Pregnant Females as Historical Individuals: An Insight From the Philosophy of Evo-Devo

F on ie s in Psychology | www. on ie sin.o g 1 Janua y 2021 | Volume 11 | A icle 572106
HYPOTHESIS AND THEORY
published: 20 Janua y 2021
doi: 10.3389/ psyg.2020.572106
Edi ed by:
Ma ía Ce ezo,
Uni e si y o Mu cia, Spain
Re iewed by:
And ea Pa a icini,
Uni e si y o Milan, I aly
James DiF isco,
KU Leu en, Belgium
*Co espondence:
A an za E xebe ia
[email p o ec ed]
o cid.o g/0000-0003-2301-0925
†These au ho s ha e con ibu ed
equally o his wo k
Special y sec ion:
This a icle was submi ed o
Theo e ical and Philosophical
Psychology,
a sec ion o he jou nal
F on ie s in Psychology
Recei ed: 12 June 2020
Accep ed: 03 Decembe 2020
Published: 20 Janua y 2021
Ci a ion:
Nuño de la Rosa L, Pa liče M and
E xebe ia A (2021) P egnan
Females as His o ical Indi iduals: An
Insigh F om he Philosophy o
E o-De o.
F on . Psychol. 11:572106.
doi: 10.3389/ psyg.2020.572106
P egnan Females as His o ical
Indi iduals: An Insigh F om he
Philosophy o E o-De o
Lau aNuño delaRosa
1†, MihaelaPa liče
2† and A an zaE xebe ia
3*†
1 Depa men o Logic and Theo e ical Philosophy, Complu ense Uni e si y o Mad id, Ciudad Uni e si a ia, Mad id, Spain,
2 Depa men o Theo e ical Biology, Uni e si y o Vienna, Vienna, Aus ia, 3 Depa men o Logic and Philosophy o Science,
IAS Resea ch Cen e o Li e, Mind, and Socie y, Uni e si y o he Basque Coun y, UPV/EHU, Donos ia-San Sebas ián, Spain
C i icisms o he “con aine ” model o p egnancy pic u ing emale and emb yo as sepa a e
en i ies mul iply in a ious philosophical and scien i ic con ex s du ing he las decades. In
his pape , weexamine how his model unde lies ecei ed iews o p egnancy in e olu iona y
biology, in he cha ac e iza ion o he ansi ion om o ipa i y o i ipa i y in mammals and
in he selec ionis explana ions o p egnancy as an e olu iona y s a egy. In con as , ecen
e o-de o s udies on eu he ian ep oduc ion, including he ole o in lamma ion and new
ma e nal cell ypes, ga he e idence in a o o conside ing p egnancy as an e ol ed
ela ional no el y. Ou hesis is ha om his pe spec i e wecan iden i y he eme gence o
a new his o ical indi idual in e olu ion. In e o-de o, his o ical uni s a e concep ualized as
e ol ed en i ies which ul ill wo main c i e ia, hei con inuous pe sis ence and hei
non-exchangeabili y. As p egnancy can beindi idua ed in his way, wecon end ha p egnan
emales a e his o ical indi iduals. Wea gue ha his o ical indi iduali y di e s om, and
coexis s wi h, o he iews o biological indi iduali y as applied o p egnancy ( he physiological,
he e olu iona y and he ecological one), bu b ings o wa d an impo an new insigh which
migh help dissol e misguided concep ions.
Keywo ds: e o-de o, indi iduali y, p egnancy, ep oduc ion, his o ical kinds, no el y
INTRODUCTION
The indi iduali y o p egnancy cons i u es an in iguing philosophical p oblem conce ning he
kind and numbe o biological indi iduals and he p ocess o indi idua ion in ol ed. Kingma’s
(2018, 2019a) me aphysical wo k has been pi o al o he ecen philosophical ein oduc ion
o he opic o p egnancy. Focusing on pa hood ela ions, Kingma con on s he ecei ed
iew o p egnancy, whe e emales a e concep ualized as “con aine s” o hei o sp ing,1 and
a gues ha emb yos a e ins ead a pa o a la ge whole ha she calls “ he g a ida.”
Ea lie philosophical e lec ions on p egnancy had al eady c i icized he con aine model
as a iew deeply en enched bo h in biomedical ca e and e e yday li e, and emphasized he
impo ance o examining he special na u e o he ela ions be ween emales and emb yos.
Fo ins ance, Young (1990) obse ed ha p egnancy dese es phenomenological a en ion because
i cons i u es a unique way o being an indi idual, one in ol ing an inne ela ion wi h ano he
being, which is pa ly iden ical and pa ly ex aneous o he p egnan subjec . Simila ly, Howes
(2008) elabo a ed on he opic o p egnancy om an immunological pe spec i e, and conside ed
1
Following Blackbu n and S a ck (2015) we use he e m “emb yo” in a b oad sense ( om implan a ion o bi h) ha
also includes e uses.
Nuño de la Rosa e al. P egnan Females as His o ical Indi iduals
F on ie s in Psychology | www. on ie sin.o g 2 Janua y 2021 | Volume 11 | A icle 572106
ha bo h he classical con aine model and he unde s anding
o he emb yo as a pa o “ he mo he ’s lesh” ail o acknowledge
he impo ance o he dynamic ma e ial ela ions be ween
emales and emb yos.
As he a o emen ioned philosophe s sugges , he p e alen
biomedical concep ions o p egnancy, cha ac e ized by a
conside a ion o emale and emb yo as sepa a e biological en i ies,
need o be eexamined. Jus like insec colonies, symbio ic
o ganisms, o he Po uguese Man-O-Wa , p egnancy challenges
in i s own way he commonsense delinea ion o biological en i ies
as dis inc , sel -enclosed, and independen indi iduals. Howe e ,
he p oblem o he indi iduali y o p egnancy has ecei ed sca ce
a en ion wi hin he philosophical communi y discussing biological
indi iduali y (bu see Kingma, 2019b). The pe spec i e weadop
in his a icle pays a en ion o ecen wo k on he e olu ion
o ep oduc ion, in pa icula ele an e olu iona y de elopmen al
biology (e o-de o) on p egnancy, o examine he philosophical
ques ion o he kind and numbe o indi iduals in ol ed.
The ield o e olu ion is ce ainly o e ep esen ed in philosophical
deba es on biological indi iduali y (P adeu, 2016a). Howe e , he
implica ions o e o-de o s udies o he indi idua ion o li ing
en i ies a e o en igno ed. E en hose c i ical o he su iciency
o e olu iona y no ions o indi iduali y s ill end o associa e
e olu ion wi h selec ion. In con as wi h his end, we show
ha ex an no ions o indi iduali y do no ai h ully g asp he
unique biological ea u es o p egnancy as hey a e highligh ed
in ou e olu iona y accoun , and ha new c i e ia o his o ical
indi idua ion used in e o-de o ende signi ican new insigh s
on biological indi iduali y.
The s uc u e o ou a gumen will be as ollows. Fi s ,
we econs uc wo main assump ions unde lying he es ablished
accoun o p egnancy in e olu iona y biology. Then, wep esen
new s udies on he e o-de o o p egnancy ha show ha he
ecei ed unde s anding o ep oduc i e modes as s a egies o
maximizing i ness does no su ice o explain eu he ian
p egnancy, inso a as i ails o conside he ela ional p ope ies
o ep oduc ion and hei ma e ial e olu ion. The eupon,
we elabo a e an al e na i e accoun based on he hypo hesis
ha p egnancy is an e ol ed ela ional no el y ha gi es ise
o a new kind o his o ical indi idual. In he las sec ion,
we discuss how his no ion di e s om, bu may also coexis
wi h, o he concep s o biological indi iduali y.
