DevelopmentalBiologyasaScienceofDependentCo-origination

ScottF.GilbertDepartmentofBiologySwarthmoreCollege

Swarthmore,PA19081USA

Between fertilization and birth, the developing organism is known as an embryo,

and forming an embryo is the hardest thing you will ever do. To become an embryo, you

had to build yourself from a single cell. You had to respire before you had lungs, digest

before you had a gut, build bones when you were pulpy, and form orderly arrays of

neurons before you knew how to think. One of the critical differences between you and a

machine is that a machine is never required to function until after it is built. Every

multicellular organism has to function even as it builds itself.

Developmentalbiologistsarethoseprivilegedtostudytheoriginsand

developmentoftheembryo.Wegettoasksomeofthemostimportantquestions

aboutlife.Howdoesnewnesscomeintotheworld?Howdoesonecell--the

fertilizedegg--dividetobecomethetrillionsofsmallcellsthatcomprisemybody?

Howdoesthisonefertilizedeggcellgenerateallthedifferenttypesofcells—blood

cells,braincells,livercells?Howdothesecellsbecomeorganizedintofunctional

organs?HowisitthatIhaveonlytwoeyes,andtheyarebothinmyhead?WhydoI

haveonlyoneheart?Howdotheorgansknowtheircorrectsize?Howdoorganisms

makecellsthatcanreproduce?Didotherorganismshelpmecomeintobeing?Isthe

formoftheadultsomehowpresentintheeggordoesformarisefromnothing?

ThesequestionshavebeenexplorednotonlybyTsongkhapaandmanyother

BuddhistscholarsfromtheviewpointBuddhistlogicbutalsobymyriadsof

developmentalbiologistsspanningseveralcenturiesusingscientifictechnologies

andtheempiricalmethod.

Asadevelopmentalbiologist,Igettotellanimalstories,modernjatakatalesthat

notonlyillustratethemysteryofdevelopmentbutalsohavethepotentialtohelp

listenersunderstandtheprocessesthroughwhichformarises.Here,Iwishto

deliverthreescientificstoriesaboutanimalcellsandabouttheoriginofanimal

bodypatterns.Thefirstwillbeastoryofearlydevelopment.Indeed,itisapiece

fromtheepictaleoffertilization.Thesecondwillbefromthemiddlepartof

development,whenorgansareforming.Itwillbethestoryofthecoming-into-being

oftheeyes.Andthethirdstorywillbefromalaterstageofdevelopment,soonafter

weareborn.Itwillbeastoryofbloodvesselformation.

Iwillfirstprovidethestories.Afterward,Iwillprovidesomeofthescientific

databehindthesestories.Andasathirdpart,Iwillsuggestthatthesestoriesare

relevanttothinkingoftheworldintermsof(1)flux,(2)context,and(3)the

continuousinterdependent-coming-into-being.

Part1.THREESMALLSTORIES

A.Thestoryofcellularconsummation

Thehumanbodyiscomposedoftrillionsofcellsthatareconstantlybeingborn

anddying.Whatwecall“life’isactuallyasmuchaboutdeath.Throughoutlife,many

trillionsofcellscomeandgo,yetthereistheillusionofstasis.Therearebloodcells,

braincells,stomachcells,andmanyothers.Butonetypeofcellisveryspecial.

Thesearethegermcells.Whileintheembryo,thegermcellswillmigrateintothe

developingtestes,iftheembryoismale.Andtheywillbecomethespermcellsofthe

adult.Iftheembryoisfemale,thegermcellsmigrateintothedevelopingovary,and

theywillbecometheeggsofthematureadult.

Thespermcellsandeggcellsareremarkableinmanyways.Theyhaveonlyhalf

thegenesofnormalcells.Sowhenspermandeggunite,theymakecompletethe

normalnumberofgenes,andthesegenesprovidemostoftheinstructionsfor

normaldevelopment.Thespermandtheeggaretwocellsatthevergeofdeath.

Boththespermandtheeggwillsoonperish.Yet,bytheirinteractions,theycan

makeanorganismthatwilllivesseveraldecades.Bothspermandeggare

remarkablepartners.Outofthemillionsofspermejaculated,onlyaboutadozen

makethefulljourneyandreachthevicinityoftheegg.Andoutofthemillionsof

eggsoriginallyintheovary,onlyabout500willbeovulated,onepermonth;and

onlytheyhaveachanceofmeetingasperm.

Forthesperm,theraceisnotnecessarilytothequickest.Thespermthat

fertilizestheeggisoneofthespermthatcooperatesbestwiththewoman.Forthe

woman’sreproductivetractisnotapassivetubethroughwhichspermrace,andthe

spermthatareejaculatedarenotmaturesperm.Infact,theycannotfertilizeeggs.

Rather,thespermthatgetejaculatedareimmaturesperm.Theyhavetocomplete

theirformation.Andthisisaccomplishedbyinteractingwiththeoviductcellsofthe

woman’sreproductivetract.Thefastestsperm,thosegettingimmediatelytothe

egg,cannotfertilizeit.That’sbecauseitremainedimmature.Thewomen’soviduct

cellschangeandmaturethesperm,givingitthecapacitytofindandfertilizetheegg.

Moleculesintheseoviductcellsbindtothesperm,slowitdown,andchangethe

spermcell’smembrane.Afterthemembranehaschanged,thespermcanthenbind

sperm-activatingsubstancesproducedbythenewlyreleasedegg,andthisbinding

makesspermswimfaster,andgivesthespermdirectiontopropelittowardtheegg.

Onlyafterinteractingwiththeoviductcellscanthespermfindtheeggandfusewith

it.

