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7/19/2019
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BI 102 Lecture 13:Natural Selection
Early Biological and Geological Thought
• Before the scientific method, understanding of the world was based largely on observation
• Observation was limited• People rarely traveled more than 20 miles from where they were born• Limited interaction with people, ideas, landscapes, or species outside that
radius• Sometimes misunderstood the observations
• Example: alchemy
Early Biological and Geological Thought
• Prevailing thought was that the Earth and life on it are static• The Earth has always existed in its present form• All species were created simultaneously in their present form• Neither change over time
Early Biological and Geological Thought
• Many had attempted to classify living things• Perhaps the most famous early
attempt was Aristotle’s Ladder of Nature
• Organisms exist in a linear hierarchy of complexity
• Do not change
Early Biological and Geological Thought
• The age of European exploration (~1450-1800) changed everything• The world was established as spherical, not flat• Transportation by sea made travel to distant lands faster, safer
• Allowed for the exchange of goods and ideas at an unprecedented rate
Early Biological and Geological Thought
• The European discovery of the western hemisphere revealed the staggering biological and geological diversity on the planet
• Explorers drew pictures, collected specimens• Brought knowledge back, spread to other areas of the world• Everyone started asking questions about the nature of the Earth and life on it• Many new ideas were proposed
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Early Biological and Geological Thought
• Georges Cuvier (late 1700s – early 1800s)• Considered the father of modern paleontology• Observed that fossils were different in different rock layers• Proposed the idea of catastrophism
• The Earth is relatively young (~10,000 years old)• Largely shaped by catastrophic events• Catastrophic events cause mass extinction• Species are replaced by new ones
Early Biological and Geological Thought
• Charles Lyell (early to mid 1800s)• Proposed uniformitarianism
• The Earth is much older• Shaped by slow, gradual forces• Same forces are still at work today
• Limited his work largely to geological thought, but became a major influencer in contemporary biological thought
Early Biological and Geological Thought
• Jean Baptiste Lamarack (late 1700s – early 1800s)• Believed that species do change over time• First to propose a cohesive theory of biological evolution
• All species possess an innate drive for perfection• Alchemical processes drive organisms up a ladder of complexity• Environmental forces adapt species through use and disuse
• Inheritance of acquired characteristics
Early Biological and Geological Thought
• Thomas Malthus (late 1700s – early 1800s)• Economist and scholar• First to use the term “survival of the fittest”• Observed that prosperity leads to population growth• Population growth leads to wealth disparity and the
suffering of the poor• The poor then die, reducing the population and increasing
the prosperity of those who remain• Increased prosperity leads to population growth• “Malthusian Trap”
Modern Biological and Geological Thought
• Modern thought regarding changes in living things over time are based on works from the mid 1800s by two naturalists
• Alfred Wallace• Charles Darwin
Charles Darwin
• Charles Darwin – a smart man, but a bad student• Attended a year of medical school and was interested in anatomy, but
neglected his studies to learn taxidermy• Was sent to a different college to become a cleric,
but neglected his studies in favor of riding, shooting, and beetle collecting
• Graduated 10th in his class in “ordinary studies”
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Charles Darwin
• Recommended by his former mentor to accompany Robert FitzRoyaboard the HMS Beagle
• Expedition to chart the coastline of South America• Self-funded naturalist position• A real disappointment to his father
Voyage of the HMS Beagle – 1831-1836
