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HomininEvolutionOverview

GenotypeandPhenotype:-Eachindividualhasagenotype(whichgenestheyhave)andaphenotype(thewayinwhichthosegenesareexpressed)-Somephenotypictraitswillbebeneficialforsurvival,somewillbeneutral,andotherswillbemaladaptive.Individualswithmaladaptivephenotypictraitswilltendtodieoffsooner,andindividualswithbeneficialtraitswillstickaroundtosuccessfullyreproduce.-Individualswhoexhibithigherfitness(abletoreachreproductiveageandreproduce)willbemoresuccessfulinpassingtheirgenesontothenextgenerationthroughnaturalselection-Overtime,theprevalenceofvariousgenesinthepopulationwillchangeàEVOLUTION!SettheScene:-Around6.5millionyearsago,therewasahuman-chimplastcommonancestor(LCA)fromwhomallhomininsevolved-ThisLCAwouldhaveabrainandbodyaboutthesizeoftheape.Itwouldhavehadlongarmsandcurvedfingers,whichwouldhaveallowedittomorearoundthetreestoforageforfood.Itwouldhavehadlargercaninesthanthoseseeninmodernhumansandthemaleswouldhavelikelybeenlargerthanthefemales(andalsohadlargercanines).AlthoughthisLCAwouldhavebeencomfortablemovingthroughoutthetrees,itsmainmodeoflocomotionwouldhavebeenterrestrialquadrapedalism(walkingonthegroundonallfours).Itsdietwouldhaveconsistedprimarilyoffruitsandleaves.Australopithecus(EastandSouthAfrica):-Around4millionyearagowefindtheearliesthominins—membersofthegenusAustralopithecus.Thesewereterrestrialbipeds(walkedontwolegsontheground)butsometimestooktothetreestoforageorforprotection.-RaymondDartdiscoveredthefirstspecimensofAustralopithecusin1924(Dart,1925).Sincethen,hundredsoffossilsfromseveralspecieshavebeendiscovered.WenowknowthatAustralopithecuswasahighlysuccessfulgenusthatpersistedfornearlythreemillionyears.-Theywereclearlyfullybipedal,meaningthattheywereadaptedforwalkingarounduprightontheground.Traitsthatfacilitatedeffectivebipedalgaitwerebeingselectedfor(shortbowl-shapedpelvis,craniumdirectlyontopofthespine,bigtoeinlinewithothertoes,etc.).Theirbrainswereroughlythesizeofmodernchimpsandgorillasdespitehavingafairlysmallbodysize(approximately65lbs.adultfemalesand85lbs.foradultmales)(McHenry,1992).Theircanineswerenotasprominentasthoseoftheirlastcommonancestor.-Thismixedterrestrial(ontheground)&arboreal(inthetrees)strategywouldhaveservedthesespecieswellinthemixedwoodlandandsavannahenvironmentstheyinhabited.


Paranthropus:-Someaustralopithshadhighlyspecializedmorphologyasaresultoftheirenvironment.-SpeciesinthegenusParanthropushadextremelylargechewingmusclesandbigteethinordertoeathard,lowqualityplantfoodsthatrequiredpowerfulchewingtoprocess.-MostAustralopithecusspecieswereextinctby2millionyearsago,butsomerobustformspersistedinEastandSouthAfricauntilabout1.2millionyearsago.Australopithecusvs.Paranthropus:-Originallygroupedtogether(moreofa“lumper”approach),aethiopicusandboiseiwerethoughttobemorerobustformsofAustralopithecus.Eventually,scientistsrecognizedthatthe'robust'formsweredifferentenoughtobeintheirownspecies.Usingmoreofa“splitter”mentality,thefossilswererecognizedasbeingdifferentenoughfromtheotheraustralopithecines-andsimilarenoughtoeachother-tobeplacedintoaseparategenus.ThisnewgenuswascalledParanthropus.TheGenusHomo:-Theearliestfossilsofourowngenus,Homo,datefromabout2.3millionyearsago(Kimbeletal.1997).TheseearlyspecimensaresimilarinbrainandbodysizetoAustralopithecus,butshowdifferencesintheirmolarteeth,suggestingachangeindiet.-TheoldestmemberofourspeciesisH.habilis(2.3–1.4mya).AnthropologistscallH.habilisthe“handyman”becausethereisevidencethattheyusedstonetools.Thiswouldhaveaddedmeatandbonetotheirpreviouslyexclusively-plant-based-diet.-H.rudolfensis(1.9mya)isverysimilartoH.habilisexceptithasaconsiderablylargercranialcapacity(brainsizerelativetobodysize),alongerface,andlargerteeth.ItslongfaceandlargerteethmakeitsimilartotheAustralopithsbutitslargercranialcapacitygroupeditintothegenusHomo.-H.erectus(1.9mya–100kya),themorewidespreaddescendentofH.habilis,livedthroughoutAfricaandEurasia(Anton,2003).-H.erectusnolongerhasthearborealupperlimbadaptationsasseeninAustralopiths.Theyhaveanincreasedcranialcapacityandareductioninthesizeoftheteeth.Thismostlikelyreflectsincreasingrelianceinsocialinteractionandcommunicationaswellasasofter,richerdiet.-Around700kya,H.erectusinAfricagaverisetoH.heidelbergensis,aspeciesverysimilartomodernhumansintermsofbodyproportions,dentaladaptations,andcognitiveability(Rightmire,2009).H.heidelbergensis,wasanactivebig-gamehunter,producedsophisticatedstonetools,andhadcontroloffire(RoebroeksandVilla,2011).-Neanderthals(H.neanderthalensis)arehomininswithstockyphysiques,complexbehaviors,andbrainssimilarinsizetoours.TheyarethoughttohaveevolvedfromH.heidelbergensispopulationsinEuropebyatleast250kya(Rightmire,2008;Hublin,2009).ThereisnowsufficientevidencethatweinterbredwithNeanderthalsandmanyofuscarrysomeoftheirgenesinourowngeneticmakeupstoday(Greenetal.,2010)!