Andwhenthespermmeetstheegg,itdoesnotboreintoit.Itdoesnotdrillinto

it;itdoesnotpunchaholeinit.Rather,thespermheadleansagainsttheegg,and

theeggsendsoutprocessestoenvelopit.Thespermandeggmembranesfuse,

causingthetwocellstobecomeone.

Andnowthespermreciprocates.Intheoviduct,thespermwasmaturedand

activatedbytheegg.Now,thespermactivatesandmaturestheegg.Forthehuman

eggisalsoimmature.Ithasnotcompleteditsfinaldivision.Thiscompletionofegg

developmenthappenswhenthespermenters.Now,theactivationoftheeggallows

developmenttobegin.

Sowehaveaparableoftwoimmaturecells,bothatthevergeofdeath.Thesperm

getsmaturedandactivatedinthewoman’sreproductivetract,allowingittomature

andactivatetheeggtobegindevelopment.Thisishowourlifebegins.Notin

combat,notinviolence,butinreciprocalinteractingandpartnership.

B.Thestoryoftheeye

Imaginetheheadofanearlyhumanembryo.Intheearlyembryo,thereareno

eyes,ears,nose,tongue;nosound,smell,taste,norealmofseeing--astartingpoint

thatisfundamentallysimilartothatdescribedintheopeningportionof“TheHeart

Sutra.”Theheadisinitiallycoveredwithskin.Therearenotyetholesforthemouth

ornose.Therearenoeyes.Ifleftalone,noeyelenseswillform.Butsomethinghas

totellsomeoftheskincellstobecomethelensesofthetwoeyes.Whatdoesthis?It

isthebrain.Inaspecificregionofthedevelopingbrain,apairofbulgesappears.

Theytraveloutfromthebrain,andtheyeventuallytouchtheskin.Whenthese

youngbraincellstouchtheembryonicskin,theyproducechemicalsthatinstruct

theseskincellstoturnawayfromthepathofskindevelopmentandtoenterthe

pathoflensdevelopment.Thebraintellstheseskincells:“Youaretobecomethe

lensoftheeye.”Andasthelenscellsform,thedevelopinglenscellstellthebrain

cellsthatformedthem:“Andyouarenotgoingtobecomebrain.Youwillbecome

theretinaofeacheye.”Thedevelopinglensisinconversationwiththedeveloping

retina.Theyhelpformeachother.Withoutthelens,thereisnoretina.Withoutthe

retina,thereisnolens.Eventually,theretinawillsecreteafluidthatfillsthe

chamberoftheeye,separatingthetwo.Wherethelensandretinaremainincontact,

theirismusclesformfromtheretina,therebyallowingthelenstofocuslightonto

theretina.Thestalkconnectingtheretinatothebrainbecomestheopticnerve.

Thisishowhumanorgansform.Theydonotcomeintoexistenceindependently.

Theycomeintoexistencethroughtheeffortofacommunityofotherorgans.The

cellsthatbecometheheartneedtheheadandthegutinordertoformproperly.The

cellsthatbecomethebonesofthehandneedsignalsfromtheskininordertogrow.

OneoftheproteinsneededforeyedevelopmentisBMP4.BMP4isachemical

thatgoesfromonecelltoanothercell.Butwhatitdoesisverydifferentindifferent

partsofthebody.Inthehead,BMP4isoneoftheproteinsmadebythebraincells

thatinstructtheskincellstostartbecominglenscells.ButBMP4intheconnective

tissueofthebodysays,“buildbones.”BMP4intheveryearlyembryosays,“Become

skin”.AndBMP4betweenthebonesofourfingerstellsthecellstodie,thereby

separatingourdigits.Contextiseverything.ThereisnoessencetoBMP4.Itdoes

differentthingsindifferentsituations.

Soasorgansform,thereciprocitythatwesawinthespermandeggcontinues.One

seesinterdependentco-origination.Theretinadoesn’tformwithoutthelens

forming.Thelensdoesn’tformwithouttheretinaforming.Onealsoseesthatthe

contextinwhichamoleculefunctionsdeterminesthefunctionofthatmolecule.We

alsoseetheeyeasanorganinflux.Itwasmadebyimmaturecells.Thefunctionof

theadultretinaistoreceivelight.Thefunctionoftheembryonicretinaistoinduce

theformationofthelens.

C.Thestoryoftheintestinalcapillaries

Ourgutcontainstrillionsofbacterialcells.Theyarenotdangerous.Quitethe

opposite,weneedthem,andtheyneedus.Weacquirethesebacteriaatbirth--the

momentwestartcomingthroughthebirthcanal.Ourmotherhasbacteria

throughoutherreproductivetractandgut,andaswepassthroughthebirthcanal,

thesebacteriacolonizeourbodies.Thefirstthingourbodiesdo,beforeeventhe

firstbreathistaken,istoacquirethesebacteria.

Andthisisgood.Onecanexperimentallybreedmicethatlacksuchbacteria.

Thesemicearenotnormal.First,theyhaveanimmunedeficiencyandcannotmake

thenormalamountofantibodies.Second,theylackthenecessarybloodvesselsto

takefoodfromthegut.Third,theyhavebehavioralproblems.Normalmiceand

normalpeoplearefullofbacteria.Andthesebacteriahelpconstructourbodies.

Bacteriaactjustasembryoniccellsdo.Justasthebraincellsputforthchemicals

thatchangegeneexpressionintheskincellstoturnthemintolenses—sothe

bacteriaalsoproducethechemicalsthatactivatecertaingenesinthesurrounding

tissues,andthisgeneexpressiontellsthecellswhattodo.Bacteriaactivatecertain

genesinourguttissues,andtheysuppresstheexpressionofothersgenes.These

changesingeneexpressionthatarecausedbythebacteriaareneededtomake

certainorgans.Wearetoldhowtodevelopnotonlybythecellsweacquirefromthe

unionofspermandegg.Wealsoaretoldhowtodevelopfromover100speciesof

bacteriathatinhabitouryoungbody.Weexpectthebacteria,andwearebornwith

poorlyformedorgansifthesebacteriaarenotpresent.