• Packing list12 shirts1 carpet bag1 pair slippers1 pair of light walking shoes1 microscope (a single lens model by Bancks & Son, London)1 geological compass1 plain compass2 pistols (with spare parts)1 rifle (with spare parts)1 telescope1 pencil case1 geological hammer5 simisometers3 mountain barometers1 clinometer1 camera obscura1 hygrometer (belonged to FitzRoy)1 taxidermy book2-3 Spanish language books14 other books, including Humboldt's "Personal Narrative" and Lyell’s "Principles of Geology Vol. 1"1 coin purse (Fanny Owen's gift)1 pin with a lock of Sarah Owen's hair (Fanny's sister)
Charles Darwin
• Spent nearly 5 years sketching, collecting specimens, and theorizing• Sent specimens, journals, and letters at intervals back to Cambridge• Returned a scientific celebrity
• Continued his work for the next 20 years, meeting with Lyell andothers to develop his theories on evolution
Elements of Darwin’s Theory of Evolution
• Darwin’s theory has 2 main postulates1) Descent with modification2) Adaptation by natural selection
Elements of Darwin’s Theory of Evolution
• Postulate 1: Descent with modification• Variation exists within a population• At least some of these variations are heritable
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Elements of Darwin’s Theory of Evolution
• Postulate 2: Adaptation by natural selection• Not all individuals in a population will survive and reproduce
• High reproductive effort• Limited resources• Unequal reproductive success
Elements of Darwin’s Theory of Evolution
• Postulate 2: Adaptation by natural selection• Not all individuals in a population will survive and reproduce• Survival and reproduction are not random
• Those with favorable traits leave more offspring• “Survival of the fittest”
• Favorable traits accumulate within a population• Population is modified over time
• Evolution
Natural Selection
• Adaptation by natural selection has nothing to do with effort• It does not give an organism what it “needs”• An advantage must be heritable in order for it to be passed on to
offspring• Ultimately the result of mutations in the gametes that provide an advantage
Natural Selection
• Natural selection is not random• Traits are produced by chance mutations, but only
persist if they provide an advantage in theorganism’s environment
(Note: Random events do occur that change the patterns of inheritance, but that is not natural selection. We will discuss this later.)
Natural Selection
• Question• There is great natural variation in the skin color of frogs• None of the frogs below is poisonous• Which one will be more likely to survive and reproduce?
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Natural Selection
• What is the evidence for natural selection?• Fossil record• Comparative anatomy• DNA homology• Pseudogenes• Artificial selection• Observations• Experimental evidence• Convergent evolution
Evidence for Natural Selection
• Fossil record• Fossils in older strata don’t look much like species from today• Fossils in newer strata do• Provides a timeline for how species have changed
Youngestrocks
Oldestrocks
Evidence for Natural Selection
• Fossil record• Example: evolution of the horse
Hyr
acot
heriu
m
Oro
hipp
us
Epi
hipp
us
Mes
ohip
pu
s
Anc
hith
eriu
m
Mio
hipp
us
Meg
ahip
pu
s
Hyp
ohip
pu
s
Eocene
Oligocene
Miocene
browsersgrazersmixed feeders
Kal
oba
tipp
us
Arc
haeo
hip
pus
Des
mat
ippu
s
Par
ahip
pus
Mer
ychi
ppus
Pse
udhi
pp
ario
n
Neo
hipp
ario
n
Hip
pari
on
Nan
nipp
us
Cor
moh
ippa
rio
n
Pro
tohi
ppu
s
Cal
ippu
s
Plio
hipp
us
Ast
rohi
ppu
s
Ono
hip
pidi
on
Din
ohip
pus
Equ
us
Merychippus(mixed feeders)
Neohipparion(grazers)
Nannippus(grazers)
Equus(grazers)
Anchitherium(browsers)
Hyracotherium(browsers)
Mesohippus(browsers)
Pleistocene
5MYA
10MYA
15MYA
20MYA
25MYA
30MYA
35MYA
40MYA
45MYA
50MYA
55MYA
60MYA
Pliocene
55 mya 40 mya 20 mya 17 mya 14 mya 12 mya 5 mya
Evidence for Natural Selection
• Fossil record• Transitional fossils
• Fossils that show links between different groups of modern species• Reptiles to birds
Caudipteryx – 125 myaArchaeopteryx – 145 mya
Evidence for Natural Selection
• Fossil record• Transitional fossils
• Fossils that show links between different groups of modern species• Water to land
Tiktaalik – 375 mya
Lobed-finned fish - modern
Evidence for Natural Selection
• Fossil record• Transitional fossils
• Fossils that show links between different groups of modern species
• Land back to the water
Modern toothed whales
Rodhocetus swam withan up-and-down motion. 47 mya
