Notes Lecture 13 BI 102 Natural Selectioncf.linnbenton.edu/mathsci/bio/waitea/upload/Notes...Notes Lecture 13 BI 102 Natural Selection ... a

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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


• 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


• 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


• 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


• 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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• 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


• 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


• 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


• 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


• Postulate 1: Descent with modification• Variation exists within a population• At least some of these variations are heritable

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• Postulate 2: Adaptation by natural selection• Not all individuals in a population will survive and reproduce

• High reproductive effort• Limited resources• Unequal reproductive success


• 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


• Fossil record• Example: evolution of the horse

Hyr

acot

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Oro

hipp

us

Epi

hipp

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Mes

ohip

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s

Anc

hith

eriu

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Mio

hipp

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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

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ario

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Neo

hipp

ario

n

Hip

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on

Nan

nipp

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Cor

moh

ippa

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Pro

tohi

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Cal

ippu

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Plio

hipp

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Ast

rohi

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Ono

hip

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Din

ohip

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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


• Fossil record• Transitional fossils

• Fossils that show links between different groups of modern species• Reptiles to birds

Caudipteryx – 125 myaArchaeopteryx – 145 mya



• Fossils that show links between different groups of modern species• Water to land

Tiktaalik – 375 mya

Lobed-finned fish - modern



• 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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• 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



ancient species• Example: vestigial structures



ancient species• Example: embryonic development


• 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


• Pseudogenes• Genes that are still present in a species, but no longer functional• Example: vitamin C synthesis

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• 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


• 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


• Artificial selection• Example: Brassica family of vegetables


• Artificial selection• Example: Teosinte grass vs. modern corn

Teosinte

Maize


• Artificial selection• Example: Domestic dogs


• Observations• Example: Peppered moth

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• Observations• Example: Antibiotic resistance


• Observations• Example: Sickle cell anemia


• 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



• 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?



• Lizards on brush-covered islands had shorter hind limbs after several generations

• Lizards on forested islands still had long hind limbs


• 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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• 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


• Convergent evolution• Example: Primates in Madagascar vs continental Africa


• 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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Notes Lecture 13 BI 102 Natural Selectioncf.linnbenton.edu/mathsci/bio/waitea/upload/Notes...Notes Lecture 13 BI 102 Natural Selection ... a

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