Forinstance,thesymbioticbacteriainthegut,especiallyagenuscalled

Bacteroides,actuallytellstheintestinecellstoturnonthegenesthatmakeaprotein

calledangiogenin-4.Theintestinalcellsmakeangiogenin-4andsecreteittotheir

neighboringcells.Thecellsaroundtheintestinebindangiogenin-4,andangiogenin-

4tellsthesenearbycellstomakecapillaries.

Butangiogenin-4doesmorethanhelpproducecapillaries.ItalsokillsListeria,a

bacteriathatisacompetitorforBacteroides.Bacteroideshelpsus;wehelp

Bacteroides.

Soimportantarethesesymbioticbacteriathatwehaveintegratedthemintoour

physiology.Duringthelastmonthsofpregnancy,thewoman’shormoneschangethe

typesofbacterialivinginsideher.Thesebacteriaactuallyhelpthepregnantwoman

maintainthefetus.Whenthebabyisborn,itacquiresthesemicrobesasthefetus

passesthroughthebirthcanal.Equallyamazing,whenthemotherfeedsthebaby,

sheisgivingthebabytwosetsofnutrients.Onetypeoffoodfeedsthebaby.The

othertypeoffoodfeedsthegoodbacteria.Thefoodfromthemothercontains

sugarsthatthathumanscan’tdigest.However,theyselectivelypermitthegrowthof

certainbacteria—theoneswewantinthebaby’sbody.Wenourishthesin-boos,

andtheyhelpconstructus.

Suchinteractionsbetweenspeciesiscalledsymbiosis,andwefindthatsymbiosis

isnottheexceptiontotherule.Rather,symbiosisistherule.Oneseessymbiosis

insideourcells,oneseessymbiosisinmakingorgans.Oneseessymbiosisinthe

productionofoxygenandinthenitrogenofoursoil.Weseeitintidegrass

communitiesandinourbodies.Wearenotindividualbodies.Thatisanillusion.We

areecosystemsofco-dependentprocesses.

Sowedonotdeveloponourown.Thefertilizedeggdoesnothavewithinitall

thematerialneededforthecompletionofdevelopment.Weliterally“becomewith

others.”Thisisoneofthegreatbiologicaldiscoveriesofthe21stcentury,andone

thatoverturnsmuchofthecompetitiveparadigmsofthe19thand20thcentury.We

needtheotherspeciestosurvive.That’snotmetaphor.Itisrealityasscienceknows

it.

PartII.ScientificExplication

InthissectionIwouldliketoprovidesomeofthescientificdetailsthatallow

ustotellsuchstories1.

A. FERTILIZATION.Theessenceoffertilizationisthemutualactivationofthespermandeggsuchthatdevelopmentcanbeactivatedinthe

eggandthattheinheritedmaterialcanbetransmittedfromone

generationtothenext.Fertilizationisabouttheinteractionofcells

totransformeachother.

Fertilizationisthestoryofinteractionbetweentwocells,thespermfromthe

male,theeggfromthefemale.Boththespermandeggareimmaturecellsandhave

tobeactivated.Andthisisdonebyactivatingcertainproteinswithinthespermand

egg.

1. Activationofthesperm:I.Capacitation.Theactivationofthemammalianspermisdoneintwosteps,thecapacitationreactionandtheacrosome

reaction.Bothstepsalterthemembraneofspermcellstomaketheirnext

stepspossible.Capacitationallowsthespermtofindtheegg.Theacrosome

reactionallowsthespermtobindtoandentertheegg.Duringcapacitation,

thecellsofthefemale’soviductsbindtothespermandstopthespermfrom

moving.Thiscessationofmovementallowscholesteroltoberemovedfrom

thespermcellmembrane.Thisremovalofcholesterolallowscalciumions

fromthewoman’sreproductivetracttoflowintothesperm,andthese

calciumionsactivatetheadenylatecyclaseenzymeonthespermcell

membrane.Thisenzymeisaproteinthatturnsasmallmolecule,AMP,into

anothersmallmoleculecalledcyclicAMP.CyclicAMPactivatestyrosine

kinaseproteins,andtheseproteinsaddphosphategroupsontootherproteins.

Thesechangescausethespermmembraneproteinstoreorientonthesperm.

1AllthedetailscanbefoundinGilbertandBarresi(2016).ThenotionthatdescriptionsofdevelopmentmightbenefitfromBuddhistphilosophyisnotnecessarilynew(Rose1997,p.34;Barash2013).

Asaresultofcapacitation,theIzumoprotein,whichisnecessaryforsperm-

eggbinding,migratesintothemembrane,whereitwillbefunctionalinbiding

totheegg.Theproteinsthatareneededtoreceivethedirectionalsignalsfrom

theeggarealsoactivated.Capacitatedspermcannowrecognizethese

chemicalsignalsandswimquicklytotheegg.Theuncapacitatedsperm

cannot.

2. Activationofthesperm.II.Theacrosomereaction.Onceneartheegg,themembraneformedduringcapacitationisexchangedforanothercell

membrane,comingfrominsidethesperm.Thischangeiscalledtheacrosome

reaction.Asthespermapproachtheegg,substancesfromtheeggorfromthe

cellssurroundingtheegg(the“cumulus”ofcellsthathadbeenconnectedtoit

intheovary)causethetipofthespermcellmembranetodisintegrate,while

anothermembraneisputinitsplace.Thisnewmembranecontainsthe

proteins(suchasIzumo)thatwillbindtotheegg.Thisnewmembranealso

hastheproteinsthatbindtooutersurfaceoftheegg.Afterundergoing

capacitationandacrosomereactions,thespermiscompetenttofertilizethe

egg.