RECEIVED VIEWS ON THE EVOLUTION
OF PREGNANCY
In his sec ion, wep o ide a concise o e iew o he na a i es
ha unde lie classical iews on p egnancy in e olu iona y
biology.2 These iews ha e long- eaching consequences o
2
Social ep esen a ions o scien i ic knowledge use me apho s in luenced by
social s e eo ypes (see e.g., Wagne e  al., 1995 o he opic o concep ion),
bu also scien i ic accoun s a e in luenced by social, and pa icula ly by gende
biases (see Ma in, 1991, o he same opic). The language used in biological
accoun s o p egnancy is a pa icula ly good illus a ion o how he social
pe cep ion o a biological p ocess has in luenced i s scien i ic in e p e a ion,
and ice e sa.
he concep ualiza ion o he indi iduals in ol ed in p egnancy,
some o which we e iew in his sec ion, ocusing on wo
main h eads, namely: he emphasis on an e olu iona y
con inui y be ween o ipa i y and i ipa i y, and he explana ion
o p egnancy as an e olu iona y s a egy o maximizing
i ness.
Fi s ly, he li e a u e on he e olu ion o p egnancy
emphasizes a o m o e olu iona y con inui y om o ipa i y
o i ipa i y, in which he unc ions o p o ec ing and nou ishing
he emb yo ha a e ul illed by special s uc u es in o ipa ous
animals (e.g., he egg shell and yolk) a e ans e ed o he
physiology o he p egnan emale in i ipa ous animals.
Acco dingly, con inui y is pic u ed as an e olu iona y p ocess
o spa ial in e naliza ion (Rosslenb oich, 2014). In he con ex
o p o isioning, p egnancy is ega ded as a swi ch in pa e ns
o emb yo nu i ion, om e ie ing he nu ien s o
de elopmen om he yolk o ex ac ing hem di ec ly om
he mo he ia he placen a.3
Cen al o his na a i e is he way in which he placen a,
an o gan o emb yonic o igin, has a ac ed eno mous a en ion
in s udies o p egnancy as being he si e o ma e ializa ion
o mo he - e us communica ion.
The easy accessibili y o emb yonal placen al (in con as
o ma e nal u e ine) issue has likely played a majo ole in
biasing he a en ion owa ds his o gan, a he han o he
u e us, as e lec ed by he numbe o scien i ic associa ions
dedica ed o placen al esea ch, o by he ac ha he e is
a p ominen jou nal de o ed o i . Two majo ( ecen ly e ised)
assump ions in e olu iona y biology ha e u he con ibu ed
o he cen ali y o he placen a in he concep ualiza ion o
p egnancy. One o hem is he iden i ica ion o he e olu ion
o mammals wi h ha o he placen a. In ac , he naming
o Eu he ia as “placen al mammals” no only gi es he w ong
imp ession ha he placen a is unique o eu he ians, when
also ma supials ha e one (Ren ee, 2010). I also sugges s
ha he placen a is he key inno a ion in he e olu ion o
eu he ian p egnancy. Al oge he hey seem o con end ha
he majo e olu iona y changes owa ds i ipa i y occu ed
solely on he emb yonic side. The o he assump ion conce ns
he iew ha “in asi e placen a ion” has deepened in e olu ion.
The e is a g ea di e si y o placen al ypes among eu he ian
species, wi h di e en deg ees o pene a ion in o he u e ine
wall; om supe icial placen as, whe e se e al ma e nal and
e al issue laye s sepa a e he ma e nal and e al blood, o
highly imb ica ed o ms o placen a ion (so-called hemocho ial)
whe e e al issues a e exposed di ec ly o ma e nal blood.
Since Haeckel’s imes un il e y ecen ly, he belie in
e olu iona y biology has been ha ea ly eu he ian species
had supe icial placen as, and ha “in asi e placen a ion” is
he mos de i ed o m o emale-emb yo in e ac ion (see
Wildman e  al., 2006, o e e ences).
3
The placen a e ol ed om he ascula ized memb anes o he yolk sac and/
o allan ois, which in o ipa ous animals supply nu ien s om yolk and gas
exchange wi h he ex e nal en i onmen . In con as , in i ipa ous mammals
he memb anes use wi h he cho ion o o m he placen a, which a aches o
he u e ine wall and se es as con inuous media o o nu ien s and gas exchange
wi h he ma e nal blood (Ramsey, 1982; Ca e , 2012).
Nuño de la Rosa e al. P egnan Females as His o ical Indi iduals
F on ie s in Psychology | www. on ie sin.o g 3 Janua y 2021 | Volume 11 | A icle 572106
Vi ipa i y o li e-bea ing ep oduc ion is a widesp ead
ep oduc i e mode ha has a isen independen ly in many
lineages o in e eb a e as well as e eb a e animals (Wake,
2004), he la e including no only mos mammals bu also
se e al clades o ishes, amphibians, and ep iles. Ye , despi e
a clea ly eu he ian-domina ed iew o i ipa i y ha
unde es ima es o he o ms o i ipa i y (Blackbu n, 2015),
webelie e ha he emphasis on he con inui y be ween o ipa i y
and i ipa i y in mammals has con ibu ed o blu ing some
o he special cha ac e is ics o eu he ian p egnancy. The
pe cep ion o p egnancy as de i ed om o ipa i y by a simple
spa ial in e naliza ion ollowed by he g adual e olu ion o
in asi e placen a ion, suppo s an in e p e a ion o eu he ian
ep oduc ion as a me e supe imposi ion o he emb yo’s
physiology on he ma e nal physiology, and con ibu es o he
ea men o mo he and emb yo as semi-independen en i ies
(Abbo and Rokas, 2017), and pa icula ly o ha o he p egnan
emale as a con aine o which he emb yo is me ely a ached
o nu i ion.
This na a i e abou he phylogeny o p egnancy se s he
g ound o he second majo componen o classical
e olu iona y na a i es o eu he ian ep oduc ion, namely
he iew o p egnancy as an e olu iona y s a egy in ol ing
cos s and bene i s o pa en s and o sp ing. In his ame,
he explana ion o he ansi ion om o ipa i y o i ipa i y
in mammals weighs he i ness cos s and bene i s o his
ansi ion o he emale and he o sp ing, ea ing hem
as di e en uni s o selec ion (see C espi and Semeniuk,
2004; Bainb idge, 2014, o e iews). In gene al, he
in e naliza ion o de elopmen p o ided by i ipa i y is
sugges ed o ha e majo ad an ages o he o sp ing (such
as inc eased su i o ship by a oiding he ulne able egg
s age, inc eased bi h size, and o sp ing igo due o p olonged
ma e nal p o isioning), while en ailing a mix u e o ad an ages
and cos s o emales. Ad an ages include g ea e mobili y
and smalle eggs, which a e less cos ly o disca d when
un e ilized. The cos s ange om educed o aging abili y
and highe suscep ibili y o p eda ion du ing p egnancy, o al
b ood loss upon dea h, highe ene ge ic cos s, lowe ecundi y,
and lesse abili y o in e up he ep oduc i e p ocess and
disca d he o sp ing when condi ions change ab up ly. In
sum, one should no conside ha i ipa i y cons i u es a
good solu ion o bo h mo he s and o sp ing in e olu iona y
adap i e e ms (A ise, 2013).
