DESCENT WITH MODIFICATION: A DARWINIAN VIEW OF LIFE
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DESCENT WITH MODIFICATION: A DARWINIAN VIEW OF LIFE
CHAPTER 22
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Fossils of trilobites, animals that lived in the seas hundreds of millions of years ago
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HISTORICAL CONTEXT
Carl Linnaeus (1707-1778) – founder of taxonomy (scientific name) grouped similar species into same genus
Georges Cuvier (1769-1832) – catastrophism – different species in layered rock due to catastrophic events like floods
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James Hutton (1726-1797) – gradualism – profound change is a cumulative product of slow but continuous process; ex. Rivers making canyons
Charles Lyell (1797-1875) – uniformitarianism – geological process have not changed throughout Earth’s history
Jean Baptiste Lamarck (1744-1829)- thought acquired characteristics can be passes on to offspring
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Formation of sedimentary rock and deposition of fossils from different time periods
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Strata of sedimentary rock at the Grand Canyon
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Charles Darwin in 1859, the year The Origin of Species was published
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CHARLES DARWIN (1809-1882)
Worked on the HMS Beagle in 1830’s
Observed and collected thousands of different species
Galapagos Islands (west of S. America) most interesting
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The Voyage of HMS Beagle
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Galápagos finches
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“The Galápagos tortoise (or Galápagos giant tortoise), is the largest living tortoise, endemic to nine islands of the Galápagos archipelago. Adults of large subspecies can weigh over 300 kilograms (660lb) and measure 1.2 meters (4 ft) long. Although the maximum life expectancy of a wild tortoise is unknown, the average life expectancy is estimated to be 150-200 years.”Source: en.wikipedia.org/wiki/Gal%C3%A1pagos_tortoise
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Darwin read Lyell’s Principles of Geology and felt age of earth was much older than previously thought
1844 Darwin wrote essay on the origin of species
1858 – Alfred Wallace sends manuscript to Darwin about Natural Selection
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Lyell presented Wallace’s paper as well as Darwin’s 1844 essay to scientists
1859 The Origin of Species published by DarwinDescent with modificationNatural selection (the
mechanism)
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Descent with modification
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DARWIN’S OBSERVATIONS
Individuals vary within a population Traits inherited All species are capable of
overproduction Many offspring do not survive
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DARWIN’S INFERENCES
Individuals with inherited traits that give them a better chance of surviving and reproducing tend to leave more offspring than those without those traits
Unequal ability of individuals to survive will lead to favorable traits in populations over generations.
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NATURAL SELECTION
A population evolves, not an individual!
Acquired characteristics may be adaptable but are not inherited!**
The environment does not create a best fit characteristic, but selects for it!
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A few of the color variations in a population of Asian lady beetles
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Artificial selection: diverse vegetables derived from wild mustard
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AP:April. 29, 2005 ST. THOMAS, Barbados - It's male. But what is it? A zonkey? A deebra? That's the debate in Barbados since a zebra gave birth to a foal sired by a donkey.
Goldendoodle and a liger
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EVIDENCE OF EVOLUTION Biogeography – geographical
distribution of speciesEx. Islands with similar species to
mainland Fossil record – transitional forms Comparative Anatomy –
homologous structures among different organisms
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Vestigial organs –marginal, if any importance, remnants of structures that once served a function Whale pelvis and leg bones and human appendix
Comparative Embryology – most vertebrates share common early development (gill slits)
Molecular Biology – similar overall DNA, similar proteins (ex. Cytochrome c)
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Evolution of insecticide resistance in insect populations
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Evolution of drug resistance in HIV
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Homologous structures: anatomical signs of descent with modification
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Molecular Data and the Evolutionary Relationships of Vertebrates
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Different geographic regions, different mammalian “brands”
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The evolution of fruit fly (Drosophila) species on the Hawaiian archipelago
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A transitional fossil linking past and present
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Left: Trilobite evolution Right: Whale evolution
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THE EVOLUTION OF POPULATIONS
Chapter 23
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GENETIC VARIATION
Genetic variation that makes evolution possibleMutations
Change in DNA sequences Average 1 in 100,000 genes per generation
Sexual reproduction Crossing over Independent assortment Fertilization
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POPULATION GENETICS Population – localized group of
individuals belonging to the same species Species – organisms that can interbreed
and produce fertile offspring Gene pool – total genes in a population If all members of a population are
homozygous for the same allele, that allele is fixed.