3. Sperm-eggbinding.I.Zonapellucida.Thebindingofspermandeggalsooccursintwosteps.First,thespermbindstotheprotectivelayeroftheegg,

thezonapellucida.Inhumans,thislayerismadeof4proteins,andithastwo

functions.First,itonlybindsactivesperm.Second,thisproteinshellservesa

protectivefunctionfortheembryodevelopinginsideit,preventingthe

embryofromadheringtotheoviductcellsasittravelstoandintotheuterus.

(Onceinsidetheuterus,theembryodigeststhezonapellucidaandisableto

adheretoandenterintotheuterus.)Theproteinsonthespermbindto

proteins,mainlyproteinZP2,onthisprotectiveouterlayeroftheegg.

Chemicalsreleasedbythespermcanthendigestasmallchannelinthezona

pellucida,allowingthespermtoreachtheegg.

4. Sperm-eggbinding.II.Membranefusion.Whenthespermreachtheegg,theydonotboreintoitordrillintoit.Rather,thespermheadplacesitself

adjacenttothehugeeggsurface,andtheeggcellmembraneextendsfoldsthat

envelopthesperm.TheIzumoproteinonthespermmembranerecognizesa

receptor,Juno,ontheeggmembrane.Ifonewantstousemetaphors,theegg

embracesthesperm.Andthen,thespermcellmembranemeltsintotheegg

cellmembrane,andspermandeggbecomeone.

5. Eggactivation.I.Re-initiatingcelldivisionanddevelopment.Thespermcannowreciprocateandactivatetheegg.Aproteinfromthesperm—PLC-

zeta—releasescalciumionsfromtheirstoragevesiclesinsidetheegg.Thisis

verysimilartotheuseofcalciumionsduringthecapacitationandacrosome

reactionsinthesperm.Thecalciumionsactivatecertaineggproteinsthat

activateothereggproteins.Again,thisisverymuchlikewhathappensin

capacitation.Theactivatedeggproteinsdoseveralthings.First,theychange

theeggcellmembranesuchthatitcannotbindanymoresperm.Onlyone

spermispermittedtoentertheegg.Second,theactivatedproteinsre-startthe

maturationoftheegg.Thehumaneggisstoppedinthemiddleofitssecond

meioticdivision.Itisstillimmature.Theentryofthespermallowstheeggto

matureandcompleteitssecondmeioticdivisiontogiveithalfthenumberof

genes.Andthird,thenewlyactivatedenzymesre-starttheproductionofnew

proteins,theproteinsthatwillallowcelldivisiontotakeplace.

6. Eggactivation.II.Theunionofgeneticmaterials.Fertilizationhastwofunctions—theinitiationofdevelopmentandthecreationofanewgenome

whosegenesarederivedhalffromthemotherandhalffromthefather.After

thespermhasactivatedthelastcelldivisionoftheegg,theeggnowhasa

nucleuswithhalfthenumberofgenes,andthespermnucleusalsohashalfthe

numberofgenes.Howdothesetwonucleifindeachother?Thisfeatinvolves

anotherstepofsperm-eggcooperation.Thespermbringsinnotonlya

nucleus,butalsothecentrosome,asetofproteinsthatmakefibers.The

chemicalsthatmakethesefibers,thetubulinproteins,comefromthemother.

Thespermcentrosomespinsitsnetofeggproteins,catchingthefemale

nucleus.Then,themaleandfemalenucleimovetowardeachotherinthisnet,

andfinallycometogetherandfuse.Thechromosomalgenesofthemotherjoin

withthechromosomalgenesofthefatherandcelldivisionoccurs.The

formationofthenewpersonhasbegun.

Thus,thereareenormousamountsofcooperationtakingplaceduring

fertilization.Thefemalereproductivetractandeggarenotalwayspassive.They

matureandactivatethesperm.Onceactivated,thespermbecomescapableof

initiatingthematurationoftheegg.Thespermandtheeggarebothactiveand

passive,andthespermandtheeggactivateeachotherbysimilarchemicalmeans.

(Interestingly,thesemechanismsofactivationusemanyofthesameproteinsthat

willlaterbeusedintransmittingneuralsignals.)Moreover,thespermandtheegg

bringdifferentelementsintothefertilizedegg.First,whilebothspermandegg

bringthesamenumberandtypeofgenes,somegenescanonlybeactiveifthey

comefromtheegg,whileothergenesareonlyactiveiftheycomefromthesperm.

LiketheBuddhistnotionsofredmattermakingsomeorgansandwhitematter

makingotherorgans,thespermandegghavesomecomplementaryfunctionsand

arebothneededtomakeacompletebody.Thespermbringsinthecentrosome,

whichisnecessaryforcelldivision.Themotherbringsallthemitochondria,which

providetheenergyforsuchdivision.Sowhilethespermandeggaretwocellson

thevergeofdeath,iftheycooperatesuccessfully,thehumanembryobeginstoform.

B. ORGANFORMATION.Theessenceoforganformationistheexpressionofdifferentgenesinthecellsofdifferentorgans.

Vertebrateorganformationisabouttheinteractionoftissuesto

mutuallytransformeachother.