The non-op imali y o he “p egnancy solu ion” is explici
in a well-known hypo hesis on he e olu ion o p egnancy,
he so-called “con lic hypo hesis”, which con on s he iew
o p egnancy as a “coope a i e in e ac ion be ween a mo he
and he e us” and poin s ins ead o he po en ial o con lic ing
“in e es s” be ween ma e nal and e al genes (Haig, 1993,
p. 495; see also Haig, 1996). As a consequence, he gene ic
in e es s o mo he s and emb yos, unde s ood as di e en
indi iduals, a e no pe ec ly aligned. The easoning o his
comes om Hamil on’s concep o inclusi e i ness, ollowing
which he calcula ion o he i ness o an indi idual is ob ained
by adding he i ness con ibu ion o ela i es, weighed by
he ela edness, o he di ec e ec s on i ness. Gi en ha
mo he s a e likely o bemo e ela ed o hei u he o sp ing
han he cu en emb yo (as cu en and u u e o sp ing
may ha e di e en a he s), ma e nal in es men in cu en
p egnancy is expec ed o belowe han he emb yo’s. Acco ding
o Da id Haig, emb yonic genes will hus be selec ed o
gaining mo e nu ien s om he mo he , whe eas ma e nal
genes will be selec ed o limi ha ans e . The s onges
e idence in a o o gene ic con lic a e imp in ed genes (i.e.,
hose in which exp ession o alleles depends on he pa en -
o -o igin) in he placen a. The hypo hesis p edic s ha pa e nal
alleles will ollow he in e es s o he emb yo, and inc ease
ma e nal in es men and/o p olong p egnancy, whe eas he
e ec s o ma e nal alleles will align wi h ma e nal in e es s
and educe in es men . F om his pe spec i e, “ he pa en -
o sp ing con lic o e he deg ee o pa en al in es men ” is
widely seen as “ he main selec i e ac o in he e olu ion o
ep oduc ion” (Lodé, 2012, p. 259).
All in all, he e olu iona y iew o p egnancy as a locus
o con lic whe e he emb yo a emp s o “manipula e” he
mo he (see C espi and Semeniuk, 2004) con o ms wi h
adi ional app oaches o he physiology o p egnancy.
Biological and biomedical accoun s o p egnancy o en p esen
i as a con lic ual ela ionship be ween wo independen
en i ies, a “ba le,” o a “comba ” (Asha y e al., 2018) whe e
he emb yo uses “a a ie y o coe ci e ac ics” (Asha y e al.,
2018) o “manipula e” (C espi and Semeniuk, 2004) and
“in ade” he mo he . As a consequence, he ole o he mo he
is o en s ill p esen ed as a passi e o de ensi e one, as
e lec ed in he biomedical depic ions o he immune eac ion
o p egnan emales upon implan a ion (Mo , 2007). Immune
esponse in p egnan emales would be expec ed o wo
easons: i s , because he emb yo b eaches physical issue
in eg i y du ing implan a ion, and second, because his
wounding is caused by a issue which is immunologically
di e en om he emale. Howe e , as he e is no ma e nal
ejec ion o he emb yo, adi ional app oaches ha e aimed
o unde s and how he expec ed ma e nal immune eac ion
o implan a ion is “supp essed” by he e us, o example
ia he manipula ion o p oges e one p oduc ion, hus leading
o an “immunological indolence o ine ness o he mo he ”
(Medawa , 1953; see S ad maue and Wagne , 2020a,b and
e e ences he ein).
The explana ions o p egnancy as an e olu iona y s a egy
in ol ing cos s and bene i s o pa en s and o sp ing, in
con inuous con lic o e p o isioning, and in which he emale
is manipula ed by he emb yo agains he in e es s, ein o ce
he iew o p egnancy as in ol ing wo sepa a e indi iduals
ollowing hei own in e es s, a he han as a ep oduc i e
p ocess p omo ing cons uc i e ela ions be ween mo he and
o sp ing. None heless, his iew o p egnancy as a con lic
is no he only possible iew o p egnancy as an e olu iona y
s a egy. Indeed, ecen models ha e p oposed ha co-adap a ion
( a he han con lic ) be ween genes exp essed in mo he and
hose exp essed in o sp ing has played a majo ole in he
e olu ion o p egnancy and may o e a complemen a y
explana ion o imp in ed genes (Wol and Hage , 2006). While
he ea men o ma e nal and o sp ing i ness in e es s in
Nuño de la Rosa e al. P egnan Females as His o ical Indi iduals
F on ie s in Psychology | www. on ie sin.o g 4 Janua y 2021 | Volume 11 | A icle 572106
con lic heo ies concei es hem as ha ing sepa a e in e es s,
he coadap a ion models assign a i ness ad an age o he
in e ac ion i sel , namely, o p egnancy. In e es ingly, in hese
models he i ness in e es s o mo he s and emb yos a e no
only aligned, bu a e in e dependen , i.e., i ness ad an ages
o he mo he depend on he co-e olu iona y change in
he e us.
In sum, eu he ian p egnancy has been s udied om he
pe spec i e o he e being wo sepa a e indi iduals, each wi h
hei own in e es s in e olu ion. As we a gue in he ollowing
sec ion, e o-de o s udies o p egnancy suppo an al e na i e
pe spec i e which, ins ead o assuming ha he esul s o
ep oduc ion (i.e., sepa a e indi iduals) al eady ope a e in
p egnancy, claims o an al e na i e indi idua ion o p egnancy
as he locus o de elopmen al ep oduc ion. In he con ex o
he e olu ion o eu he ian ep oduc ion, his new kind o
ep oduc i e sys em cons i u es wha we will call a his o ical
indi idual. F om his pe spec i e, i will be shown ha he
con lic models pic u ing mo he s and emb yos as dis inc
e olu iona y indi iduals o e a pa ial accoun o he indi iduali y
o p egnancy, no only om he pe spec i e o “p oxima e”
disciplines such as physiology o de elopmen al biology, bu
also om an e olu iona y s andpoin .
EVO-DEVO OF PREGNANCY
The way ep oduc ion is conside ed in he neo-Da winian
adi ion is he consequence o a long his o ical ajec o y o
wo k ein o cing he iew ha he ansmission o he i able
a ia ion occu s independen ly o , and p e iously o,
de elopmen . As a consequence, ep oduc ion has been
conside ed o consis mainly o he p oblem o eplica ion,
o en educed o a o mal p ocess o copy-making o a me e
ansmission o in o ma ion (Dawkins, 1982). Howe e , in he
las decades, philosophe s and e olu iona y biologis s ha e
denounced ha ep oduc ion is a lo mo e complex han
eplica ion, as i en ails he ma e ial ans e o pa s om
pa en s o o sp ing (Ma u ana and Va ela, 1987; G ieseme ,
2000a, 2005), as well as he econs uc ion, a he han he
me e ansmission, o pheno ypes (Jablonka, 2004; Gilbe and
Epel, 2008).4 The e o e, ep oduc ion and de elopmen canno
be dis inguished so easily, inso a as he e-p oduc ion o
o ganisms is ega ded as a ma e ial, o ganiza ional and
de elopmen al p ocess, in ol ing bo h he ans e o pa s
and he in e play o a pleiad o bio ic and abio ic ac o s
which, in he case o p egnancy, include he ac i e ole o
4
While he e ha e been ecen a emp s o imp o e he unde s anding o
ep oduc ion om a Da winian pe spec i e, hey s ill ega d eu he ian
ep oduc ion essen ially as he capaci y o make eliable copies o an indi idual
en i y. Fo ins ance, God ey-Smi h’s (2015) ecen dis inc ion o di e en
o ms o ep oduc ion classi ies eu he ian mammals as “collec i e” ep oduce s
which, jus like any o he mul icellula , ha e pa s wi h he capaci y o
ep oduce, while i uses a e seen as “sca olded” ep oduce s whose ep oduc ion
depends on ex e nal esou ces. In con as , om he ep oduce s pe spec i e,
almos all cases o ep oduc ion a e seen as sca olded (G ieseme , 2014a,b;
Minelli, 2016).
emales in he de elopmen al ep oduc ion o hei o sp ing.