Gene frequency - two or more alleles for a gene, each having a relative frequency (proportion) in the gene pool
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Example:A = pinka = white 1000 plants = 200 white + 800 pink800 pink = 340(AA) + 460(Aa)
Find A’s frequency From AA: 340 x 2 = 680From Aa: 460 x 1 = 460680 + 460 = 11401140/2000 = .57 = .6The 2000 is total number of alleles for 1000
plants
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Find a’s frequency From aa: 200 x 2 = 400From Aa: 460 x 1 = 460400 + 460 = 860860/2000 = .43 = .4
Find A’s frequency1- .4 = .6
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HARDY-WEINBERG THEOREM
Frequencies of alleles and genotypes in a population’s gene pool remain constant over the generations unless acted upon by agents other than random sexual recombination
Hardy-Weinberg tells us what to expect if a population is NOT evolving!!
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The Hardy-Weinberg Theorem
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Random Gamete production
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The Hardy-Weinberg theorem
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EXAMPLE USING FLOWER POPULATION
Probability of picking 2 A from example.6 x .6 = .36
Probability of picking 2 a from example.4 x .4 = .16
Probability of picking Aa from example (aA or Aa)(.4 x .6) + (.6 x .4 ) = .48
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HARDY-WEINBERG EQULIBRIUM
The sexual process of meiosis and random fertilization maintain the same allele and genotype frequencies over generations.
In the example:p = .6 = Aq = .4 = a
p + q = 1p = 1 - q and q = 1 - p
p2 + 2pq + q2 = 1(AA)+ (2Aa) + (aa) = 1
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FIVE CONDITIONS FOR H-W
1. Very large population size2. No gene flow (genes entering or
leaving a population)3. No net mutations4. Random mating5. No natural selection
These mean NO EVOLUTION!
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MICROEVOLUTION
Microevolution – generational change in a population’s frequencies of alleles or genotypes
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FIVE AGENTS OF MICROEVOLUTION
1. Genetic Drift – rapid changes in a gene pool of a small, isolated population due to chance
Flip coin 10 times: may get 7 heads and 3 tails
Flip coin 1000 times: unlikely to get 700 head and 300 tails
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Genetic drift
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Two conditions that lead to genetic drift
a. Bottleneck Effect – genetic makeup of a small surviving population is unlikely to be representative of original population Northern elephant seals nearly
extinct due to hunting in late 1890’s which caused little genetic variation at 24 different loci
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The bottleneck effect: an analogy
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Cheetahs, the bottleneck effect (only 3 small populations in the wild)
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b.The Founder Effect – occurs when a few individuals colonize a new habitat; the smaller the sample size, the less the genetic makeup of the colonists will represent the gene pool of the large population they left
2. Gene Flow – a population may gain or lose alleles through genetic exchange due to immigration and/or emigration
Example: wind blowing pollen
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Bent grass grows on abandoned mine and is more copper tolerant that grass not near mine. Ongoing gene flow
makes hard for either population to fully adapt.
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Gene flow and human evolution
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3. Mutations- change in an organism’s DNA For any one gene locus,
mutation does not have much effect on population unless mutation is a benefit and allows for more offspring
Example: bacteria resistant to antibiotics
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Mutations – can only be passed on to offspring when they occur in cells that produce gametesOn rare occasions, a mutant allele
may be beneficial Ex. Houseflies resistant to DDT A single bacterium can make a billion cells in 10 hours so mutations can change whole populations quickly.
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4. Nonrandom mating – individuals choosing mates
Inbreeding – mating between closely related partners (extreme example is self-fertilization) Increases homozygous offspring, decreases heterozygous offspring
Assortive mating – individuals select partners like themselves
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5. Natural Selection – populations consist of varied individuals and some of these variants leave more offspring then others
White flowers easily seen by herbivorous insects so more pink survive to make more pink plants
Of all the agents of microevolution that change gene pools, only natural selection is likely to adapt a population to its environment.
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Figure 23.7 A nonheritable differences within a population (Map butterflies that emerge in spring are orange and brown and those that emerge in late
summer are black and white.)
