common ancestor, but very different from the more distantly related woodlouse…
yet all have a common shared characteristic: bilateral symmetry
Human and GorillaWoodlouse
Evidence (4): Homology
The pentadactyl limb is ancestral to all vertebrates…
but modified for different uses
Evidence (5): Vestigial Structures
The coccyx is a vestigial tail
• As evolution progresses, some structures get side-lined as they are not longer of use. These are known as vestigial structures.
• The coccyx is a much reduced version of an ancestral tail, which was formerly adapted to aid balance and climbing.
• Another vestigial structure in humans is the appendix.
Evidence (6): Fossil Record
The fossil record shows a sequence from simple bacteria to more complicated organisms through time and provides the most compelling evidence for evolution.
Fossil formationThere are many ways in which an organism can be fossilised
One of these ways is shown in the next sequence of slides
In principle, a fossil is formed when an organism dies, its body is enclosed in mud, or sand. The soft parts decay but some of the hard parts (skeleton, shells, seeds) are preserved
The mud or sand eventually becomes rock and the hard parts of theorganism are mineralised.
When the rock is exposed as a result of earth movements or erosion,the fossil remains can be dug out and studied.
Living fish A
Dies
Enclosed in sediment
Hard parts fossilised
Living fish B
Dies
Enclosed in sediment
Hard parts fossilised
Fish B becomes a fossil much later than fish A
The sediment eventually becomes rock
The deeper the rock layer, the older the fossil
4
fish skeleton fossilisedolder sedimentbecomes rock
more recent sediment collects6
land raised abovewater level
recent rock
older rock
7
Earth’s crust movement
earth movements fracture rock
fossilised skeleton exposed
8
Evidence (7): Transitional fossils
Archaeopteryx
• Many fossils show a clear transition from one species, or group, to another.
• Archaeopteryx was found in Germany in 1861. It share many characteristics with both dinosaurs and birds.
• It provides good evidence that birds arose from dinosaur ancestors
Evidence (8): Geography
• Geographic spread of organisms also tells of their past evolution.
• Marsupials occur in two populations today in the Americas and Australia.
• This shows the group evolved before the continents drifted apart
Evidence (9): Antibiotic resistance
• We are all familiar with the way that certain bacteria can become resistant to antibiotics
• This is an example of natural selection in action. The antibiotic acts as an environmental pressure. It weeds out those bacteria with low resistance and only those with high resistance survive to reproduce.
Staphylococcus
Charles Darwin
• Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms.
• A scientific theory is a well-supported testable explanation of phenomena that have occurred in the natural world.
Voyage of the Beagle
Voyage of the Beagle
• Dates: February 12th, 1831• Captain: Charles Darwin• Ship: H.M.S. Beagle• Destination: Voyage around the world.• Findings: evidence to propose a revolutionary
hypothesis about how life changes over time
Voyage of the Beagle
Patterns of Diversity
• Darwin visited Argentina and Australia which had similar grassland ecosystems.
– those grasslands were inhabited by very different animals.
– neither Argentina nor Australia was home to the sorts of animals that lived in European grasslands.
Patterns of Diversity
• Darwin posed challenging questions. – Why were there no rabbits in Australia, despite
the presence of habitats that seemed perfect for them?
– Why were there no kangaroos in England?
Living Organisms and Fossils
• Darwin collected the preserved remains of ancient organisms, called fossils.
• Some of those fossils resembled organisms that were still alive today.
Others looked completely unlike any creature he had ever seen.
• As Darwin studied fossils, new questions arose. – Why had so many of these species disappeared? – How were they related to living species?
The Galapagos Island
• The smallest, lowest islands were hot, dry, and nearly barren-Hood Island-sparse vegetation
• The higher islands had greater rainfall and a different assortment of plants and animals-Isabela- Island had rich vegetation.
• Darwin was fascinated in particular by the land tortoises and marine iguanas in the Galápagos.
• Giant tortoises varied in predictable ways from one island to another.
• The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.