-FossilandDNAevidencesuggestourownspecies,H.sapiens,evolvedinAfrica200kya(Relethford,2008;Rightmire,2009),probablyfromH.heidelbergensis.Ourspecieshaslargebrains,exhibitscomplexbehaviorssuchascooperativehunting,tooluse,andevenabstractthought.H.sapienseventuallyleftAfricanandpopulatedtheglobe.-NewdiscoverieslikeH.naledi(900kya)showusthatwedon’tknoweverythingyetabouthowwecametobe!Thesesmallhomininsdemonstratea“mosaicoftraits”despitebeingfairlyyoung!Wedon’treallyknowwhatthismeansyet…Paleoanthropologistsstillhavealottolearn!WhyThisTrendTowardsLargerBrains?-Bigbrainsarethoughttobebeneficialforthedevelopmentanduseoftools,insocialbehavior,andasameansofadaptationtotheenvironment.-Accordingtothesocialbrainhypothesis,brainsize(specificallytheneocortex)isimportantwhenconsideringsocialbehaviorandgroupsize.Theneocortexiswhatgivesustheabilitytounderstandwhatothersarethinking.Considerthefollowinglineofevidence:Individualswithlargerbrainsaremoresuccessfulsocially,thustheyhaveincreasedfitness(havemorekids),thustheypasstheirgenesofftotheiroffspring.BUT,inorderforthistobetruetheremustbeastrongselectionpressuretomovepopulationtowardslargerbrainsizesincebigbrainsarecaloricallyexpensive!Thisoverviewhasbeenadaptedfromthefollowingsources:Alexeev,V.P.,1986.TheOriginoftheHumanRace.Moscow,Progress Publishers.Wood,B.,Collard,M.,1999.ThechangingfaceofgenusHomo.Evolutionary Anthropology8,195-207.Pontzer,H.(2012)OverviewofHomininEvolution.NatureEducation Knowledge3(10):8AdditionalSources:Anton,S.C.NaturalhistoryofHomoerectus.AmericanJournalofPhysical AnthropologyS37,126-70(2003)Blumenschine,R.J.etal.LatePlioceneHomoandhominidlandusefromWestern OlduvaiGorge,Tanzania.Science299,1217-12121(2003)Brunet,M.etal.NewmaterialoftheearliesthominidfromtheUpperMioceneof Chad.Nature434,752-755(2005)Dart,R.A.Australopithecusafricanus:thesouthernape-manofAfrica.Nature115, 195-199(1925)DeGiorgio,M.etal.OutofAfrica:modernhumanoriginsspecialfeature:explaining worldwidepatternsofhumangeneticvariationusingacoalescent-based serialfoundermodelofmigrationoutwardfromAfrica.PNASUSA106, 16057-16062(2009)