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Geographic variation between isolated populations of house mice (on Madeira island which was settled by Portuguese who
brought mice with them in 15th century)
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Neutral Variation – variation that appears to have no selective advantage Example: fingerprints
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NATURAL SELECTION: Natural selection is the mechanism for
adaptive evolution. Darwinian fitness – the relative contribution
that an individual makes to the gene pool of the next generation
Relative fitness – the contribution of a genotype to the next generation compared to other alternative genotypes for same locus The highest relative fitness a genotype can
have is 1 If plants with white flowers average 80% as
many offspring as pink flowered plants, their relative fitness is 0.8
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NATURAL SELECTION EFFECTS
Stabilizing selection– acts against both of the extreme phenotypes and favors intermediatesExamples:
human birth weight in 3-4Kg range
horseshoe crab
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Directional selection– shifts towards one extreme phenotype (often during periods of environmental change)Examples:
bacteria resistant to antibiotics light vs. dark moths in England
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Directional selection for beak size in a Galápagos population of the medium ground finch
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Diversifying (disruptive) selection – when environmental conditions favors both extremes of a phenotypic rangeExamples:
finch population with 2 bill sizes butterfly with 2 distinct morphs
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Diversifying selection in a finch population
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Modes of selection
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Sexual dimorphism – distinction between the secondary characteristics of male and females
Sexual selection – selection process leading to sexual dimorphism
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Sexual selection and the evolution of male appearance
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Male peacock
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DIPLOIDY
Recessive alleles persist in environment due to heterozygotes
The rarer a recessive allele, the greater degree of protection a hybrid offers (especially if recessive allele is harmful)
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Heterozygote advantage – when a heterozygote has greater survivorship and reproductive success than any homozygoteExample: those who are carriers for
sickle cell anemia are resistant to malaria
Inbreeding can cause excessive homozygous conditions
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Normal and sickle cells
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Mapping malaria and the sickle-cell allele
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Frequency-dependent selection – the reproductive success of any one morph declines if that phenotypic form becomes too commonFemale African swallowtail
butterflies mimic several noxious species This would be less effective if only one species was imitated.
Right and left mouthed fish (cichlids) have different shaped mouths for approaching prey and eating scales
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THE ORIGIN OF SPECIES
Chapter 24
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Origin of Species
Macroevolution – the origin of new taxonomic groups
Speciation – the origin of new species
How does one species split into two?????
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A Galápagos Islands tortoise
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SPECIES Species - population(s) whose
members interbreed in nature and produce fertile offspring
The biological species concept is based on interfertility rather than physical similarity
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Diversity within species
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Reproductive isolation – barriers that prevent two species from producing viable, fertile offspring
1. Prezygotic – impede mating between species by hindering the fertilization of ova
2. Postzygotic – impede mating between species by preventing the zygote from developing into a viable, fertile adult
Barriers that prevent different species from interbreeding:
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A summary of reproductive barriers between closely related species
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PREZYGOTIC BARRIERS
a. Habitat Isolation – living in different habitats within same area • Example: snakes in water vs.
landb. Behavioral Isolation – special
signals to attract mates (probably most important barrier)
• Example: fireflies using different blinking signals
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Blue-footed boobies: Males high step as part of a courtship ritual. This creates a behavioral barrier between species.
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c. Temporal Isolation – breeding during different seasons or years• Example: skunks mating in summer vs.
late winterd. Mechanical Isolation – cannot mate due to
anatomical differences• Example: flowers with different
structures for different pollinatorse. Gametic Isolation – gametes unable to fuse
together to make zygote• Example: sperm not surviving vaginal
environment
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POSTZYGOTIC BARRIERSa. Reduced Hybrid Viability – zygotes/embryos
aborted (miscarriage)• Example: frogs (Ranus)
b. Reduced Hybrid Fertility – offspring end up being mostly sterile
• Example: horses mating with donkeys to make sterile mules
c. Hybrid Breakdown – offspring are fertile, but next generation is sterile
• Example: cotton
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FAULTS WITH THE BIOLOGICAL SPECIES CONCEPT
Extinct organisms Asexual organisms Too rigid: dogs and coyotes Gene flow through
subspecies
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OTHER SPECIES CONCEPTS
Morphological – physical features
Recognition – mating adaptations
Cohesion –phenotype (genes and adaptations)
Ecological – live and do (niches)
Evolutionary – sequence of ancestral and descendant populations
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SPECIATION
1. Allopatric – a geographic barrier isolates populations blocking gene flow
2. Sympatric – intrinsic factors alter gene flow (like nonrandom mating)
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Figure 24.6 Two modes of speciation
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ALLOPATRIC SPECIATION
Geographical barriers – mountains forming, canyons forming, climate changing landExample: pupfishes (Cyprinodon) in springs of Death Valley CA and OR (drying caused separated “pools” in which speciation occurred)
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Allopatric speciation of squirrels in the Grand Canyon. On left is Antelope squirrel (A. harris) and on right White-tailed antelope squirrel (A. leucurus)
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Has speciation occurred during geographic isolation?