Fertilizationgiveseachofusourgenome—thesetofgeneticinstructionsthatare

criticalinconstructingandmaintainingourbodies.Asthefertilizedeggdividesto

producealldifferentthecelltypesofthebody,thegenesineachcellreplicateasthe

celldivides,sothateverycellhasthesamenumberandtypesofgenes.Cloninghas

shownthatthegenesofeachcellarethesame.Thegenesaretheinstructionsthat

makeproteins,andtheproteinsdotheworkofthecell.Buteachgeneisnotactive

ineverycell.Quitethecontrary;differentgenesareactiveindifferenttypesofcells,

andtheproteinsmadebythesedifferentgenesarewhatgivetheorganstheir

differentfunctions.Intheredbloodcells,thegenesforhemoglobinareactive,and

thisredcompoundtransportsoxygentothecells.Thepancreaticbetacellsdonot

makehemoglobin.Rathertheyactivatethegenesthatmake,amongotherthings,

insulin,theproteinneededforsugarmetabolism.Thelensesofoureyesaretoldto

activatethegenesthatmakethetransparentcrystallineproteins,whilethegenesin

theepidermisofourskinaretoldtomakesspecialkeratinproteinsthatthatare

water-resistantandelastic.

Sothegenomehastobetoldwhichgenestoactivateinwhichcells.Howisthis

done?Theagentsofdifferentialgeneexpressionareasetofproteinscalled

transcriptionfactors.Theseproteinsbindtoacertainregionofthegeneandallow

thebindingofanenzyme,RNApolymeraseII,whichstartstheprocessesbywhich

thegenebecomesactiveandmakesproteins.Differenttranscriptionfactorsbindto

differentgenes,andthecombinationofcertaintranscriptionfactorsallowthegenes

tobecomeactive.

Whichtranscriptionfactorsactinacelldependsonwherethecellisandwhat

thatcell’sneighborsare.Contextiscritical.Wearethinkingwithcellsthatcould

havebeenusedforeating,hadtheybeeninadifferentpartoftheembryo.Asthe

fertilizedeggdividestobecomeaballofcells,differenttranscriptionfactorsare

activatedintheinsidecellsthantheoutercells.Thisisthefirstdistinctioninthe

embryo.Theoutercellswillbecometheplacenta;theinnercellswillbecomethe

body.Thesetissues,nowdifferent,influenceeachothertobecomemoretissues

(Stephensonetal2012;Harrisonetal2017).

Oneofthebestexamplesoforganformationisthatoftheeye.Theformationof

theeyebeginswhentwoareasofthedevelopingforebrainbrain,eachexpressing

theRxtranscriptionfactor,areinstructed(bytheproteinsactivatedbythis

transcriptionfactor)togrowtowardtheskin.Whenthesebraincellsreachtheskin,

theyflattenagainstitandsecreteagroupofproteinsincludingBMP4,Fgf8,and

Notch.Eachoftheseproteinsbindstoaspecificreceptorproteinonthesurfaceof

theembryonicskincells.Whentheyareboundtothereceptorproteinsonthe

membranesoftheneighboringskincells,thereceptorsactivatecertain

transcriptionfactorsthattelltheembryonicskincellstoelongateandtobecomethe

transparentcellsofthelens.Thesecellsstartmakingthecrystallineproteinsthat

characterizethelenscells.Oneofthetranscriptionfactorsinducedinthedeveloping

lenscellsactivatesthegeneforanotherproteinthatissecretedfromtheelongating

lenscell.Thisproteinbindstoreceptorsonthebraincellsandtellsthebraincellsto

becometheneuralretinacells.Asthebraincellsaretellingtheskincellstobecome

lenses,theskincellsreciprocatebytellingthoseparticularbraincellstobecomethe

retina.

Inaddition,thephysicaladhesionofthedevelopinglenscellsandthedeveloping

retinalcellspreventsothercellsfrommigratingintothisarea.Themigratingcells

wouldhavebeentheneuralcrestcellsthatformthedermisoftheheadskin.The

neuralcrestcellsalsohavetheabilitytoblockthesignalsmadebythedeveloping

lensandbrain.Sotheseantagonisticcells,whichwouldhavepreventedlens

formation,arephysicallyblockedfromenteringtheeye-formingareas.

TheFGF8,BMP4,andNotchsignalsactivatetranscriptionfactorstoactivateor

repressparticulargenes.Pax6,Sox2,andL-MAFaretranscriptionfactorsthatare

neededtoactivatemanyofthecrystallinegeneofthelenses.Pax6isintheentire

headectoderm,anditisplacedtherebyearlierinductionsinvolvingtheheartand

gutcells.Sox2isactivatedinthelensbyBMP4fromthebraintissue,andL-Mafis

similarlyactivatedbyFgf8.Pax6,Sox2,andL-Mafbindclosetoeachotheronthe

DNAofcertaingenes,suchasthecrystallinegenes.Andbytheirinteractions,RNA

polymeraseisallowedtobindtothem,andthecrystallinegeneisactivated.Usually,

itisacombinationoftranscriptionfactorsthatactivatesgenes.Andthese

transcriptionfactorsareactivatedbysignalingchemicalsoriginatinginthe

neighbors.Theruleoforganformationisthatneighborsbuildneighbors.

Againoneseesthisco-dependenceofembryonicdevelopment.Thegenesare

bothactiveandactedupon;thecellsarebothactedandactedupon.Eachgroupof

cellshelpsdeterminethefateoftheother.

C. Theessenceofdevelopmentalsymbiosisisthatcertainmicroorganismssignalnormaldevelopmentinthehostorganism.

Thistypeofdevelopmentinvolvestheinteractionsbetweencellsof

differentbiologicalspecies.

Wewereneverindividuals2.Wearenotindividualsanatomically,asatleast50%of

thecellsinourbodyaremicrobes.Wearenotindividualsphysiologically,as30%of

thesolublematerialinourbloodisderivedfromthesebacteria.Ourmetabolismis

intimatelylinkedtotheirs.Wearenotindividualsbydevelopmentalcriteria,since2DetailsofthesestudiescanbefoundinGilbertetal(2012),McFall-Ngaietal2013).

bacteriaarenecessaryforournormaldevelopment.Infact,noneofusareindividual

animals.Foroveradecadenow,severalbiologistshavebeenconsideringanimalsas

holobionts—theorganismplusitscoloniesofpersistentmicrobialsymbionts.When

youthinkofacow,youmaythinkofaslowmovinganimalthateatsgrass.Only,it

can’teatgrass.Thegenesofthecowencodenoproteinsthatallowhertodigest

celluloseoranyofthewoodypartsofgrass.Thoseproteinsaremadebythe

bacterialsymbiontsofitsstomach.Thecowisnotacowwithoutthese

microorganisms.Similarly,termitescan’teatwood.Thatabilityisgiventothemby

theirmicrobes.