Falk,D.etal.Earlyhominidbrainevolution:anewlookatoldendocasts.Journalof HumanEvolution38,695-717(2000)Green,R.E.AdraftsequenceoftheNeandertalgenome.Science328,710-722Harcourt-Smith,W.E.&L.C.Aiello.Fossils,feetandtheevolutionofhumanbipedal locomotion.JournalofAnatomy204,403-416(2004)Hublin,J.J.TheoriginofNeanderthals.PNAS45,169-177(2009)Kimbel,W.H.etal.SystematicassessmentofamaxillaofHomofromHadar,Ethiopia.AmericanJournalofPhysicalAnthropology103,235-262(1997)Kunimatsu,Y.etal.AnewLateMiocenegreatapefromKenyaanditsimplications fortheoriginsofAfricangreatapesandhumans.PNASUSA104,19661- 19662.(2007)McHenry,H.M.Bodysizeandproportionsinearlyhominids.AmericanJournalof PhysicalAnthropology87,407-431(1992)Pickford,M.etal.BipedalisminOrrorintugenensisrevealedbyitsfemora.Comptes RendusPalevol1,1-13(2002)Pontzer,H.(2012)OverviewofHomininEvolution.NatureEducation Knowledge3(10):8Relethford,J.H.Geneticevidenceandthemodernhumanoriginsdebate.Heredity 100,555-563(2008)Rightmire,G.P.OutofAfrica:modernhumanoriginsspecialfeature:middleand laterPleistocenehomininsinAfricaandSouthwestAsia.PNASUSA106, 16046-16050(2009)Rightmire,G.P.HomointheMiddlePleistocene:Hypodigms,variation,andspecies recognition.EvolutionaryAnthropology17,8-21(2008)Roebroeks,W.&P.Villa.OntheearliestevidenceforhabitualuseoffireinEurope. PNASUSA(2011)Senut,B.etal.FirsthominidfromtheMiocene(LukeinoFormation,Kenya).C.R. Acad.Sci.Paris,SciencesdelaTerreetdesplanètes/EarthandPlanetary Sciences332,137-144(2001)Ward,C.V.etal.Completefourthmetatarsalandarchesinthefootof Australopithecusafarensis.Science331,750-753(2011)Ward,C.V.InterpretingthepostureandlocomotionofAustralopithecusafarensis: wheredowestand?AmericanJournalofPhysicalAnthropologyS35,185- 215(2002)White,T.D.etal.Ardipithecusramidusandthepaleobiologyofearlyhominids. Science326,75-86(2009)Young,N.M.etal.ThephylogeneticpositionofMorotopithecus.JournalofHuman Evolution46,163-184(2004)Zollikofer,C.P.etal.VirtualcranialreconstructionofSahelanthropustchadensis. Nature434,755-759(2005)


SupplementalMaterial:HumanEvolutionFamilyTree

Image credit: © 2012 Nature Education https://www.nature.com/scitable/knowledge/library/overview-of-hominin-evolution-89010983 The human evolutionary family tree. Relationships and estimated divergence times of the living apes are shown. Hominins are all species, including side-branches and extinct species, on the human line (highlighted) after our Last Common Ancestor with chimpanzees & bonobos (marked “A”). Some fossil hominin species are shown in the right-hand column, with their approximate age ranges indicated; early hominins: gray, Australopithecus: blue, Homo: orange.


Image credit: Francis Thackeray, University of Witwatersrand in Johannesburg: http://www.faz.net/aktuell/wissen/woher- kommt-der-mensch-1-unser-stammbaumim-mathe-style-14538823- p2.html?printPagedArticle=true#pageIndex_2


Image credit: S. V. Medaris / UW-Madison http://www.sci-news.com/othersciences/anthropology/science-homo-naledi-03224.html


SupplementalMaterial:Reconstructions

Australopithecus africanus

Reconstruction based on AL444-2 by John Gurche http://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-africanus


Australopithecus sediba

http://ngm.nationalgeographic.com/2011/08/malapa-fossils/fischman-text


Paranthropus boisei

Reconstruction based on OH 5 and KNM-ER 406 by John Gurche http://humanorigins.si.edu/evidence/human-fossils/species/paranthropus-boisei


Paranthropus aethiopicus

Reconstruction by Roman Yeveyev https://i.pinimg.com/originals/75/7b/7a/757b7a01c6d9661c0a9e436bf066c937.jpg


Homo habilis

Reconstruction by John Gurche - National Geographic Magazine Oct, 2015 http://evolution-involution.org/habilis_rudolfensis_erectus_gurche.jpg


Homo rudolfensis

Reconstruction by John Gurche - National Geographic Magazine Oct, 2015 http://evolution-involution.org/habilis_rudolfensis_erectus_gurche.jpg


Homo erectus

Reconstruction based on ER 3733 by John Gurche http://humanorigins.si.edu/evidence/human-fossils/species/homo-erectus


Homo heidelbergensis

Reconstruction based on Kabwe by John Gurche http://humanorigins.si.edu/evidence/human-fossils/species/homo-heidelbergensis


Homo neanderthalensis

Reconstruction based on Shanidar 1 by John Gurche http://humanorigins.si.edu/evidence/human-fossils/species/homo-neanderthalensis


Homo sapiens

http://www.nhm.ac.uk/discover/how-we-became-human.html


Homo naledi

Reconstruction by John Gurche and Mark Thiessen http://www.sci-news.com/othersciences/anthropology/science-homo-naledi-03224.html