The Galapagos Island
Animals found in the Galapagos
• Land Tortoises
• Darwin Finches
• Blue-Footed Booby
• Marine Iguanas
The Journey Home
• Darwin Observed that characteristics of many plants and animals vary greatly among the islands
• Hypothesis: Separate species may have arose from an original ancestor
Ideas that shaped Darwin’s Thinking
• James Hutton: • 1795 Theory of
Geological change– Forces change
earth’s surface shape
– Changes are slow– Earth much older
than thousands of years
Ideas that shaped Darwin’s Thinking
• Charles Lyell• Book: Principles of
Geography• Geographical features
can be built up or torn down
• Darwin thought if earth changed over time, what about life?
Ideas that shaped Darwin’s ThinkingPopulation Growth
• Thomas Malthus-19th century English economist
• If population grew (more Babies born than die)– Insufficient living
space– Food runs out– Darwin applied this
theory to animals
Discovery (1) Fixed species
From Classical times until long after the Renaissance, species were considered to be special creations, fixed for all time.
Discovery (2): Transmutation
en.wikipedia.org/wiki/Image:Giraffe_standing.jpgcommons.wikimedia.org/wiki/Image:Jean-baptiste_lamarck2.jpg
Jean Baptiste de Lamarck
• Around 1800, scientists began to wonder whether species could change or transmute.
• Lamarck thought that if an animal acquired a characteristic during its lifetime, it could pass it onto its offspring. • Hence giraffes got their long necks through generations of straining to reach high branches.
Discovery (3): Fossils and Stratahttp://en.wikipedia.org/wiki/ImageWilliam_Smith.g.jpg
http://en.wikipedia.org/wiki/Image:Geological_map_of_Great_Britain.jpg
http://en.wikipedia.org/wiki/Image:Smith_fossils2.jpg
William Smith, his geology map & some of his fossil specimens
At about the same time, geologists like William Smith weremapping the rocks and fossils of Britain. He and others showed that different species existed in the past compared with today.
Discovery (4): Darwin’s Voyage
en.wikipedia.org/wiki/Image:Charles_Darwin_by_G._Richmond.jpgen.wikipedia.org/wiki/Image:HMS_Beagle_by_Conrad_Martens.jpg
Voyage of the Beagle
• From 1831-1836, a young naturalist called Charles Darwin toured the world in HMS Beagle.
• He was dazzled by the amazing diversity of life and started to wonder how it might have originated
Discovery (5): Survival of the Fittest
en.wikipedia.org/wiki/Image:Darwin%27s_finches.jpeg
• In his Origin of Species, published in 1859, Darwin proposed how one species might give rise to another.
• Where food was limited, competition meant that only the fittest would survive.
• This would lead to the natural selection of the best adapted individuals and eventually the evolution of a new species.
Darwin in 1860
Natural Selectionexplains adaption
Discovery (6): Huxley v. Wilberforce
www.bbc.co.uk/religion/galleries/spiritualhistory/images/9.jpg
• Darwin’s idea of Evolution by Natural Selection was met with huge controversy.
• A famous debate in 1860 pitted Bishop Wilberforce against Darwin’s bulldog, Thomas Henry Huxley.Bishop Wilberforce v. T. H. Huxley
• Evolutionists got the better of the debate, but few were convinced by Darwin’s idea of Natural Selection.
Discovery (7): Genetics
en.wikipedia.org/wiki/Image:Mendel.pngen.wikipedia.org/wiki/Image:Doperwt_rijserwt_peulen_Pisum_sativum.jpg
Mendel and his peas • From 1856-63, a monk called Gregor Mendel cultivated 29,000 pea plants to investigate how evolution worked i.e., how characteristics were passed down the generations.
• He figured out the basic principles of genetics. He showed that offspring received characteristics from both parents, but only the dominant characteristic trait was expressed. Mendel’s work only came to light in 1900, long after his death
Discovery (8): Making Sense• In the early 20th century, scientist started to make sense of how evolution worked.
• Building on Mendel’s genetics, studies showed how characteristics in a population could be selected by environmental pressures.
