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Motivation

Homeostasis

Stabilityinbodystatemaintainedthroughself-regulationInvolvessetpointsE.g.,98.6degreesF

Hunger

•  Exampleofadrivestate– Stateofinternaltension– Thesystembehavessoastoreducethetension

•  Determinedbyacomplexsetofsignals– Manyinvolvingtheendocrinesystem(hormones)– E.g.,fatcellssecreteleptinwhenfull,andleptinsuppressesappetite

•  Signalsaremonitoredandintegratedbythehypothalamus

Someappetite-relatedsignals

LeptinfromfatcellsGlucose

readings

Cognitive,emotional(e.g.,depression)Sensory

Nutrientreadings

Neural

Hormonal

(“mastergland”)

Weightsetpoints

•  Weallhaveaweightthatiseasytomaintain–  Increasesapoundortwoayear,onaverage

•  Whenweloseweight,ourmetabolismslows– Keepsusalivewhenfoodisscarce•  Exampleofanegativefeedbackloop

–  Ifyougainagain,yourmetabolismmaystaylow– Makingitdifficulttokeeptheweightoff

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nytimes.com/2016/05/02/health/biggest-loser-weight-loss.html

Naturevs.nurture

Sexualorientation

•  Influencedbygenesandenvironment– whomyoulove.com(MarcBreedlove,MSU)

•  Concordancerateofacharacteristic:– Theprobabilitythatonememberofatwinpairhasthecharacteristic,giventhattheotherdoes

•  Identicalvs.fraternaltwins:– 100%vs.50%sharedgeneticmaterial

Sexualorientation

•  Concordanceratesforbeinggay:– Maleidenticaltwins:52%– Malefraternaltwins:22%

•  Evidenceforgeneticinfluence:–  Identical>fraternal

•  Evidenceforenvironmentalinfluence:–  Identical<100%

Theolderbrothereffect

•  Themoreolderbrothersamalehas,themorelikelyheistobegay

•  Onepossiblemechanism:– Chromosomes:GirlsareXX,boysareXY– Mom’sbodyviewsnewproteinsontheYchromosomeasinvaders•  Generatesantibodiesthataffectlatermalefetuses•  Somehowmakingthemmorelikelytobegay