In his sense, ou iew o ep oduc ion ollows many impo an
philosophical discussions ha ha e emphasized he impo ance
o a de elopmen ally minded and diach onically cons uc i e
iew o on ogeny (Oyama, 2000), as well as he ac i e ole
o o ganisms as adap i e agen s in e olu ion (Walsh, 2015).
Despi e he heo e ical pleas o conside ing he ma e iali y
o ep oduc ion, he e olu ion o modes o ep oduc ion has
emained la gely unexplo ed so a . As Fusco and Minelli (2019)
ha e ecen ly denounced, “gene aliza ions o he phenomenon
o ep oduc ion” may “ha e hidden he di e si y o ep oduc i e
phenomena equen ly ound e en among closely ela ed axa”
(p. xiii). One u he in luencing ac o o his may be ha
he ield o e o-de o has ended o ocus on he e olu ion o
body pa s a he han on he e olu ion o ela ions among
o ganismal en i ies o o new kinds o biological indi iduali ies.
Ye , in he las decade, s udies on he “e o-de o o ep oduc ion”
ha e s a ed o e e his end. Unde his pe spec i e, modes
o ep oduc ion a e no only ega ded as di e en s a egies
o maximizing i ness, bu also as ma e ial de elopmen al
p ocesses in ol ing he ans o ma ion o complex ela ions
among o ganismal en i ies. In he emainde o his sec ion,
wep esen some esul s o ecen e o-de o s udies o eu he ian
ep oduc ion and show how hey suppo a concep ion o
p egnancy ha , in a ibu ing a cen al impo ance o he
e ol ed ac i e ma e nal ole and he ela ional no el ies o
p egnancy, signi ican ly di e s om he one p esen ed in he
p e ious sec ion.
Recen s udies emphasize ha he e olu ion o p egnancy
in ol ed c ucial inno a ions on he emale side as a o m o
e olu iona y eaccommoda ion (S ad maue and Wagne , 2020b).
The o igin o a new kind o in eg a ion be ween mo he and
emb yo en ailed an in eg al ea angemen o he in e ac ions
among he main physiological sys ems o he emale, namely
he ne ous sys em (b ain and neu oendoc ine changes), he
ca dio ascula sys em (inc eased blood olume, dec ease in
hemoglobin concen a ion, and inc eased coagula ion), he
locomo o sys em (skele omuscula changes in backbone, pel is,
and gai ), and he immune and me abolic con ol sys ems
(e.g., p o ein me abolism, and kidney capaci y), o name a
ew (Bainb idge, 2014). All hose e-accommoda ions in ol e
a coe olu ion o ex ensi e in e dependencies be ween mo he
and o sp ing, bo h sides hus o ming an e ol ing ela ional
uni (e.g., Knoe le , 2010; E lebache , 2013; Mo e and Colucci,
2014; Pa liče e al., 2017). As wehighligh ed in he p e ious
sec ion, p e ious s udies ha e abundan ly ocused on he
e olu ion o he placen a. In con as , e o-de o s udies e eal
ha he o igin o eu he ian p egnancy in ol ed c ucial ela ional
inno a ions on bo h he emb yo and he ma e nal side. This
esea ch also coun e ac s he ecei ed iews o p egnancy as
a supe icial kind o in e naliza ion in which he mo he signi ies
a o m o a li ing shel e o he emb yo.
On he emb yo side, while he placen a has o igina ed
mul iple imes in e olu ion (Ren ee, 2010; Robe s e  al.,
2016), he kind o placen a ion o igina ing in he s em lineage
o Eu he ia is unique, in pa icula wi h ega d o he deg ee
o ma e nal- e al in eg a ion i con e s (Wildman e al., 2006).
Nuño de la Rosa e al. P egnan Females as His o ical Indi iduals
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Eu he ian placen a ion b eaches ma e nal in eg i y and is
associa ed wi h implan a ion. In s a k con as o
non-mammalian i ipa ous animals in which he placen a is
only apposed o he u e ine epi helium, he ma e nal-placen al
in e ace o eu he ian mammals e odes he u e ine epi helium
o e en he ma e nal essel walls. As wesaw in he p e ious
sec ion, he ecei ed assump ion on he e olu ion o he
placen a was ha in asi e placen a ion e ol ed om supe icial
placen as wi h a shallow con ac be ween he ma e nal and
he emb yonic issues. In con as , phylogene ic analyses ha e
ecen ly shown ha he in asi e placen al ype was indeed
he ances al s a e o all eu he ians, indica ing ha eu he ian
p egnancy a ose concomi an ly wi h he o igin o a highly
en angled ma e nal- e al in e ace (Mess and Ca e , 2006;
Wildman e  al., 2006).
On he ma e nal side, ecen esea ch has e ealed ha new
specialized cell ypes, such as he decidual s omal cell, he
u e ine na u al kille cell, and a specialized o m o esiden
mac ophages, e ol ed likely coinciden ally wi h he e olu ion
o p egnancy (Wagne e al., 2014; E kenb ack e  al., 2018).
Pa icula ly in e es ing is he decidual s omal cell ype, which
e ol ed oge he wi h in asi e placen a ion (Cha an e al., 2016;
E kenb ack e al., 2018). These ma e nal no el ies likely enabled
sus ained implan a ion and he e o e he e olu ion o he i s
s ep owa ds eu he ian p egnancy. Jus like in he case o he
placen a, he no el y o he u e ine cells elies no only on
hei inhe en cha ac e is ics, bu on hei ela ional abili ies,
ha is, on hei capaci ies o communica e wi h o he (in his
case, gene ically he e ogeneous) cells (see G i i h and Wagne ,
2017). Indeed, impai ed decidualiza ion o endome ium has
been shown o in e e e wi h emb yo-ma e nal in e ac ions in
humans, hus causing ecu en p egnancy loss (Salke e al., 2010).
C ucial o his new unde s anding o he ela ional no el ies
eme ging in eu he ian ep oduc ion ha e been he s udies on
he ole o in lamma ion in he o igina ion and p olonga ion
o p egnancy. P egnancy has been adi ionally desc ibed by
ep oduc i e biologis s as a pe iod be ween wo disc e e e en s,
implan a ion and bi h, bo h o which ha e been shown o
en ail in lamma ion (Mo , 2007; Mo and Ca denas, 2010; Mo
e  al., 2011). Whe eas in ma supials he in lamma ion caused
by he i s con ac o he e ilized egg is ollowed by expulsion
(bi h), and hus he pe iod o p egnancy is e y sho , in
eu he ian mammals in lamma ion is a equi ed s ep o success ul
implan a ion and does no esul in immedia e bi h. In eu he ian
p egnancy, he in lamma o y esponse is hus modi ied by he
ma e nal decidual cells o sepa a e in lamma o y implan a ion
om expulsion (Cha an e  al., 2016; G i i h e  al., 2017).
Thus, he ma e nal immune sys em is no simply supp essed.
Ra he , he e olu ion o decidual cells enabled i s empo ally
and spa ially local modi ica ion, making implan a ion possible
(Mo and Ca denas, 2010; Mo e al., 2017)5 and subsequen ly
expanding p egnancy and main aining an al e na i e s able
homeos a ic s a e. This sequence o e en s in eu he ians e ol ed
5
I is impo an o no e ha he modi ica ion o he immune eac ion mus
be local, no sys em-wide o pe sis en , because i would o he wise likely
be le hal o he mo he .
a e he las common ances o wi h ma supials, who do no
ha e decidual cells and eac o a achmen wi h expulsion.