Themicrobesactivatenormalgeneexpressionjustlikeanembryonictissue

would.Thevertebrategutwithoutitssymbiontshasadifferentpatternofgene

expressionandislikeageneticmutant.Infish,thedivisionofthegutstemcellsis

inducedbythegutbacteria,andwithoutthebacteriacertaincellsdon’tform.Iwish

togivetwofascinatingexamplesoftheneedformicrobialinvolvementinnormal

development.

First,thebobtailsquidfeedsintheshallowwatersofftheHawaiianislands.

However,itisonlyabigasyourpalm,andmanyothercreaturesfindittasty.When

itfeedsduringthefullmoon,thelightofthemooncancastthesquid’sshadowon

theseafloor,showingittoitspredator.Toavoidthishappening,thesquidhas

evolvedanamazingstructure—thelightorgan.Onthebellyofthesquid,thereisa

pouchthatglowssoftlyandcancancelitsshadow.Thisiscalledthelightorganof

thesquid.However,itisnotthereatbirth.Itismadebyasinglespeciesofbacteria,

Vibriofischeri.Thesquidcollectsthesebacteriainsuchahighquantitythatthey

startglowing,somethingtheydonotdoontheirown.Sothelightorganisapieceof

anatomythatismadeinoneorganismbyanotherorganismforthebenefitofboth.

Thesquid’sdevelopmentisnotcompletewithoutthemicrobe;andthemicrobe’s

developmentisalsochangedbyitsbeinginsidethisorgan,whichprovidesitasafe

home.

Butletmenowtalkofsomesciencethatwouldborderonscience-fiction

werenotthepropercontrolsdone.Onelargestudy(Hsaioetal2013)usedviral

stressinmotherstoinduceanautism-likeconditionintheiroffspring.These

“autistic”micespendalotoftimeself-grooming,lacknormalexploratorybehaviors,

andprefersolitarycages.Thisstudyfoundthattheautistic-likemiceactmorelike

normalmicewhenyoualtertheirbacteria.Ifoneaddscertainspeciesof

Bacteroides,thisaltersthecommunityofthebacterialsymbionts,anditincreases

theintegrityofthegutepithelium.Thissimpleprocedurestopstheleakingof

bacterialproductsintothegutandnormalizesseveraloftheautism-likebehavioral

abnormalities.Oneofthesechemicals,4EPS,ismadebybacteriaandcauses

anxiety-likesymptomsinmice.Inthe“autistic”micethisproductisseenin

relativelyhighamountsinthecirculation.Inthenormal(bacteria-containing)mice

withoutthesesymptoms—andinthe“autistic”micethatweretreatedwiththe

bacteria—4EPScanhardlybedetected.Thisstudyopensupanewareathat

investigatescognitiveandemotionalsituationsasproductsofbacterialmetabolism

(Hsaioetal2013;Desbonnetetal.2014).Differentmicrobesmaymakeusdifferent

people.Differentmicrobesprovidedifferentamountsofresistancetokwashiorkor

inhumans(Smithetal2013)andmalariainmice.(Villarinoetal2016).

Wearemultilineageorganisms.Theseparationofusfromourenvironmentisan

artificialone,basedonvisualcuesandnotontheevidenceofanatomy,physiology,

ordevelopmentalbiology.Wehavenumerousecosystemswithinus,andweare

partofeachoftheseecosystems(Gilbert2014).

.

III.CODA:Becomingwithothers

Wealwaystellstoriesbylinkingperceptionsintoanarrative,aplotwitha

beginning,middle,andanend.However,scientificstoriesdifferfrommanyother

storiesbecausetheyareseverelyconstrainedbydata3.Theyarealsoseverely

limitedbycontrols,whichmeannotonlythatacertainstoryispossible,butalso

thatotherstoresarenotpossible.

Forthepastcentury,therehavebeenthreemajorbiologicalstoriesthathave

failedthetestofdata.Thefirsthasbeenhasbeenthatthestorythatfertilizationis

allaboutmalestrugglesandsuccess.Theeggwasapassiverecipientofthesperm,

andthefemalereproductivetractapassiveconduit.Thatstoryiswrong.

Fertilizationisastoryaboutinteractionandcooperation.Ifthereiscompetition,itis

usuallyintheformofwhichspermcellcooperatesbest.

Second,wewereoftentoldastorythatthecreationofanembryoisstrictly

controlledbyourgenes.Thegeneswereconsideredtobeouressence;theyarewho

weare.ThenotionthatourDNAisseenasthebasisforourautonomousself-hood

hasbeendocumentedbyhistoriansandsociologistswhostudiedtherhetoricof

DNAinWesternsociety(forinstance,NelkinandLindee1985).InWestern

countries,anti-abortionwebsitesmaintainthatweareexactlywhoweareat

fertilization;evenautomobileadsuseDNAasmetaphorforessence(Gilbertand

Howes-Mischel,2004).

