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Chapter Full

BIO120H1 Chapter Notes - Chapter Full: Gradualism, Pastoralism, Recreation Area


Department
Biology
Course Code
BIO120H1
Professor
James Thomson
Chapter
Full

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Why$Evolution$is$True$–$Jerry$Coyne$
Chapter(1:(What(is(Evolution?(
Life%on%earth%evolved%gradually%beginning%with%one%primitive%species%—%perhaps%a%self9replicating%
molecule%—%that%lived%more%than%3.5%billion%years%ago;%it%then%branched%out%over%time,%throwing%off%
many%new%and%diverse%species;%and%the%mechanism%for%most%(but%not%all)%of%evolutionary%change%is%
natural%selection.%
Evolution’s%six%components:%
1) Evolution%
2) Gradualism%
3) Speciation%
4) Common%ancestry%
5) Natural%selection%
6) Nonselective%mechanisms%for%evolutionary%change%%
“Evolution%is%like%an%architect%who%cannot%design%a%building%from%scratch,%but%must%build%every%
new%structure%by%adapting%a%pre9existing%building,%keeping%the%structure%habitable%all%the%while.”%
Evolution:%a%species%undergoes%genetic%change%over%time%
o Over%many%generations%a%species%can%evolve%into%something%quite%different,%and%those%
differences%are%based%on%changes%in%the%DNA,%which%originate%as%mutations%
Gradualism:%it%takes%many%generations%to%produce%a%substantial%evolutionary%change%
Every%species%goes%back%to%a%single%common%ancestor%%
o So%how%did%the%diversity%today%arise%
Speciation%(splitting):%the%evolution%of%different%groups%that%can’t%interbreed%
o Groups%that%can’t%exchange%genes%
o Species%do%not%have%to%split%
o All%depends%on%if%circumstances%allow%them%to%do%so%
Common%ancestry:%the%flip%side%of%speciation;%we%can%always%look%back%in%time%and%find%
descendants%joining%at%their%ancestors%%
Natural%selection:%explains%apparent%design%in%nature%by%a%purely%materialistic%process%that%doesn’t%
require%creation%or%guidance%by%supernatural%forces%
o Overtime,%population%will%gradually%become%more%suited%to%its%environment%as%helpful%
mutations%arise%and%spread%%
o Deleterious%ones%are%weeded%out%
o Requires%only%that%individuals%of%a%species%vary%genetically%in%their%ability%to%survive%and%
reproduce%
o Natural'selection'is'not'a'master'engineer,'but'a'tinkerer%
o Does%the%best%it%can%with%what%is%has%to%worth%with%
o Natural%selection%does%not%yield%perfection%
! Produces%the%fitter,%not%the%fittest'%
Processes%other%than%natural%selection%can%cause%evolutionary%change%%
A%theory%becomes%a%fact%or%truth%when%so%much%evidence%has%accumulated%in%its%favour%(with%no%
decisive%evidence%against%it)%that%virtually%all%reasonable%people%will%accept%it%%
Testing%evolutionary%theory:%what%Darwin%predicted%to%see%
o Evidence%for%evolutionary%change%in%fossil%record%%
! Deepest%and%oldest%rock%layers%represent%more%primitive%species%
! Younger%and%most%recent%layers%resemble%present9day%species%and%are%more%
complex%
! Should%be%able%to%see%species%changing%over%time%%
o Should%be%able%to%find%some%cases%of%speciation%in%fossil%record%

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! One%line%of%descent%divides%into%two%or%more%
o Should%see%examples%in%species%that%link%together%major%groups%suspected%to%have%common%
ancestry%%
! Missing%links”%%
Should%also%occur%in%layers%of%rock%that%date%to%the%time%when%groups%are%
supposed%to%have%diverged%%
o We%expect%that%species%show%genetic%variation%for%many%traits%%
o Imperfection%is%the%mark%of%evolution,%not%of%conscious%design%%
! We%should%be%able%to%find%some%imperfect%adaptation%%
o We%should%also%see%natural%selection%acting%in%the%wild%%
Chapter(2:(Written(in(the(Rocks(
Fossil%formation%requires%a%very%specific%set%of%circumstances%
o Remains%of%animal%or%plant%must%find%their%way%into%water,%sink%to%the%bottom,%and%get%
quickly%covered%by%sediment%so%that%they%don’t%decay%or%get%scattered%by%scavengers%
Forms%of%life%appear%in%the%record%in%evolutionary%sequence,%then%evolve%and%split%
Transitional'forms:%fossils%that%span%the%gap%between%two%very%different%kinds%of%living%organisms%%
We%only%need%to%produce%fossils%having%types%of%traits%that%link%two%groups%together%
o Also%need%dating%evidence%showing%that%the%fossils%occur%at%the%right%time%in%the%geological%
record%%
o Transitional%species%does%not%equal%ancestral%species%%
o Shows%a%mixture%of%traits%from%organisms%that%lived%both%before%and%after%it%%
Tiktaalik'roseae:%transitional%form%between%fish%and%amphibians%%
o Shows%that%our%ancestors%were%flat9headed%predatory%fish%%
Archaeopteryc'lithographica:%first%link%between%birds%and%reptiles%
o As%fossils%get%younger,%the%reptilian%tail%shrinks,%teeth%disappear,%claws%fuse%together%and%a%
large%breastbone%begins%to%appear%to%anchor%flight%muscles%
Birds%were%predicted%to%have%evolved%from%theropod%dinos%
o Some%do%in%fact%have%feathers%
o Transition%from%thin,%filamentous%body%coverings%to%later%ones%with%distinct%feathers%
o In%bird%evolution,%we%see%refashioning%of%old%features%into%new%ones%
! Forelimbs%with%fingers%and%thin%filaments%on%the%skin%to%fingerless%wings%and%
feathers%
o Bird%ancestor%fossils%are%also%found%demonstrating%bird%like%behaviour%from%today,%ex//%the%
curling%of%the%head%in%the%sleep%position%%
Whales%most%likely%evolved%from%the%hippo%
o As%aquatic%a%land%mammal%can%get%%
o Whales%evolved%from%a%land%mammal%%
Snakes%have%evolved%from%lizard9like%reptiles%that%lost%their%legs%%
o Reptiles%with%legs%appear%BEFORE%snakes%in%the%fossil%record%
The%fossil%record%teaches%us%three%things:%
o Speaks%loudly%of%evolution%
! Confirms%several%predictions:%
Gradual%change%within%lineages%
Splitting%of%lineages%
Existence%of%transitional%forms%%
o Transitional%forms%occur%precisely%where%they%should%
o Evolutionary%change,%even%of%a%major%sort,%nearly%always%involves%remodelling%the%old%into%
the%new%
Doesn’t%make%sense%that%a%celestial%designer%would%make%new%species%by%remodelling%old%ones%