The eu he ian no el y hence consis s o he no el cell ype
enabling a p olonged in au e ine de elopmen al s age o
be “inse ed” be ween wo in lamma o y e en s, namely
implan a ion and bi h (G i i h e al., 2017; E kenb ack e  al.,
2018; see Figu e 1).
In he nex sec ion, we p esen ou main claim ha he
e olu iona y modi ica ions ha led o he o igina ion o
p egnancy ( emale in eg al eaccomoda ion, eme gence o a
new ype o placen a ion and u e ine cell ype, and modi ica ion
and epu posing o in lamma ion) may be in e p e ed as a
ansi ion in indi iduali y in which wo indi idual p ocesses,
he adul emale and he de eloping emb yo, a e me ged in o
a single ep oduc i e indi idual o a his o ical kind.
PREGNANT FEMALES AS HISTORICAL
INDIVIDUALS
The ea u es o he e olu ion o eu he ian ep oduc ion as
e iewed in he p e ious sec ion p omp us o p opose ha
p egnan emales cons i u e a new kind o indi idual appea ing
in e olu ion. In his sec ion, weexamine some o hese ea u es
in he ligh o concep ual wo k on his o ical kinds de eloped
in he ield o e o-de o, and a gue ha p egnan emales can
be conside ed o be biological indi iduals o his his o ical
kind. The no ion o his o ical kind has been cha ac e ized as
including “a subse o na u al kinds ha acqui es, h ough
e olu iona y p ocesses, a quasi independen lineage-his o y”
(Wagne and Tomlinson, 2020, p. 1). His o ical kinds “ha e
a de ini e beginning and po en ially an end” (Wagne , 2001,
p. 10) and, he e o e, allow o combine in he same concep ,
as wo sides o he same coin, he e olu iona y o igina ion
o new p ocesses, s uc u es and unc ions, and hei his o ical
pe sis ence h oughou e olu iona y ime.
FIGURE1 | Vi ipa i y is a sha ed de i ed ai o ma supials and eu he ians.
Emb yo implan a ion, in asi e placen a ion, and decidual s omal cells (DSC)
occu only in he eu he ian lineage [Adap ed om Wagne e al. (2019),
Figu e1, p.2].

Nuño de la Rosa e al. P egnan Females as His o ical Indi iduals
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Unde s anding indi iduali y as a his o ical kind encompasses
a se o c i e ia o indi idua ion o e olu iona y en i ies used
in he con ex o e o-de o. The c i e ia used in his ield o
ack he his o ical eme gence and pe sis ence o en i ies such
as homologues and body plans, di e om he adi ional
c i e ia o e olu iona y indi idua ion, and enable e o-de o
biologis s o indi idua e e olu iona y uni s in dis inc ways.
E olu iona y en i ies in e o-de o ha e been mainly
concep ualized as ypes o na u al kinds (see Wagne , 1996;
B igand , 2017, o a e iew), and he e wep opose o ex end
his iew o kinds o indi iduals. While his pe spec i e has
classically been applied o he indi idua ion o body pa s,
such as e eb a e limbs o cell ypes, i has also been ex ended
o include de elopmen al s ages (e.g., la al s. adul s age),
physiological p ocesses (e.g., mens ua ion o o ula ion), o
unc ions (e.g., beha io s; see, e.g., Gilbe and Bolke , 2001;
Schol z, 2005; Lo e, 2007). We a gue ha he c i e ia o
his o ical indi idua ion can be u he applied o en i ies a ising
in ep oduc i e ela ions, and enable a iew o he p egnan
emale as a new kind o indi idual, namely a his o ically
new, semi-independen ly modi iable de elopmen al s age in
he li e cycle o (some) eu he ian emales, wi h con inuous
pe sis ence since i s o igina ion.
C i e ia o His o ical Kinds
His o ical uni s a e e ol ed en i ies o p ocesses which ul ill
ce ain c i e ia ha allow us o ecognize hem as dis inc ,
namely, hei con inuous pe sis ence ac oss axa and h oughou
e olu iona y ime, and hei non-exchangeabili y wi h o he
such uni s. As we will see, p egnancy can be in idua ed in
his way because i ul ills hese wo c i e ia.
The i s c i e ion o ack his o ical indi iduals, pe sis ence,
does no de i e om he di ec eplica ion o an en i y (such
as a limb o a cell), bu a he om hose de elopmen al
p ocesses ha accoun o he his o ical con inui y o an en i y
wi hin and ac oss species. As a consequence o hei
de elopmen al au onomy, hese en i ies can change o emain
s able h oughou e olu ion somewha independen ly om
o he s (Wagne and Al enbe g, 1996). The classical example
is he e eb a e limb, which adop s di e en shapes and sizes
ac oss e eb a es, adap ed o di e en unc ions, bu i ye
pe sis s as a dis inc , de elopmen ally g ounded, his o ical kind.
The p egnan emale as a his o ical indi idual e okes an
e olu iona ily pe sis en en i y in which emale and emb yo
a e de elopmen ally en angled. This is mani es in he o m
o a ansien , bu empo ally dema ca ed, indi iduali y
cha ac e ized by a high deg ee o in eg a ion be ween emale
and emb yo. As a gued in he p e ious sec ion, he o igina ion
o p egnancy en ailed a majo modi ica ion o he ela ional
abili ies o mammalian emales, one ha allowed p egnan
emales o in e nalize emb yos as pa s o a new ep oduc i e
sys em. The in lamma o y e en s ollowing implan a ion and
p eceding bi h indi idua e p egnancy in ime: bo h he onse
and inaliza ion o p egnancy a e coo dina ed ela ional e en s
be ween mo he and emb yo, a he han occu ing when he
emb yo one-sidedly eaches ce ain s ages o de elopmen o
ma u a ion. In his ame, ep oduc ion is hus ea ed less as
a poin e en in he li e ime ma ked by e iliza ion, and mo e
as being i sel a de elopmen al p ocess. This diach onic iew
o his o ical indi iduali y as applied o he ep oduc i e phase
o p egnancy aligns, as sugges ed o us by an anonymous
e iewe , wi h ecen wo k on he biology o ep oduc ion
(Fusco and Minelli, 2019), whe e biological indi iduali y is
d a ed wi hin he amewo k o li e cycle e olu ion (DiF isco
and Mossio, 2021).
Mo eo e , he pe sis ence and dis inc i eness o his o ical
indi iduals a e no only e lec ed in hei e olu iona y con inui y
bu also in hei dis inc i e abili y o e ol e. The e o e, as
a consequence o indi idua ion, eu he ian p egnancy ob ains
a ce ain deg ee o e ol abili y on i s own, inso a as i
inaugu a es new ways o gene a ing a ia ion and he e o e
new po en ial o e ol e. The ela i e abili y o he p egnan
emale o e ol e as a uni is e lec ed, o example, in he
a iabili y o eu he ian species in he leng h o ges a ion, o
in he cha ac e is ic di e si ica ion o he ma e nal-placen al
in e ace (Ca e and Ende s, 2004).
