The Status of Homo heidelbergensis

The Status of Homo heidelbergensis(Schoetensack 1908)Chris Stringer

The species Homo heidelbergensis is central to many discussions aboutrecent human evolution. For some workers, it was the last common ancestor forthe subsequent species Homo sapiens and Homo neanderthalensis; othersregard it as only a European form, giving rise to the Neanderthals. Following theimpact of recent genomic studies indicating hybridization between modernhumans and both Neanderthals and Denisovans, the status of these as sepa-rate taxa is now under discussion. Accordingly, clarifying the status of Homoheidelbergensis is fundamental to the debate about modern human origins.

THE SPECIES HOMOHEIDELBERGENSIS

In 1907, the robustly built mandi-ble that was to become the holotypeof Homo heidelbergensis was discov-ered in the Grafenrain sandpit atMauer, near Heidelberg, Germany,associated with what is now termeda Galerian or Cromerian (early Mid-dle Pleistocene) fauna. The speciesname was bestowed a year later byOtto Schoetensack,1 who noted inthe Mauer mandible the combinationof primitive features (for example,high corpus thickness, very wideramus, and receding symphysis) andmore recent human features, such assmall dentition, particularly the can-ines and anterior teeth. The name

was little used during the earlier partof the twentieth century and, by the1960s the lumping together of taxaoften treated the fossil as a Europeanform of Homo erectus.2 However,Howell3 took exception to that, argu-ing that the fossil probably was mor-phologically distinct enough to repre-sent a separate species.

In 1974, I completed my doctoralthesis, which concentrated on cranialshape comparisons of Neanderthaland modern humans but, along theway, I noted clear phenetic resem-blances between the Broken Hill(Zambia) and Petralona (Greece) fos-sils, and considered both of these tobe clearly distinct from Neander-thals.4,5 Rather than allocate eitherof these specimens to Homo erectus,I preferred, at that time, to regardthem as related primitive forms ofHomo sapiens sensu lato, eventuallyassigning them to Homo sapiensgrade 1 in a gradistic scheme.6

Following discussions with BjornKurten, I became aware of biostrati-graphic evidence that elements of thePetralona mammalian faunas wereof Cromerian age, potentially compa-rable to those from Mauer.7 BothKurten and I considered the possibil-ity that the Petralona cranium couldrepresent a counterpart for theMauer mandible,6,8 even though the

two clearly do not articulate well. Inthe early 1980s, with a shift to cladis-tic thinking and influences, I beganto gravitate toward the idea thatNeanderthals were, after all, a dis-tinct species from Homo sapienssensu stricto, and that this impliedthe existence of a distinct ancestralspecies, if neanderthalensis and sapi-ens were sister taxa, and erectus didnot represent the last commonancestor. Through linking Mauerwith Petralona and Petralona withBroken Hill, the concept of a Eura-frican stem species named Homo hei-delbergensis began to develop.9 Thefollowing extract and accompanyingfigure (Fig. 1) summarize the cau-tious arguments made at that time:Because at present they cannot bedefined satisfactorily by their owndistinctive within-group characteris-tics, it is difficult to justify creating aseparate taxon for the Petralona andBroken Hill fossils on the basis ofcharacters they lack, or ones theyshare with other taxa. Nevertheless,given the need to recognize theirsimilarities to each other, and toother Middle Pleistocene fossils, theycould be placed in a separate species,H. rhodesiensis or H. heidelbergensis(if the Mauer mandible is alsoincluded), provided the distinctive-ness of the Neanderthals frommodern H. sapiens is also consid-ered worthy of specific recognition(Fig. 1a). Alternatively their possibleposition as a stem group for theUpper Pleistocene hominids could berecognized by the use of a subspe-cific name for the evolutionary gradethey are supposed to representwithin H. sapiens (Fig. 1b). However,the other possibility that mustbe considered (Fig. 1c) is that we

ISSUES

Chris Stringer has worked at The NaturalHistory Museum London since 1973, andis now Research Leader in Human Ori-gins and a Fellow of the Royal Society.He has excavated at sites in Britain andabroad, and is currently leading theAncient Human Occupation of Britainproject. Email: [email protected]

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VVC 2012 Wiley Periodicals, Inc.DOI 10.1002/evan.21311Published online in Wiley Online Library(wileyonlinelibrary.com).