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Chapter(3:(Remnants:(Vestiges,(Embryos(and(Bad(Design(
Organisms%are%palimpsests%of%history%–%evolutionary%history%
o Palimpsests%were%manuscripts%that%were%scraped%and%used%again%
Vestiges:%a%feature%of%a%species%that%was%an%adaptation%in%its%ancestors%but%has%either%lost%its%
usefulness%completely%or%has%been%co9opted%for%new%used%
o REMEMBER,%it%is%vestigial%not%because%it’s%functionless,%but%because%it%no'longer'performs'
the'function'for'which'it'evolved'%
o Examples:%wings,%our%appendix,%the%coccyx%
Atavisms:%the%reappearance%of%an%ancestral%trait%
o Humans%born%with%tails,%horses%extra%toes,%whales%with%a%random%limb%%
Dead'genes:%genes%once%useful%but%are%no%longer%intact%or%expressed%%
o Silenced%genes%
o Ex//%GLO%in%humans%
! No%longer%need%it%because%we%obtain%vitamin%C%from%our%diet%%
! We%don’t%eat%leaves%and%cannot%breakdown%cellulose%
Why%do%species%have%the%fish%embryo%stage%of%development?%
o Some,%like%humans,%don’t%need%fish%gill%arches%or%a%fish%circulatory%system%
o The%answer%involves%recognizing%that%as%one%species%evolves%into%another,%the%descendant%
inherits%the%development%program%of%its%ancestor%
! All%the%genes%that%form%ancestral%structures%%
The%“adding%new%stuff%onto%old”%principle%also%explains%why%the%sequence%of%development%changes%
mirrors%the%evolutionary%sequence%of%organisms%%
As%one%group%evolves%from%another,%it%often%adds%to%the%development%program%%
Ernst%Haeckel:%“biogentic%law”%in%1866%
o Ontogeny'recapitulates'phylogeny'%
o The%development%of%an%organism%simply%replays%its%evolutionary%history%%
o Largely%disputed,%Haeckel%was%accused%of%making%embryo%drawings%more%similar%than%they%
really%are%
Embryos%still%show%a%form%of%recapitulation%
o Features%that%arose%earlier%in%evolution%often%appear%earlier%in%development%
o Only%makes%sense%if%species%have%evolutionary%history%
Bad%design%occurs%in%numerous%organisms%
o No%such%things%as%perfect%design,%that%would%require%an%intelligent%designer%
o If%evolution%were%true,%then%why%would%a%designer%cause%imperfections?%
Imperfect%design%is%the%mark%of%evolution%
o Ex//%laryngeal%nerve%of%mammals%
! Evolved%from%fish%
! Could%not%find%a%way%around%the%heart%(?)%so%was%pushed%farther%back%and%elongated%
! Inefficient%%
! Prone%to%damage%if%chest%area%is%affected%
o Ex//%male%testes%in%humans%
! Design%of%urethra%runs%through%middle%of%prostate%gland%that%produces%seminal%fluid%
! It’s%a%sewage%pipe%running%directly%through%a%recreation%area”%
! Many%males%develop%enlarged%prostates%which%squeeze%urethra%and%make%urination%
painful%and%difficult%
o Ex//%human%birth%
! Extremely%painful%unlike%many%other%organisms%
A%designer%may%have%motives%unfathomable,%but%the%particular%bad%designs%only%makes%sense%if%
they%evolved'from'features'of'earlier'ancestors'%
%
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