The second c i e ion o his o ical indi iduali y,
non-exchangeabili y, cap u es he idea ha he e olu iona y
au onomy o a new his o ical en i y does no esul om he
disconnec ion o his en i y om o he s, bu a he om an
e olu iona y p ocess o compensa ion and accommoda ion o
de elopmen al and physiological in e dependencies wi hin he
o ganiza ion o a body plan, hus esul ing in a new kind o
e ol ed in eg a ion. Fo example, i e eb a e hind limbs can
be indi idua ed as his o ical indi iduals i is no only because
hey change independen ly o o elimbs (and o e e y hing
else), bu because hey a e non-exchangeable. The eason is
ha , al hough hey de elop using some o he same genes
and de elopmen al pa hways, hindlimbs a e di e en (and e ol e
di e en ly) om o elimbs also due o hei in eg a ion in he
dis al pa o he e eb a e body. In con as , human hai s
canno be conside ed as his o ical indi iduals: while hey a e
physically independen en i ies, hey a e “exchangeable” in he
sense ha he iden i y o each hai does no depend on hei
pa icula loca ion in he skin. The dis inc i eness o his o ical
kinds is hus based bo h in hei e olu iona y au onomy and
in hei e ol ed in eg a ion wi hin he sys em hey belong o.
F om his pe spec i e, he mode o e olu ion ins an ia ed
by he in eg al eaccommoda ion o all he physiological sys ems
ha make up eu he ian ep oduc ion (including he emb yo)
is no su p ising. E olu ion is a p ocess in which new ai s
and ela ions eme ge no by me e addi ion o new de elopmen al
s ages o s uc u es on op o he p eexis ing, conse ed ones,
bu by he ec ui men , modi ica ion and in eg a ion o he
old in o a new con ex (Albe ch, 1985). Classic models in
e eb a e e o-de o include s udies on he o igin and e olu ion
o pha yngeal jaws, which in ol ed he in eg a ion o changes
in he isual, neu al, skele al, muscula , and beha io al sys ems.
In he wo ds o B ian Hall, “[s]uch s udies mo e us away
om iden i ica ion o single key inno a ions and owa d an
emphasis on in eg a ed changes and on ogene ic epa eming
in in e ela ed sys ems” (Hall, 1998, p. 282). As we saw in
he p e ious sec ion, he no el y o p egnancy no only en ailed
he eme gence o new ela ional s uc u es, p ocesses, and
Nuño de la Rosa e al. P egnan Females as His o ical Indi iduals
F on ie s in Psychology | www. on ie sin.o g 7 Janua y 2021 | Volume 11 | A icle 572106
unc ions, bu also he modi ica ion o a ange o p e-exis ing
physiological sel -main aining sys ems o suppo a dis inc ly
new homeos a ic s a e ha inco po a es he implan ed emb yo
(Pa liče e al., 2017). The e o e, he indi idua ion o p egnancy
does no occu by decoupling p egnancy om he es o
emale biology, bu a he by he unique modi ica ions o emale
physiology (i.e., capaci y o changes in immune, me abolic,
and locomo o y sys ems) ha enable p egnancy and hence
in eg a e i wi h o he de elopmen al s ages in i s li e cycle.
This in eg a ion includes he accommoda ion o he emb yo,
as e lec ed in he e olu ion o he emale immune sys em.
In gene al, wo e olu iona y “solu ions” o a con lic ing si ua ion
(such as ha igge ed by he dis up ion o issue in eg i y
caused by emb yo implan a ion) could be conside ed. One
migh consis o emo ing he o igin o he con lic en i ely,
and he o he o in eg a ing and modi ying i .6 In con as
wi h he ecei ed unde s anding o p egnancy as an ongoing
con lic , e o-de o s udies o he o igin o p egnancy sugges
ha implan a ion leads o a c i ical dis up ion o physiological
homeos asis (E kenb ack e al., 2018), ollowed by i s o e coming,
which esul s in a no el homeos a ic s a e de ined a he
ela ional le el. I is his new unc ion and he associa ed
de elopmen al and physiological p ocesses ha e o-de o s udies
o eu he ian ep oduc ion aim a explaining.
The O igin o P egnan Females as
His o ical Indi iduals
In con as wi h he mos p ominen wo k om he
neo-Da winian pe spec i e on p egnancy, e o-de o s udies o
eu he ian ep oduc ion conce n he e olu iona y o igina ion,
a he han he modi ica ion, o p egnancy. In his sec ion,
we a gue ha he kind o ans o ma ions in ol ed in his
ansi ion is no simply assimilable o an e olu iona y no el y
wi h an associa ed new unc ion, as in he o igin o cha ac e s
such as ea he s o pai ed ins. Ra he , he o igin o p egnancy
has meaning ul co espondences wi h majo ansi ions such
as he o igin o euka yo ic cells o mul icellula s, which o en
en ail new modes o ep oduc ion (G ieseme , 2000b) and he
eme gence o new le els o e olu iona y indi iduali y (Buss,
1987; Michod, 2000).
On a i s glance, he case o p egnancy does no seem
o i in he s anda d iew o majo ansi ions (Mayna d
Smi h and Sza hma y, 1997): unlike euka yo ic cells o
mul icellula o ganisms, p egnan emales ce ainly do no
ep oduce di ec ly in o p egnan emales. Howe e , he sys emic
ans o ma ions and he adical changes in ep oduc i e
capaci ies expe ienced by eu he ian emales indica e ha he
o igin o p egnancy had u he e olu iona y implica ions
han ha o a new ep oduc i e cha ac e . In pa icula , he
o igin o eu he ian ep oduc ion did en ail ha “en i ies ha
we e capable o independen ep oduc ion be o e he ansi ion,
can ep oduce only as pa s o a la ge whole a e i ”
6
Wagne and co-au ho s go a s ep u he o sugges ha s ess pa hway-
inducing p ocesses o e a pa icula ly s ong oppo uni y o gene a e no el ies,
by i s in e nalizing, and hen modi ying an o iginally plas ic s ess esponse
(E kenb ack e  al., 2018; Wagne e  al., 2019).
(G ieseme , 2000b, p. 79). In his sense, he ansi ion o
p egnancy migh beconside ed as analogous o he ansi ion
o he euka yo ic cell, desc ibed by God ey-Smi h (2015,
p.10123) as he e en in which “ wo simple ep oduce s gi e
ise o collec i e ep oduc ion, ollowed by a loss o ep oduc i e
au onomy and he endosymbion mo ing owa ds sca olded
ep oduc ion.” In an analogous way, eu he ian p egnancy
en ailed a loss o ep oduc i e au onomy a he le el o he
egg, bu a gain o ep oduc i e capaci y a he new indi idual
le el cons i u ed by he p egnan emale. In his sense, p egnancy
can be conside ed as a las o he successi e e olu iona y
s ages o emale in eg a ion o ep oduc ion: om eleasing
an un e ilized egg o be e ilized and de eloped ex e nally,
o in e nal e iliza ion ollowed by a la gely ex e nal
de elopmen (i.e., o ipa i y), o me a he ian i ipa i y, in
which case bo h e iliza ion as well as g ea pa o de elopmen
a e inco po a ed wi hin he emale’s body. This in eg a ion
impo an ly a ies in ex en and ime: in some mammalian
species, de elopmen has e ol ed o become in eg a ed wi h
ep oduc ion un il a ce ain s age (ma supials, hose wi h an
ex emely sho ges a ion pe iod), while he ex ension o
p egnancy has allowed eu he ians o in eg a e de elopmen
and ep oduc ion un il a much la e s age. In eu he ians,
de elopmen and ep oduc ion ha e become highly in eg a ed
p ocesses, inso a as he ep oducing indi idual ( he p egnan
emale) needs o pa icipa e in he de elopmen o i s o sp ing
o achie e i s own ep oduc ion. To sum up: p egnan emales
o m unique indi iduals, ela ing wo de elopmen al p ocesses
a di e en s ages o hei li e his o ies. They a e ep oduc i e,
ela ional, and ansien indi iduals, al hough, like mos
biological indi iduals, hey ha e a beginning and an end:
hey a e bo n a implan a ion and end a bi h.