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Conditions Favoring Allopatric Speciation
Peripheral isolate already different from original population (ex. phenotypic extremes)
Genetic drift at work because smaller population size
Different natural selection in new environment
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SYMPATRIC SPECIATION
Mate choice in two species of Lake Victoria cichlids: females chose mates that have same color as themselves. Under monochromatic light, females chose both colors equally because they look the same. (Nonrandom mating causes sympatric speciation)
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POPULATION GENETICS LEADING TO SPECIATION
Adaptive divergence – when 2 populations adapt to different environments, they accumulate differences in their gene poolsReproductive barriers may evolve coincidentally causing the populations to differentiate into 2 species
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OUTCOMES OF DIVERGENCE
Two populations get back together and interbreed = no new species
Two populations get back together and do not interbreed = 2 new species
Hybrid Zone = where 2 populations get back together and interbreed to make hybrids only around the region where they overlap
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Alleles specific to yellow-bellied toads decrease from 100% in areas where only they are found, to 50% in hybrid area, to almost 0% in fire-bellied area.
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Speciation can occur rapidly or slowly and can result from changes in few or many genes
Punctuated equilibrium – describes periods of apparent stasis “punctuated” by sudden change
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THE HISTORY OF LIFE ON EARTH
CHAPTER 25
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A painting of early Earth showing volcanic activity and photosynthetic prokaryotes in dense mats
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Volcanic activity and lightning associated with the birth of the island of Surtsey near Iceland; terrestrial life began colonizing Surtsey soon after its birth
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INTRODUCTION
Life originated between 3.5 and 4 billion years agoStromatolites – fossilized mats
that contain banded domes of sedimentary rock (3.5 bya) and contain prokaryotes
Oldest rocks are 3.9 billion (Greenland)
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Bacterial mats and stromatolites
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Stromatolites in Northern Canada
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Early Life
To produce simple cells via chemical/physical processes and natural selection:
1. Abiotic synthesis of small organic molecules (ex. amino acids)
2. Joining of smaller molecules into macromolecules (ex. proteins)
3. Packaging macromolecules into protobionts where internal and external environments are different
4. Origin of self-replicating molecules that lead to inheritance
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ABIOTOIC SYNTHESIS OF ORGANIC MONOMERS
A.I. Oparin and J.B.S. Haldane (1920’s) – early atmosphere of earth favored chemical reactions that could produce organic compounds
Low oxygen = a reducing (electron adding) atmosphere
Energy from lightning and higher UV radiation needed to make bonds
Stanley Miller and Harold Urey (1953) – made amino acids from H20, CH4, NH3, H2 and electricity
Now we wonder where this occurred – atmosphere or deep sea vents?
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Lightning
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Proteinoids – proteins formed from abiotic means (no enzymes)Need a substratum like hot
sand, clay, or rockVaporization would concentrate
monomers on substratumMetals in substratum act as
catalysts to bind monomers together
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PROTOBIONTS
Aggregates of abiotically produced molecules
Not capable of precise reproduction, but maintain different internal conditions than external environmentLiposomes – found to form
spontaneously and are made of lipids Can have membrane potential and undergo osmotic pressure
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Laboratory versions of protobionts
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RNA FIRST GENETIC MATERIAL
When a RNA strand is added to a solution of RNA nucleotides, small sequences can be made using strand as template and base pairing
Thomas Cech (1980s) found ribozyme (enzyme that is not a protein) which catalyzes RNA synthesis
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Abiotic replication of RNA
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RNA can make a variety of shapes due to different sequences
This could lead to natural selection of certain shapes (sequences)
Weak binding of amino acids to strand of RNA allows protein to be made (this happens today in rRNA/protein interactions)
Packaging of RNA genes and their products within a membrane a great milestone!
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Origin of life debate
Laboratory experiments prove that life could have evolved in the “primordial soup”, but cannot prove that it did.