Thisstoryhasfallenapart.Wenowknowthattheenvironmentplayscriticalroles,

andthattheenvironmentcanalsochangegeneexpression.Wealsoknowthat

development(luskyichagstshul;howthebodyismade)consistsofthemakingof

partsthatbecomedifferent,andthatoncedifferent,thesepartsinteractwithone

3Garrett(2008)hasclaimedthatthestoriestoldaboutembryologyintheTibetanBuddhisttraditionarenotscientificstories,astheyarestoriesnotabouttheembryobutabouttheadept(P.57,157).ExotericBuddhiststoriesareaboutgestationbeingarealmofsuffering;exotericBuddhiststoriesconcerntheadept’sbeingrebornintoanenlightenedbody.Garrett(p.130)claimsthatthe12stepsofdependentself-originationcreatesamiddlegroundbetweentheextremesofeternalism(thatthereisaneternalessenceofeachperson)andnihilism(thatthepersonisdestroyedatdeath).

anothertoformorgans4.Embryonicdevelopmentisbasedonspecificinduction,

suchastheformationofthelensbybraintissuetouchingtheskin.Noothertissue

butthebrainwillturnskinintolens.Noothertissuebutthedevelopinglenswill

turnbrainintoretina.Developmentalbiologyisasciencebasedonthenotionof

“specificconditionality,idaṃpratyayatā,”namely,thatonepartcomesintobeingby

interactingwithanotherpart.“Thisisbecausethatis.Thisisnotbecausethatis

not.”However,thethirdpostulateofspecificconditionality--asthisceasestobe,so

doesthat—isoftencircumventedbytheembryo.WhencellAtellscellBtobecome

B’,theproductofthegenesthatareactivatedinBtoeffectthisconversionoften

activatethemselves.ThecellbecomesB’evenaftercellAdiesormovestoanew

location.Iftheteacherdiesormoves,theteachingisstillcontinued.

Wearenotmerelyself-manifestations,the“readouts,”ofourgenes.“Self-

manifestation,”asthethirdKarmapa,HisHolinessRangjungDorje(1284-1339),

explainedinhisWishingPrayerfortheAttainmentoftheUltimateMahamundra,“has

neverexistedassuch,andiserroneouslyseenasanobject.”Indeed,accordingtothe

Buddhisttradition(asintheMahamudra),attachmenttothisnon-existentself-

manifestationisarootoftheperniciousdualityof“Iandother.”However,rather

thanourbodyhavingagenome-defined“essence,”weareconstructedbypartsthat

receivetheiridentityastheyarebeingconstructed.Thisrelatesdirectlytothe

principleofPratityasamutpada,whichemphasizesthatwhatappearstobean

individualentitycomesintoexistencethoughinterdependentrelationshipsthat

createoneanother,inaprocessofcontinualarisingandceasing.

4Developmentfindsitselfastheintegratorbetweenstructuralbiology(anatomyandphysiology)andevolution.Oneachievesevolutionarychangesbyalteringthepatternsofdevelopment.Thisisthescienceofevolutionarydevelopmentalbiology.Oneofthefundamentalprinciplesofevolutionarydevelopmentalbiologyisthatofthe“smalltoolbox.”Fromusingthesametoolsindifferentcontexts,onecangeneratethediversityoforganisms.InBuddhistphilosophy,thisistheproblemofhomologouscauseandeffect(rgu‘brasbudangrjessumthunpa).AccordingtoGarrett(2008),bothKyempaTsewangandLodröGyelpoaskedhowaninfinitevarietyofformscanbegeneratedfromasmallsetofcauses.Thisisacentralquestionofevolutionarydevelopmentalbiology.

Indeed,notonlyisinteractioniscritical,butsoisimpermanence.Impermanence

isseeninthetransientorgansoftheembryo,whichexisttomakeotherorgansbut

thenperishthemselves.Theprimitivestreakandnotochordarecriticalinforming

theembryo;buttheyarenotorgansofthenewborn.Impermanenceisalsoseenin

thefundamentalmetabolismofthecells.Weretainouridentitysolelybychanging

ourcomponentparts,asweeat,drink,andexcrete.Theworldpassesthroughusas

wepassthroughtheworld(Jonas1966;Gilbert1982).

Andindevelopmentalbiology,contextisalsocritical.BMP4isimportantin

makingthelensoftheeye.Butinanothercontext,thehand,BMP4tellsthecells

betweenourfingerstodie.Inanothercontext,theearlyembryo,ittellscellsto

becometheskinandnotthenervoussystem.Inanothercontext,itinstructscellsto

becomebone,andinadifferentcontext,itinstructscellstobecomeheart.Sowhat

thismoleculedoesdependsonwhereandwhenitisexpressed.Specifically,the

functionofthemoleculedependsuponthehistoryofthecellreceivingit.Thesame

pathwaysusedforactivatinganeggwillbeusedforneuraltransmission.

Andthethirdstoryofthe20thcenturythatdoesn’tstandthescientificscrutinyof

the21stcenturyisthatweareunilineageorganismswhosegenomesarein

competition.Inthatperspective,lifeisseenasacontinuousstruggleofeachagainst

all.However,anewstoryisemerging—thateachorganismisacollectionofspecies,

aholobiont,andthatmostevolutionoccursthoughinterspeciescooperationrather

thanintraspeciescompetition.AsMargulisandSaganwrote(1986),“Inshort,I

believethatmostevolutionarynoveltyaroseandstillarisesdirectlyfromsymbiosis.

Lifedidnottakeovertheworldbycombat,butbynetworking.”Thisisstilla

controversialstory;butIthinkitwillbeoneofthemostfundamentalchangesinthe

wayWesternscienceviewsnature.Onereviewer(Bolker2016)recentlyreported—

“Theclaimthat‘alldevelopmentisco-development’…soundsalittlenewageinthe

contextofcurrentindividual-basedparadigmsforthinkingaboutdevelopment,butI

suspectthatwithinthenextdecade,wewilltakeourstatusasholobiontsfor

granted.”