In philosophical e ms, he concep o his o ical indi idual
as applied o p egnan emales deli e s a new insigh o he
no ion o biological indi idual, one which is dis inc ly
e olu iona y and which di e s om he con lic models. As
poin ed ou in he in oduc ion, philosophical deba es on
biological indi iduali y ha e oo o en been posed in e olu iona y
e ms o he de imen o o he biological ields (P adeu, 2016a,
p. 765). Howe e , i is impo an o s ess ha he implica ions
o indi iduali y o non-selec ionis , de elopmen al app oaches
o e olu ion ha e been also neglec ed. The hesis ha p egnan
emales a e his o ical no el indi iduals elies on an e olu iona y
s ance, ye i is a e y di e en one wi h ega d o p e ious
selec ionis accoun s. In he ollowing sec ion, he main concep s
o indi iduali y discussed in he philosophy o biology a e
e iewed and compa ed acco ding o hei adequacy o accoun
o p egnancy in con as o he his o ical no ion ad anced he e.
PREGNANCY AND BIOLOGICAL
INDIVIDUALITY
The na u e o biological indi iduali y has been a opic o in ense
inqui y in he philosophy o biology o he las decade (Ruiz-
Mi azo e al., 2000; Cla ke, 2010; P adeu, 2016a; DiF isco, 2019),
whe e ecei ed assump ions ha e been e ised o espond o
Nuño de la Rosa e al. P egnan Females as His o ical Indi iduals
F on ie s in Psychology | www. on ie sin.o g 8 Janua y 2021 | Volume 11 | A icle 572106
new challenges coming om en i ies ha do no con o m o
adi ional concep s o indi iduals conside ed as homogeneous,
unique and unc ionally in eg a ed en i ies (San elices, 1999).
Inso a as ep oduc ion is gene ally ega ded as he p ocess
by which new indi iduals a e gene a ed, he no ion o
indi iduali y plays an ine i able cen al ole in s udies on
ep oduc ion (Fusco and Minelli, 2019, p. 25). Howe e , despi e
his appa en cen ali y o indi iduali y in ep oduc ion,
p egnancy has no ecei ed much a en ion in he con ex o
his deba e. Recen ly, Kingma (2019b) has en a i ely discussed
how some c i e ia o biological indi iduali y ( aken om
Cla ke, 2010) may apply o he en i ies in ol ed in mammalian
p egnancy. Kingma does no de end hese c i e ia o hei
applica ion, bu poses “[ ]he me i o he exe cise in aising
he ques ion.” In con as , in his pape , we do ake a s ance
o a gi en unde s anding o biological indi iduali y in he
case o p egnancy. In his sec ion, we con as ou p oposal
o p egnancy as a his o ical kind o indi idual wi h he h ee
co e concep s o biological indi iduali y cu en ly discussed
in he philosophy o biology, namely he physiological, he
e olu iona y, and he ecological app oaches, and conside hei
me i s and sho comings as applied o he indi iduali y o
eu he ian p egnancy (see Table 1).
Physiological Indi iduali y
The physiological no ion o indi iduali y cap u es he mos
in ui i e iew o biological indi iduals as au onomous,
unc ionally in eg a ed, and sel -main aining sys ems, sepa a ed
om hei en i onmen s. I unde lies he classical iews o
“o ganisms” de eloped by he physiological adi ion in
biomedicine (e.g., Pe lman, 2000), as well as he o ganiza ional
app oach in con empo a y philosophy o biology (Ruiz-Mi azo
e al., 2000; Mo eno and Mossio, 2015). C i e ia o physiological
indi idua ion comp ehend how di e en unc ionali ies con ibu e
o sel -main enance. Mo e ecen ly, hey ha e been expanded
o include how immune mechanisms enable he delinea ion
and pe sis ence o physiological indi iduals (P adeu, 2010, 2016b).
F om he physiological pe spec i e ha guides biomedical
and bioe hical app oaches o human p egnancy, i is gene ally
conside ed ha p egnancy encompasses wo sepa a e o ganisms,
namely, he mo he and he emb yo. While he s a us o mo he s
as physiological indi iduals is gene ally seen as i ially
uncon o e sial, he e is no consensus conce ning he s age a
which emb yos begin o ha e a sepa a e indi idual exis ence
in de elopmen . Di e en de elopmen al e en s ha e been
p oposed o ma k he ansi ion o physiological indi iduali y
in human emb yos, including e iliza ion (Damschen e  al.,
2006), implan a ion (Al a gonzález, 2016), gas ula ion (Smi h
and B ogaa d, 2003), o comple ion o o ganogenesis (Nuño
de la Rosa, 2010). In con as , ecen con ibu ions ha e challenged
he assump ion ha emales p ese e a physiological indi iduali y
independen o hei o sp ing du ing p egnancy. As men ioned
be o e, Howes (2008) concluded ha immune in e ac ions blu
he adi ional bounda ies assumed be ween mo he and o sp ing,
and o e ed a hi d ela ional, “no -one-bu -no - wo,” al e na i e
emphasizing he dynamic physical in e ac ions be ween emale
and emb yo. Mo e ecen ly, Kingma (2018, 2019b) has a gued
ha , un il bi h, e uses do no ul ill he adi ional c i e ia
o biological indi iduali y, such as being bounded by opological
on ie s o delinea ed by physiological o immunological
mechanisms. Ins ead, she sugges s ha i is p egnan emales,
inclusi e o hei e uses, ha should beconside ed as indi iduals,
al hough she admi s he posi ion o be compa ible wi h he
possibili y ha e uses a e also indi iduals.
Kingma’s me eological app oach o he me aphysical s a us
o p egnancy illus a es a gene al end in deba es on
“o ganismali y”, which, in ocusing on c i e ia o delinea ing
he spa ial iden i y o o ganisms (i.e., “which so s o pa s
should beincluded wi hin he spa ial bounda ies o indi iduals”),
ha e ended o neglec he p oblem o he diach onic iden i y
o o ganisms (i.e., “which so s o e en s should be included
wi hin he empo al bounda ies o a li e”; DiF isco and Mossio,
2021, p. 177). In con as , he in lamma o y e en s associa ed
wi h implan a ion and bi h p o ide diach onic c i e ia o
he indi idua ion o p egnancy, which, in u n, can
becha ac e ized by he speci ic se ies o de elopmen al e en s
cons i u ing his de elopmen al s age.
In his sense, p egnan emales migh no be bes iewed
as being hemsel es o ganisms, bu a he as de elopmen al
s ages in he li e cycle o ce ain (eu he ian) o ganisms. A e
all, li e cycles o mos plan and animal g oups in ol e
d ama ic de elopmen al ans o ma ions and a ied
ep oduc i e phases (Fusco and Minelli, 2019). Jus like
me amo phosis, p egnancy migh be conside ed as a new
o ganiza ional o m associa ed wi h a new de elopmen al
s age, a he han as a new indi idual. Howe e , we belie e
ha he spa io- empo al c i e ia o physiological indi iduali y
do no exhaus he kind o indi iduali y ha p egnancy b ings
abou . Besides ha , p egnancy needs o be ecognized as a
ep oduc i e indi iduali y which is i educible o ha o
de elopmen al o physiological indi iduali y. Unlike he
TABLE1 | Compa a i e able o concep s o biological indi iduali y and how
hey apply o p egnancy.