• This Modern Synthesis, as Julian Huxley called it, brought Darwin’s Natural Selection back to the centre of evolutionary theory.
en.wikipedia.org/wiki/Image:Hux-Oxon-72.jpg
Julian Huxley and the Modern Synthesis
Discovery (9): Opposition
www.templeton-cambridge.org/fellows/vedantam/publications/2006.02.05/eden_and_evolution/
• Despite the achieval of scientific consensus on evolution, some Christian groups continued to oppose the concept.
• In 1925, the teaching of evolution was outlawed in Tennessee, USA, resulting in the infamous Scopes Monkey Trial Outside the Scopes Trial
Discussion: Should Creationism and Evolution be given equal time in science lessons?
science.kukuchew.com/wp-content/uploads/2008/01/stop_following_me_creationist.jpg
Mechanism (1): All in the Genes
commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG
• The genetic make-up of an organism is known as its genotype.
• An organism’s genotype and the environment in which it lives determines its total characteristic traits i.e. its phenotype.
PhenotypeGenotype
Mechanism (2): DNA
Watson and Crick and their model of DNA
www.chem.ucsb.edu/~kalju/chem110L/public/tutorial/images/WatsonCrick.jpgen.wikipedia.org/wiki/DNA
DNA replication
• The double-helix structure of DNA was discovered in 1953.
• This showed how genetic information is transferred from one cell to another almost without error.
Mechanism (3): Mutation
upload.wikimedia.org/wikipedia/commons/7/79/Types-of-mutation.png humansystemstherapeutics.com/bb.htm
Types of mutation
Mutant fruitfly
• However, occasional mutations or copying errors can and do occur when DNA is replicated.
• Mutations may be caused by radiation, viruses, or carcinogens.
• Mutations are rare and often have damaging effects. Consequently organisms have special enzymes whose job it is to repair faulty DNA.
Mechanism (4): Variation
majorityrights.com/index.php/weblog/comments/racial_variation_in_some_parts_of_the_skull_involved_in_chewing/
• Nevertheless, some mutations will persist and increase genetic variation within a population.
• Variants of a particular gene are known as alleles. For example, the one of the genes for hair colour comprises brown/blonde alleles.
Mechanism (5): Natural Selection
en.wikipedia.org/wiki/Image:Mutation_and_selection_diagram.svg
• Mutant alleles spread through a population by sexual reproduction.
• If an allele exerts a harmful effect, it will reduce the ability of the individual to reproduce and the allele will probably be removed from the population.
• In contrast, mutants with favorable effects are preferentially passed on
Selection of dark gene
Mechanism (6): Peppered Moth
http://en.wikipedia.org/wiki/Image:Biston.betularia.7200.jpgen.wikipedia.org/wiki/Image:Biston.betularia.f.carbonaria.7209.jpgen.wikipedia.org/wiki/J._B._S._Haldane
• The Peppered Moth is an example of Natural Selection in action discovered by Haldane
• During the Industrial Revolution the trees on which the moth rested became soot-covered.
Haldane and the peppered moth
• This selected against the allele for pale colour in the population (which were poorly camouflaged from predators) and selected for the dark colour allele.
Mechanism (7): Microevolution
www.puppy-training-solutions.com/image-files/dog-breed-information.jpg
• The dog is another example of how selection can change the frequency of alleles in a population.
• Dogs have been artificially selected for certain characteristics for many years, and different breeds have different alleles. • All breeds of dog belong to the same species, Canis lupus (the wolf) so this is an example of Microevolution as no new species has resulted.
Dogs are wolves
Mechanism (8): Macroevolution
www.ingala.gov.ec/galapagosislands/images/stories/ingala_images/galapagos_take_a_tour/small_pics/galapagos_map_2.jpg
Galapagos finches
• However, if two populations of a species become isolated from one another for tens of thousands of years, genetic difference may become marked.
• If the two populations can no-longer interbreed, new species are born. This is called Macroevolution.
• Darwin’s Galapagos finches are an example of this process in action.
Mechanism (9): Speciation Today?
en.wikipedia.org/wiki/Image:Gb-lu-Angel-southbound.jpgen.wikipedia.org/wiki/Culex
London Underground Mosquito
• The mosquito was introduced to the London Underground during its construction around 1900.