First bacteria able to survive extreme heat so life could have evolved near deep sea vents and volcanoes
Extraterrestrial source? Line between protobionts and live cells
blurry
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Radiometric dating – absolute datingHalf-life – the amount of time that it
takes for 50% of the original sample to decay
Carbon-14 has a half life of 5,730 years so its used for younger fossils
Uranium-238 has a half-life is 4.5 billion years so its used for older fossils
Not temperature sensitive
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Radiometric dating
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The Geologic Time Scale
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Clock analogy for some key events in evolutionary history
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GEOLOGIC TIME SCALE
Earth is approximately 4,600,000,000 years old
Precambrian – (4.6 bya to 542 mya) Only bacteria for a billion years Towards end of era there were some
eukaryotes which included algae and soft-bodied invertebrates (some multicellular)
Gradual increase of oxygen caused by photosynthetic bacteria (2.7 – 2.2 bya)
Oxygen revolution followed with great increase in O2. Why? Maybe chloroplasts???
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Endosymbiotic Origin of Mitochondria and Chloroplasts
Larger prokaryotes engulfed smaller prokaryotes (ancestor of mitochondria and chloroplasts) for origin of eukaryotes
Evidence for endosymbiosis Inner membranes of both organelles have ETC
like prokaryotes Both organelles replicate like binary fission,
have ribosomes, and circular DNA like prokaryotes
Many genes move to nucleus (transposons)Eukaryote genome “chimera” like – mixture of
prokaryotic genes and cell parts
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Endosymbiosis
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Paleozoic – (542 – 245 mya) Cambrian explosion of animals
Mostly marine lifeColonization of land by plants
and later animalsFirst amphibians, reptiles and
insectsShallow seasExtinction of marine life at endPangaea formed at end
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Mesozoic – (245 – 65 mya)Flowering plants appearPangaea breaks upSmall mammals appearExtinction of dinosaurs as well as
many other organisms (65mya) Cenozoic – (65 mya – present)
Major radiation of mammalsHumans appear 500,000 years
ago
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HISTORY OF LIFE
Long periods of slow change punctuated by briefer intervals when turnover of species was extensiveMass extinctionsExplosive adaptive radiation
Survivors became adapted to vacant niches left by extinctions
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MASS EXTINCTIONS
Examples: dozen or more in fossil record
Two most studied Permian Extinctions (end of
Paleozoic)Cretaceous Extinctions (end
of Mesozoic)
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Diversity of life and periods of mass extinction
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PERMIAN EXTINCTIONS
Claimed 90% of marine life Occurred in less than 5 million years Possible causes:
Pangaea forming, Siberian volcanoes caused global warming, reduced temperature differences causing low O2 in oceans
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Earth’s crustal plates and plate tectonics (geologic processes resulting from plate movements)
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Crustal plate boundaries
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San Andreas fault
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The history of continental drift
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CRETACEOUS EXTINCTIONS
Claimed half of marine species and most dinosaurs
Possible causes:Continental drift (volcanoes etc.)Asteroid hitting earth on the
Yucatan coast of Mexico Chicxulub crater approximately 180 km in diameter
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Trauma for planet Earth and its Cretaceous life
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Evidence supporting Chicxulub:Thin layer of iridium in rock
layers (from ET debris)Dust cloud blocks sun and
makes acid rainExtinction rates in N. America
more severe and occurred fasterExtinction rates not uniform
across the globe
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Adaptive Radiation
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MAJOR EPISODES 4.6 bya – Origin of earth 4 bya – first prokaryotes Oxygen increases due to
photosynthesis by cyanobacteria (2.7 billion)
2.1 bya - first eukaryotes 1.2 bya – first multicellular
organisms Snowball earth – possible severe
ice age that ended ~570 mya which allowed explosion of life
570 mya – oldest animal fossils
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Some major episodes in the history of life
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Filamentous cyanobacteria from the Bitter Springs Chert
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Fossilized animal embryos from Chinese sediments 570 million years old
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500 mya – plants and symbiotic fungi colonize land
66 mya – dinosaurs extinct 5 mya – apelike humans 500,000 years ago – first
“humans” Animals more like fungi than
plants Most of life on earth has been
aquatic
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Evolution is NOT goal oriented! Evolution is like tinkering—it is a
process in which new forms arise by the slight modification of existing forms
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Fig. 25-25
Recent(11,500 ya)
NeohipparionPliocene(5.3 mya)
Pleistocene(1.8 mya)
Hipparion
Nannippus
Equus
Pliohippus
Hippidion and other genera