En i ies C i e ia o
indi idua ion
Numbe and kinds
o indi iduals in
eu he ian
p egnancy
Physiological O ganisms Sel -main enance
Func ional
in eg a ion
One (Pa -whole)
Two (Con aine
model)
E olu iona y Genes
O ganisms,
Species
Uni s o selec ion Th ee (mo he ’s,
a he ’s, and
emb yo’s genes)
Ecological Ecological ne wo ks In e dependence
Sca olding
One (holobion
app oach)
Two (sca olding
app oach)
His o ical Pheno ypes (body
pa s, de elopmen al
p ocesses,
physiological unc ions)
His o ical
pe sis ence
Non-
exchangeabili y
One ( ep oduc i e
sys em)
Nuño de la Rosa e al. P egnan Females as His o ical Indi iduals
F on ie s in Psychology | www. on ie sin.o g 9 Janua y 2021 | Volume 11 | A icle 572106
physiological sys ems pa icipa ing in o ganismic main enance
(such as he diges i e, ci cula o y o espi a o y sys ems),
ep oduc i e unc ionali ies a e no jus con ibu ions o he
sel - o he sca olded homeos asis o indi idual o ganisms,
bu o a di e en ype o homeos asis, namely he main enance
o p egnancy as a ela ional p ocess ha migh in ol e di e en
physiological indi iduals (Pa liče e  al., 2017; S ad maue
and Wagne , 2020a,b). As a consequence, physiological and
ep oduc i e c i e ia o indi iduali y do no necessa ily ende
he same en i ies, al hough hey migh o e lap a ce ain
s ages o he li e cycle. Thus, emb yos migh be conside ed
o bephysiologically indi idua ed be o e bi h, bu o belong
o he ep oduc i e sys em un il bi h. In his sense, e en
i bi h is seen as an a bi a y e en om he pe spec i e
o he physiological indi iduali y o emb yos, i se s a empo al
limi o ep oduc i e indi iduali y, inso a as i b eaks he
ela ion inaugu a ed by implan a ion and en ails an in eg al
eaccomoda ion o bo h he emale and he emb yo
physiologies.7 I is his new kind o ep oduc i e indi idual,
we claim, ha is indi idua ed in e olu ion, gi ing ise o a
no el his o ical indi idual which includes he whole lineage
o eu he ian p egnan emales.
E olu iona y Indi iduali y
The e olu iona y no ion o indi iduali y se s he mains eam
iew in he philosophy o biology. In he concep ual amewo k
o he Mode n Syn hesis, indi iduals a e unde s ood as
heo e ical en i ies o e olu iona y biology, namely, hose ha
play a ole in he heo y o e olu ion by na u al selec ion,
hei main ea u es being a ia ion, he i abili y, and di e en ial
i ness (God ey-Smi h, 2013). F om his pe spec i e, en i ies
below and abo e he le el o he o ganism, such as genes,
g oups o species, can also wo k as indi iduals unde s ood
as uni s o selec ion.
As wesaw abo e, he con lic hypo hesis is he mains eam
hypo hesis in e olu iona y explana ions o p egnancy. This iew
a ibu es in e es s o he genes (alleles o ma e nal and pa e nal
o igin), which a e “exp essed” h ough hei in e ac o s: mo he s
and emb yos, he la e ac ing as he ehicle o bo h pa e nal
and ma e nal in e es s. Al hough con lic applies o he genes
and no o hei ca ie s, as Haig (2014) himsel has wa ned
abou , unde his model, p egnancy ea u es as a place o
nego ia ion o he p esumed in e es s o sepa a e indi iduals
(namely, he mo he , he a he , and he emb yo), a he han
as a biological sys em on i s own. In con as , ou no ion o
his o ical indi iduali y e eals an impo an con as o his
con en ional e olu iona y concep ualiza ion o p egnancy. While,
om an e olu iona y gene ic pe spec i e (lea ing mi ochond ial
7
I migh be a gued ha bi h is an a bi a y e en om a ep oduc i e
pe spec i e, gi en he ex ended pe iod o neona al imma u i y ha ollows
bi h in some mammals, and hei dependence on lac a ion. In his iew, he
physiological indi iduali y o p egnan emales would g adually disin eg a e
a e bi h by changing he se o ma e nal-o sp ing in e dependencies o o he s,
indi iduali y becoming a ma e o deg ee. While his is a plausible in e p e a ion,
such a posi ion would no be able o indi idua e p egnancy, bu a he he
mo e gene al kind o ela ionship media ing mo he s and o sp ing among
mammals, including o ipa ous mammals.
genes aside), pa e nal and ma e nal oles a e on ologically
equi alen , om a ep oduc i e pe spec i e, hey a e no . The
eason is ha he la e accoun in eg a es in o he p ocess o
ep oduc ion he gene ic, mo phological, de elopmen al, and
physiological p ocesses which a ec ma e ial ep oduc i e
ela ions among li ing sys ems and which esul in he p oduc ion
o a new o ganism wi h a new li e his o y.
None heless, e olu iona y app oaches o indi iduali y a e
no necessa ily commi ed o a gene-cen e ed iew o
ep oduc ion. Unde non- educ ionis app oaches o Da winian
indi iduali y whe e o ganisms, g oups, o e en species can
beconside ed as uni s o selec ion, p egnan emales including
hei o sp ing migh beseen as e olu iona y indi iduals seeking
o maximize i ness. Acco ding o he c i e ia used by Cla ke
(2010) o God ey-Smi h (2013), p egnan emales would no
beconside ed as single e olu iona y indi iduals because mo he
and o sp ing a e gene ically di e en , e en hough hey ha e
pa ially o e lapping i ness in e es s. None heless, Kingma
(2019b) seems o each he opposi e conclusion when she
analyzes he indi iduali y o p egnancy om an e olu iona y
pe spec i e. In his case, i migh bea gued ha ou p oposed
no ion o his o ical indi idual and ha o e olu iona y indi iduals
o e lap o he case o p egnancy, hus ende ing ou s supe luous.
Howe e , we belie e ha he i ues o iden i ying new kinds
o biological indi iduals do no lie in hei dis inc i e delinea ing
capaci ies, bu a he in hei abili ies o explain phenomena
ha o he no ions o indi iduali y a e unable o explain (DiF isco,
2019). T acking he p egnan emale as a his o ical indi idual
accoun s o he de elopmen al basis ha explains he bounda ies
and pe sis ence o p egnancy, he dis inc e ol abili y o his
ep oduc i e sys em, and he associa ed changes ha ake place
in he eu he ian lineage a e he eme gence o p egnancy.
None o hese phenomena belongs o he explananda o
selec ionis explana ions o p egnancy as a ep oduc i e s a egy.
Ecological Indi iduali y
An impo an con ibu ion o he deba e on biological
indi iduali y has su aced in he las decade ou o he g ea e
a en ion paid o how ela ions o o ganisms wi h he bio ic
and abio ic milieu challenge some o ou ecei ed assump ions
on indi iduali y. While he ecological no ion o indi iduali y
(Huneman, 2014) can be applied o composi es including
nonli ing pa s, i has been pa icula ly in luen ial in discussions
on he s a us o mul i-species pa ne ships (Quelle and
S assmann, 2016; He nández and Vecchi, 2019), and mo e
speci ically o symbio ic associa ions (Gilbe e al., 2012; Gilbe
and Taube , 2016). So-called “holobion s” challenge he iew
o indi iduals as non-p oblema ic well-bounded en i ies, some
claiming ha ce ain symbio ic associa ions can beunde s ood
as collec i e indi iduals (Chiu and Gilbe , 2015) o as “hyb ids”
made o indi iduals o di e en lineages (Chiu and Ebe l, 2016).
Impo an ly, ecological e lec ions on he s a us o symbion s
do no necessa ily a emp o eplace he physiological and
e olu iona y c i e ia o indi iduali y. Ra he , symbion s migh
beindi idua ed di e en ly depending on he adop ed pe spec i e.
Thus, some conside holobion s as uni s o selec ion
(Roughga den e  al., 2018), while o he s admi ha some