Evolutionary Anthropology 21:101107 (2012)

cannot at present resolve the exact

phylogenetic position of these homi-

nids because they are close to the

point of divergence between Nean-

derthals and modern H. sapiens(assuming that the Neanderthals are

not directly ancestral to modern

humans). At present I believe this to

be quite likely, and that these fossils

are close to the morphotype expected

in the common ancestor of Neander-

thals and modern H. sapiens. If thisis so, only further careful analysis

will allow a decision about the clad-

istic affinities, and thus the classifica-

tion, of fossils such as Arago 21, Pet-

ralona and Broken Hill.I began to develop a suite of traits

(Table 1; Fig. 2) for grouping BrokenHill and Petralona.10 European andAfrican fossils such as Bilzingsleben,Vertesszollos, Bodo 1, and Elands-fontein were added to an enlarged

heidelbergensis hypodigm. A separatestudy of the first Bilzingsleben cra-nial finds reinforced their resem-

blance to the Elandsfontein calva-ria,11 and the possibility that Middle

Pleistocene Chinese and Indian fos-

sils might also belong in this group

(Table 2) was raised.12,13 Rightmire

has adopted a comparable Eurafri-

can concept of heidelbergensis,14,15

while some have preferred to retain

a more gradistic concept of Homosapiens, arguing that fossils such asBroken Hill and Bodo are primitive

examples of the modern human spe-

cies.16 Other workers have used the

informal term ante- or preneander-

thal for earlier European fossils,

including Mauer and Arago, some-

times with a purely chronological

meaning, and in other cases imply-

ing an evolutionary relationship.17

This latter option has becomeincreasingly popular with the recog-nition that the Sima de los Huesos(SH) material displays a mosaic ofheidelbergensis and neanderthalensisfeatures. For such workers, H. heidel-bergensis could represent an earlystage in the accretion model of Ne-anderthal evolution,17,18,35 forming aheidelbergensis-neanderthalensis con-tinuum. I briefly considered thisargument, going so far as to suggestthat all heidelbergensis materialmight be lumped into Homo neander-thalensis,19 but I did not persist inthat view. However, if the European-only model of heidelbergensis iscorrect, then the non-European com-ponents assigned to heidelbergensisby workers such as Rightmire and

Figure 1. Illustration of the possible phylogenetic relationships of the Petralona and BrokenHill fossils. Redrawn, with permission, from Stringer.9

TABLE 1. Some Traits Observed in H. heidelbergensis FossilsEndocranial volumes overlap those of H. erectus and H. sapiens/H.neanderthalensis

Torus often highly pneumatized laterally, and superiorly into frontal squamaVault shape parallel-sided in posterior viewStrong and continuous supraorbital torus*Occipital bone strongly angled*Strong continuous occipital torus*Wide interorbital breadth*Iliac pillar*Elongated superior pubic ramus*#Femoral platymeria*#High arched temporal squama1#Gracile tympanic1#Increased midfacial projection expressed through measures of midline nasal

prominence1#In large-faced specimens there may be lack of both canine fossa and

infraorbital retraction#Reduced total facial prognathism1#

*Found in Homo erectus; potential synapomorphies with H. sapiens; # potentialsynapomorphies with H. neanderthalensis.

102 Stringer ISSUES

me, which show few or no Neander-thal apomorphies, would require aseparate species names. Homo rhode-siensis 20 would have priority for thatgrouping.9,21

RECENT RESEARCH ON THEMAUER MANDIBLE, AND THE

SPECIES HYPODIGM

Recently, welcome attention hasbeen given to the Mauer mandibleitself, including further datingwork.22 Schwartz and Tattersall23

compared its morphology with thatof other Pleistocene hominins, notingits particular resemblance to theArago 13 mandible. Via the Aragoassemblage, they were able to extendtheir heidelbergensis grouping toother European, Chinese, and Afri-can fossils, while aligning the SHmaterial with Neanderthals. How-ever, in their view, the derivednatures of both the Neanderthalclade and Homo heidelbergensisexclude these groups from the ances-try of Homo sapiens.