• It became infamous in the War for attacking people sheltering from the Blitz.
• Studies indicate several genetic differences from its above-ground ancestors. Interbreeding between populations is difficult suggesting that speciation may be occurring.
4 major mechanisms that drive evolution:
• Natural Selection• Mutation• Gene Flow• Genetic Drift
Unifying Principles of Evolution
• Perpetual Change: All species are in a continuous state of change
Unifying Principles of Evolution
• *Nature- The combined influences of physical and biological limiting factors* acting upon an organism.
Unifying Principles of Evolution• *Limiting Factor- Any factor (physical or biological)
which regulates• the welfare of an organism
–Disease, competition, predation, environmental change, etc.
Darwinian Natural Selection
• Three conditions necessary for evolution by natural selection to occur:– Natural variability for a trait in a population– Trait must be heritable– Trait must lead to differential reproduction
• A heritable trait that enables organisms to survive AND reproduce is called an adaptation
Steps of Evolution by Natural Selection
• Genetic variation is added to genotype by mutation• Mutations lead to changes in the phenotype• Phenotype is acted upon by nat’l selection• Individuals more suited to environment produce more
offspring (contribute more to total gene pool of population)• Population’s gene pool changes over time• Speciation may occur if geographic and reproductive isolating
mechanisms exist…• Natural Selection in action ...• A demonstration...
Selection Against or in Favor of Extreme Phenotypes
• Stabilizing Selection– Intermediate forms of a trait
are favored
– Alleles that specify extreme forms are eliminated from a population
– EX: Birth Weight and Clutch Size
Stabilizing 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 sameNumber of individuals with
intermediate coloration increases
Eliminates Fringe Individuals
Natural selection
Selection Against or in Favor of Extreme Phenotypes
• Disruptive Selection– Both forms at extreme
ends are favored
– Intermediate forms are eliminated
– Bill size in African finches
Directional Change in the Range of Variation
• Directional Selection– Shift in allele frequency in a
consistent direction
• Phenotypic Variation in a population of butterflies
MUTATIONS, MY FRIENDS!
• Changes in the structure of the DNA
• Adds genetic diversity to the population
• May or may not be adaptive– Depends on the environment!
Sooooo….What’s Evolution?• The change in a POPULATION’S genetic makeup (gene pool) over
time (successive generations)– Those with selective advantages (i.e., adaptations), survive and reproduce– All species descended from earlier ancestor species
• Microevolution• Small genetic changes in a population such as the
spread of a mutation or the change in the frequency of a single allele due to selection (changes to gene pool)– Not possible without genetic variability in a pop…
• Macroevolution– Long term, large scale evolutionary changes through which new
species are formed and others are lost through extinction
Microevolution• Changes in a population’s gene pool over time.
– Genetic variability within a population is the catalyst• Four Processes cause Microevolution
– Mutation (random changes in DNA—ultimate source of new alleles) [stop little]
• Exposure to mutagens or random mistakes in copying• Random/unpredictable relatively rare
– Natural Selection (more fit = more offspring)– Gene flow (movement of genes between pop’s)– Genetic drift (change in gene pool due to
random/chance events)
The Case of the Peppered Moths
• Industrial revolution– Pollution darkened tree trunks
• Camouflage of moths increases survival from predators
• Directional selection caused a shift away from light-gray towards dark-gray moths
Fig. 18.5, p. 287
Gene Flow and Genetic Drift
• Gene Flow– Flow of alleles
• Emigration and immigration of individuals
• Genetic Drift– Random change in allele frequencies over generations brought
about by chance
– In the absence of other forces, drift leads to loss of genetic diversity
• Elephant seals, cheetahs
Speciation
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
Speciation• Two species arise from one
– Requires Reproductive isolation• Geographic: Physically separated• Temporal: Mate at different times• Behavioral: Bird calls / mating rituals• Anatomical: Picture a mouse and an elephant hooking up• Genetic Inviability: Mules
• Allopatric– Speciation that occurs when 2 or more populations of a species are
geographically isolated from one another – The allele frequencies in these populations change– Members become so different that that can no no longer interbreed– See animation
• Sympatric– Populations evolve with overlapping ranges– Behavioral barrier or hybridization or polyploidy
COEVOLUTION: Interaction Biodiversity
• Species so tightly connected, that the evolutionary history of one affects the other and vice versa.– Ant Farmers of the Amazon
Coevolution
• Interactions between species can cause microevolution– Changes in the gene pool of one species can cause changes in
the gene pool of the other• Adaptation follows adaptation in something of a long
term “arms race” between interacting populations of different populations– The Red Queen Effect
• Can also be symbiotic coevolution– Angiosperms and insects (pollinators)– Corals and zooxanthellae – Rhizobium bacteria and legume root nodules
And NUH is the letter I use to spell Nutches,Who live in small caves, known as Niches, for hutches.These Nutches have troubles, the biggest of which isThe fact there are many more Nutches than Niches.Each Nutch in a Nich knows that some other NutchWould like to move into his Nich very much.So each Nutch in a Nich has to watch that small NichOr Nutches who haven't got Niches will snitch.