Weareseeinglifeas“becomingwiththeother.”Thisisanewscientificstorythat

maymakethecompetitionstoryeitheruntenableasamechanismforchangeora

fine-tuningmechanismthatmayworkwithinaspecies.AsLamaTsongKhapa

noted,one’sviewofnaturechangeswhenonerealizestheco-dependentoriginsof

allparts.“Justseeingthatinterdependenceneverfailsbringsrealizationthat

destroyshowyouholdtoobjects,andthenyouranalysiswithviewiscomplete.”

Onefindscontext,interdependence,andimpermanenceasnormalinanimal

development.Onecanmeditateonanembryoasonecanonamandala.Indeed,in

hisbookontheemergenceoforderindevelopment,JohannesHoltfreter(1968,p.

xi),oneofthemostimportantbiologistsoftheTwentiethCentury,wrote

Wemanagedmoreorlesssuccessfullytokeepourworkundisturbedbyhumanity’sstrifeandstrugglearoundusandproceededtostudytheplantsandanimals,andparticularly,thesecretsofamphibiandevelopment.Here,atleast,intherealmofundespoiledNature,everythingseemedpeacefulandinperfectorder.Itwasfromourgrowingintimacywiththeinnerharmony,themeaningfulness,theintegration,andtheinterdependenceofthestructuresandfunctionsasweobservedthemindumbcreaturesthatwederivedourownphilosophyoflife.Ithasserveduswellinthiscontinuouslytroublesomeworld.

ThismeditationontheembryoreflectsthatofLamaTsongkhapa.ForHoltfreterthe

experienceoftheembryoinstilledfaith,banishednegativity,andstabilizedhis

otherwisechaoticmind.Theinterdependenceofstructuresisnotbeingimposed

fromwithout.Itisbeingdiscoveredandappreciatedbythescientists.Similarly,one

oftheworld’sbestfertilizationresearchers,EdwardE.Just(1939,p.368),wrote

explicitly,

Whetherwestudyatomsorstarsorthatformofmatter,knownasliving,alwaysmustwereckonwithinter-relations.

And in my science textbook on Ecological Developmental Biology, I cite Nagarjuna as

someone who saw interdependent creation as the basis of the world. Developmental

biologists do, as Lama Tsongkhapa (cited in Hixon, 1993) suggested, “listen to the

harmonious symphony of interdependence.”

Embryologyisalwaysrepletewithmoralandpoliticalcategories(BGSG1988;

Martin1991;Garrett2008,p.17).Thestoryofourdevelopmentisanoriginstory,

andsuchstoriesareinstructiveaswellasdescriptive.Sowemustbecarefuland

judgesuchstoriesagainstaculturalframework.Arethesescientificstoriesorare

thesestoriesthatmerelyrepeatonamicroscopiclevelthevaluesthatsocietyis

expectedtogivemenandwomen?Isthescientificnarrativebeingusedtoreinforce

capitalistvalues,democraticvalues,authoritarianvalues,compassionatevalues?

Andifso,isthereanyjustificationtoit?

Thereisastory,notconfirmablebyscience,thatbeforehisbirth,TheBuddha

gavesermonsfromhismother’swomb(Garrett2008,p.102).Perhapsbylookingat

theembryo,though,weareindeedtaughtthatallthingsareimpermanent,that

contextiscritical,andthatourcomingintoexistenceisbasedinterdependent

becomingswithothers.Thisco-dependentorigination,Pratityasamutpada,appears

tobetheruleofnature,whetheritisonthecellularorecologicallevel.Itisprobably

mosteasilyseenindevelopment,whichisabouttheformationofbodies.

Developmentalbiologyisascienceofbecoming,context,andtransience.Ofthe

TwelveLinkedStagesofInterdependentCausation,elevenoccurbeforeorduring

birth(SamyuttaNikaya;Hopkins1983;Garrett2008).

Biologicallyspeaking,wearenotandhaveneverbeenindividuals.As

expressedbyanatman,wearenotapartfromnature.Wemustbecomeusedto

seeinglifeasawebwherechangesinoneprocesscancausechangesinall.AsRev.

MartinLutherKing,Jr,(1963)notedabouthumanrelations,“Wearecaughtinan

inescapablenetworkofmutuality,tiedinasinglegarmentofdestiny.Whatever

affectsonedirectly,affectsallindirectly.”

OrasLamaTsongkhapahaswritten(quotedinThurman2014)p.178:WhateverdependsonconditionsIsemptyofintrinsicrealityWhatexcellentinstructioncouldtherebeMoreamazingthanthisdiscovery?

SoIwillfinishbyshowingsomethingamazing--aphotographtakenby

developmentalbiologistandBuddhistmonkWillliamBates,whowasaninstructor

intheScienceforMonksprogramin2006and2007.

Toabiologist,it’sobviouswhattheseare.Theyarefrogeggsinapond.Butwhen

youseethecontextofthephotograph,onerealizesthatthisisnotapond.Itisan

elephant’sfootprint.Whowouldhavethoughtthatthesefrogshaveanexistence

thatdependsonelephants,andthattheelephanthasbecomepartofthelifecycleof

thetoad?Maybethesearenotmerelyfrogeggs;maybetheyareIndra’spearls.

Acknowledgements:First,Iacknowledgeandthankmyteachers:RandallHuntsberryforintroducingtometothePrajnaparamitatextsanddiscussingwithmetheideasofNagarjuna;andRobertAuerbachandDonnaHarawayfortheirdiscussionsonembryosandco-origination.TheauthoralsowishestothankAnnaEdlundforherimportantcontributionstomakingmyideasaccessible,andtoWilliamBatesandSteveBorishfortheirdiscussionsconcerningthemeaningofBuddhistembryologicaltexts.TheauthoralsowishestoacknowledgeandthankETSIandH.H.TheDaliLamaformakingpossiblethistalk.

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