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The Basis ofEvolution

There is grandeur in this view of life, with its severalpowers, having been originally breathed into a few

forms or into one; and that, whilst this planet has

gone cycling on according to the fixed law of gravity,

from so simple a beginning endless forms mostbeautiful and most wonderful have been, and are

being, evolved.

-- Charles Darwin

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Whats the Big Idea?

Descent with Modification

organisms are altered through descent

from an ancestor that lived in the remote

past

Environments change Species change

Lecture 1-19 (HHMI) 19.3

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Descent with Modification is like a tree with

multiple branching points from a commontrunk to the tips of the youngest twigs that

represent the diversity of living organisms

Hyracoidea(Hyraxes)

Sirenia

(Manateesand relatives)

Yearsago

Millionsofyea

rsago D

einotherium

Mammut

Stegodon

Mammuthus

Platybelodon

Barytherium

Moeritherium

Elephasmaximus

(Asia)

Loxodontaafricana

(Africa)

Loxodontacyclotis

(Africa)

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Homology

Homology

Is the study of similar structures in

different species due to their ancestry

19.5

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Anatomical Homologies Homologous structures are anatomical similarities

that represent variations of a structure that was

present in a common ancestor

Human Cat Whale Bat

19.5

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Homology in embryology (study of development)

Reveals additional anatomical similaritiesnot visible in adult organisms

Pharyngeal

pouches

Post-anal

tail

Chick embryo Human embryo

19.5

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Vestigial organs

Are remnants of structures that served

important functions in the organismsancestors

Lettercin the picture indicates the undeveloped hind

legs of a baleen whale.19.5

http://upload.wikimedia.org/wikipedia/commons/f/f3/Cyst_-_wisdom_tooth.jpghttp://upload.wikimedia.org/wikipedia/commons/5/54/Skelett_vom_Wal_MK1888_ohne_Text.gif

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Genetic homologies

Are generally reflected in their molecules,

their genes, and their gene products

Species

Human

Rhesus monkey

Mouse

Chicken

Frog

Lamprey14%

54%

69%

87%

95%

100%

Percent of Amino Acids That Are

Identical to the Amino Acids in a

Human Hemoglobin Polypeptide

19.5

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Gene sequence conservation in

hemoglobin

Human

Chimp Rat

Mouse

Chicken

Coding Coding Coding

INTRON

EXONS

Genome Browser19.5

http://genome.ucsc.edu/cgi-bin/hgc?hgsid=91487431&o=5210994&t=5212620&g=mzPt1Mm3Rn3Gg2_pHMM&i=mzPt1Mm3Rn3Gg2_pHMM&c=chr11&l=5210994&r=5212620&db=hg16&pix=620http://genome.ucsc.edu/cgi-bin/hgc?hgsid=91487431&o=5210994&t=5212620&g=mzPt1Mm3Rn3Gg2_pHMM&i=mzPt1Mm3Rn3Gg2_pHMM&c=chr11&l=5210994&r=5212620&db=hg16&pix=620

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Whats the Big Idea?

Natural Selection

The preservation of favorable variations

and the rejection of injurious variations I

call Natural Selection

-- Charles Darwin

19.1-3

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Whats needed for Natural

Selection? Variation differing characteristics

Adaptation - characteristics that offer asurvival/reproductive advantage

Selection favoring or rejection of

certain characteristics

Time TIME (thousands/millions of years)

Lecture 1-26 (HHMI) 19.1

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Observation #1: Many more offspring

are produced than survive for each

species Observation #2: Nonetheless,

populations tend to be stable in size

Observation #3: Populations of specieshave limited resources

Inference #1: There is a struggle forexistence among individuals of a

population, with only a fraction of their

offspring surviving19.4

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Observation #4: Members of a

population vary extensively in theircharacteristics

Observation #5: Much of this variation

is heritable

19.4

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Inference #2: Survival depends in part on

inherited traits. Individuals whose inheritedtraits give them a high probability of

surviving and reproducing are likely to leave

more offspring than other individuals. Inference #3: This unequal ability of

individuals to survive and reproduce will

lead to a gradual change in a population,with favorable characteristics becoming

more common (natural selection).

19.4

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Artificial Selection

Human (not nature) directed Demonstrates that selecting variations

can alter form over time

19.6