-On Beyond Zebra (1955)
Dr. Seuss
Niches• A species functional role in an ecosystem• Involves everything that affects its survival and reproduction
– Includes range of tolerance of all abiotic factors– Trophic characteristics– How it interacts with biotic and abiotic factors– Role it plays in energy flow and matter cycling
• Fundamental Niche– Full potential range of physical chemical and biological conditions and
resources it could theoretically use if there was no direct competition from other species
• Realized Niche– Part of its niche actually occupied
• Generalist vs. Specialist– Lives many different places, eat many foods, tolerate a wide range of
conditions vs few, few, intolerant…– Which strategy is better in a stable environment vs unstable?
Competition and Community Diversity
•Species evolve to minimize competition and niche overlap
•Results in a diverse matrix of differing species within a community
Local, ecological and true extinctionThe ultimate fate of all species just as death is for all individual organisms99.9% of all the species that have ever existed are now extinct
To a very close approximation, all species are extinctBackground vs. Mass Extinction
Low rate vs. 25-90% of totalFive great mass extinctions in which numerous new species (including mammals) evolved to fill new or vacated niches in changed environments10 million years or more for adaptive radiations to rebuild biological diversity following a mass extinction
Extinctions open up new opportunities for speciation and adaptive radiation..BUT you can have too much of a good thing!
Factors Affecting Extinction Rates• Natural Extinctions
– Climate change– Cataclysmic event (volcano, earthquake)
• Human Activities– Habitat Loss/Fragmentation– Introduction of exotic/invasive species– Pollution– Commercial harvesting– Accidental killing (tuna nets)– Harassing– Pet Trade– Urbanization– Damming/Flooding– Agricultural conversion
Extinction in the Context of Evolution
• If – the environment changes rapidly and– The species living in these environments do not
already possess genes which enable survival in the face of such change and
– Random mutations do not accumulate quickly enough then,
• All members of the unlucky species may die
Biodiversity• Speciation – Extinction=Biodiversity• Humans major force in the premature extinction of species.
Extinction rate increased by 100-1000 times the natural background rate.
• As we grow in population over next 50 years, we are expected to take over more of the earth’s surface and productivity. This may cause the premature extinction of up to a QUARTER of the earth’s current species and constitute a SIXTH mass extinction – Genetic engineering won’t solve this problem– Only takes existing genes and moves them around
• Know why this is so important and what we are losing as it disappears….
USING EVOLUTION AND GENETICS TO INFORM CONSERVATION
• EcoRegions Approach – Identifying biodiversity “hotspots” and focusing conservation efforts
on maintaining those ecosystems– Ex. Tropics, Appalachian Mountains, etc.
• “Umbrella Species” Conservation– Conserve one “sexy”, species and you conserve several others because
if the interactions they have with one another– Keystone species concept
• Species Survival Plan (SSP)– Zoo captive breeding programs– Population genetics in wild populations
• Ex. Cheetahs, Primates, Bears, etc.