Ambulocetusprobably walked on land. 49 mya
Pakicetus attocki lived on land. 55 mya
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Evidence for Natural Selection
• Comparative anatomy• Modern species share considerable anatomy with each other, and with
ancient species• Example: vertebrate forelimbs
Pterodactyl
Bird
Bat
Dolphin
Seal
Dog
Sheep Shrew
humerus
ulna
metacarpalsphalanges
radiuscarpals
Human
GRASPINGRUNNINGSWIMMINGFLYING
Evidence for Natural Selection
• Comparative anatomy• Modern species share considerable anatomy with each other, and with
ancient species• Example: vestigial structures
Evidence for Natural Selection
• Comparative anatomy• Modern species share considerable anatomy with each other, and with
ancient species• Example: embryonic development
Evidence for Natural Selection
• DNA homology• Modern species have a considerable amount of DNA in common• How much DNA do you think humans share with these species?• Let’s just look at one gene
Evolutionary relationships based on DNA and protein sequence -Cytochrome C amino acid differences
0
1
1011
13
1728
Evidence for Natural Selection
• Pseudogenes• Genes that are still present in a species, but no longer functional• Example: vitamin C synthesis
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Evidence for Natural Selection
• Pseudogenes• Genes that are still present in a species, but no longer functional• Example: olfactory genes in mammals
DogMouseRatHuman
1,1001,5001,500900
18%20%19.5%63%
Total # of olf. genes % dead
Evidence for Natural Selection
• Artificial selection• Humans have been selecting for desirable traits in plants, animals, yeast, and
bacteria for millenia• Organisms with favorable traits were bred to others with favorable traits• Has led to astounding variety within species in a relatively short period of
time
Evidence for Natural Selection
• Artificial selection• Example: Brassica family of vegetables
Evidence for Natural Selection
• Artificial selection• Example: Teosinte grass vs. modern corn
Teosinte
Maize
Evidence for Natural Selection
• Artificial selection• Example: Domestic dogs
Evidence for Natural Selection
• Observations• Example: Peppered moth
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Evidence for Natural Selection
• Observations• Example: Antibiotic resistance
Evidence for Natural Selection
• Observations• Example: Sickle cell anemia
Evidence for Natural Selection
• Experimental evidence• Example: Brown anole
• Native to Iron Cay, a forested island in the Bahamas• Released in small numbers onto 7 bush-covered islands in 2005 after a
hurricane wiped out the native lizard population• Also released onto 12 forested islands nearby
Evidence for Natural Selection
• Experimental evidence• Example: Brown anole
• Forests favor long hind limbs• Brush favors shorter hind limbs• All anoles had similar hind limb length at the beginning of the
experiment• What would happen over time?
Evidence for Natural Selection
• Experimental evidence• Example: Brown anole
• Lizards on brush-covered islands had shorter hind limbs after several generations
• Lizards on forested islands still had long hind limbs
Evidence for Natural Selection
• Convergent evolution• Natural selection allows for the persistence of traits that provide an
advantage in a particular environment• If similar environments exist in different places, we would expect similar traits
to develop in the species there• Similar selection pressures produce similar results
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Evidence for Natural Selection
• Convergent evolution• Example: Placental mammals vs. marsupials
Wolf
Thylacine
Flying squirrel
Flying phalanger
Niche Burrower
Mole
Lesser anteater Ring-tailed lemur Ocelot
Spotted cuscus
Numbat
Marsupial mole
Anteater Climber Glider
Marsupialmouse
AustralianMarsupials
PlacentalMammals
NocturnalInsectivore
Grasshoppermouse
StalkingPredator
ChasingPredator
Tasmanianquoll
Evidence for Natural Selection
• Convergent evolution• Example: Primates in Madagascar vs continental Africa
Evidence for Natural Selection
• Convergent evolution• Example: Echolocation in the bottlenose dolphin and bats
• Similar mutations in the Prestin gene, which is required for hearing in mammals
• Both share the ability, even though their common ancestors did not
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