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8/14/2019 Basis Of the Evolution
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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.gif8/14/2019 Basis Of the Evolution
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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=6208/14/2019 Basis Of the Evolution
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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
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