Callippus
Merychippus
Archaeohippus
Megahippus
Hypohippus
Parahippus
Anchitherium
Sinohippus
Miocene(23 mya)
Oligocene(33.9 mya)
Eocene(55.8 mya)
Miohippus
Paleotherium
Propalaeotherium
Pachynolophus
Hyracotherium
Orohippus
Mesohippus
Epihippus
Browsers
Grazers
Key
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PHYLOGENY AND THE TREE OF LIFE
CHAPTER 26
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Fossil of a fish: perch
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A gallery of fossils
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Figure 25.1b Skulls of Australopithecus and Homo erectus
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Ammonite
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Figure 25.1f Dinosaur tracks
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Mammoth tusks
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Barosaurus
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VOCABULARY
Phylogeny – evolutionary history of a species or related species
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FOSSIL RECORD Incomplete record Minerals replace organic
material Hard parts leave fossils Some tissues preserved Molds made Relative dating (older
fossils in bottom layers of rock)
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CLASSIFICATION
DomainKingdomPhylumClassOrderFamily
GenusSpecies
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Hierarchical classification
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The connection between classification and phylogeny
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PHYLOGENY V. CLASSIFICATION
Scientific Name = Genus speciesHomo sapiens
Any level is a taxon (pl. taxa)Example: phyla and order etc.
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EVOLUTIONARY HISTORY OF TAXA
Monophyletic – when a single common ancestor gave rise to all species within that taxon (ideal)
Polyphyletic – members of a taxa are derived from 2 or more common ancestors
Paraphyletic – when a taxon excludes species that share a common ancestor
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Monophyletic versus paraphyletic and polyphyletic groups
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Homology – shared likeness due to common ancestry
Analogy – shared likeness due to convergent evolution
Convergent evolution – species from different evolutionary branches may come to resemble each other due to similar ecological roles and natural selection
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Parsimony and the analogy-versus-homology pitfall
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Convergent evolution and analogous structures
The ocotillo of southwestern N. America (left) looks like Alluaudia of Madagascar (right).
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MOLECULAR BIOLOGY AND SYSTEMATICS
Species diverge only when changes occur in nucleotide sequences
Species that are phylogenetically closely related have more similar nucleotide sequences
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MOLECULAR CLOCKS The number of differences in
nucleotide bases between homologous sequences is a measure of evolutionary distance
Clocks calibrated by graphing differences in sequences against known events in fossil recordAssumes constant mutation ratesNatural selection would alter mutation rates
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Dating the origin of HIV-1 M with a molecular clock
• Most widespread strain of HIV
• Estimated to jump to humans in 1930’s
• Based on DNA sequences from 1980 – 1990’s
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FOSSILIZED DNA
Use PCR DNA may be contaminated
with bacterial DNA or other DNA
Even with DNA cloned, cannot make dinosaurs until we understand the developmental steps involved
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PHYLOGENETIC SYSTEMATICS
Phenetics – based on measurable similarities and makes no phylogenetic assumptions
Cladistics – classifies according to the order in time that branches arose along a dichotomous treeClade – an evolutionary branchOutgroup – a species that is
relatively closely related to the group of species being studied, but is clearly not as closely related as any study group members are to each other
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Synapomorphies – shared derived characteristicsCharacteristics that are homologous and evolved in an ancestor that is common to all species on one branch of a fork, but not common to other branch
Parsimony – find the simplest explanation
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Constructing a cladogram
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Cladistics and taxonomy
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Branch lengths can indicate time
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Cladistics accepts only monophyletic taxa Example: birds are more closely related to
crocodiles than snakes and lizard are to crocodiles (birds and crocodiles have synapomorphies not present in snakes and lizards)Class Aves and Class Reptilia wrong
cladistically because birds should be in same group as crocodiles
On other hand both mammals and birds have 4-chambered hearts and yet birds are more closely related to reptiles (not mammals)Four chambered heart evolved more than
once
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Figure 25.18 Modern systematics is shaking some phylogenetic trees (this means class Reptilia in its traditional form is paraphyletic, not monophyletic)
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Figure 25.19 When did most major mammalian orders originate?
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