Rak and colleagues41 noted the idi-osyncratic features of the Mauer jawand argued that it is not clearwhether lumping certain specimenstogether in this hypodigm is justified

at all. In effect, the morphology ofcertain specimens does not accordwith that of the type specimen. Obvi-ously, the taxonomic identification ofskulls lacking a mandible is problem-atic, but even some mandibles giverise to uncertainty regarding theirassignment to the H. heidelbergensishypodigm. In our analysis, theMauer mandible stands alone in itsmorphology, which appears to be theoutcome of a unique constellation ofcharacters. This mirrored the viewof Hublin,21 who argued that theprimitive nature of the Mauer man-dible and the predominance of cra-nial material in discussions aboutMiddle Pleistocene hominins ren-dered it unsuitable as a holotype.

In the most extensive comparativeanalysis to date, Mounier, Marchal,and Condemi24 concluded that theMauer mandible and H. heidelbergen-sis could be specifically distinguishedfrom H. erectus, H. neanderthalensis,and H. sapiens. They produced a di-agnosis for the species hypodigmbased on mandibular fossils suchMauer, Arago, Montmaurin, and SH.Their inclusion of the Tighenif man-dibles extended the species to Africa,but unfortunately they did notinclude other potential African exam-

ples of heidelbergensis, such asThomas Quarry and Kapthurin, in

TABLE 2. Some Fossils That MayRepresent Homo heidelbergensis*

Western EurasiaMauerPetralonaAragoVertesszollos?Bilzingsleben?Kocabas?Boxgrove?Ceprano?Zuttiyeh

AfricaBroken Hill 1; tibia E.691; pelvis E.719BodoElandsfonteinNdutuKapthurin?Hoedjies punt?Thomas Quarry?Sale?Tighenif?Berg Aukas

Eastern Eurasia?Narmada?Dali?Jinniushan?Yunxian

*In my view, the inclusion of fossils such asSteinheim and Montmaurin is still doubtful,while Narmada, Dali and Jinniushan mayalternatively represent early Denisovans.

Figure 2. Facial (A) and lateral (B) views of crania. Clockwise from top left: Homo erectus (replica, Sangiran, Java), heidelbergensis (Broken Hill,Zambia), sapiens (recent, Indonesia), and neanderthalensis (replica, La Ferrassie, France). All pictures The Natural Histroy Museum London.[Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

ISSUES The Status of Homo heidelbergensis 103

their analyses. However, it is worthremembering that a fragment oframus found at Elandsfontein, possi-bly associated with the Saldanha cal-varia, was noted as being remarkablysimilar to that of Mauer in its shape.25

As mentioned, researchers usingmetric and multivariate techniqueshave noted metrical and shape simi-larities between Petralona and Bro-ken Hill.5,14,26 This has been con-firmed through the use of geometricmorphometrics.27,28 For example,Friess,28 excluding the Mauer mandi-ble, commented that the strikingaffinities between the holotype of H.rhodesiensis (Kabwe) and a Euro-pean fossil (Petralona), as demon-strated previously and confirmedhere, are unlikely to disappear, evenif more complete specimens were tobe included in the analysis. Thismakes H. rhodesiensis an Afro-Euro-pean species that retains an erectus-like plesiomorphic calvarial shape,but no Neandertal/H. sapiens apo-morphies, unless one lumps it withSH5 and Steinheim. In a furtherstudy, Mounier, Condemni, andManzi29 added the Ceprano calvariato their comparative analyses. Theygrouped the Ceprano specimen withEurasian fossils such as Petralona,SH5, Steinheim, Dali, and Jin-niushan, as well as with the BrokenHill cranium. They concluded that inspite of its relatively young chrono-logical age (385-430 ka), the Cepranofossil could represent a morphologi-cally primitive example of the widelydispersed species heidelbergensis.

ARE THE SIMA DE LOS HUESOSFOSSILS PART OFHEIDELBERGENSIS?

Although Mounier and co-workers24,29 felt able to include theSH material in their heidelbergensishypodigm, I believe that this inclu-sion has led to the most serious con-fusion surrounding the status of thespecies. From the first detaileddescriptions of the Sima fossils, theircombination of heidelbergensis-likeand Neanderthal-like features hasbeen recognized.19 Increasingly oldage estimates for the SH assemblage(now >530 ka30,31) have reinforced

the Atapuerca teams preference forassigning the material to heidelbergen-sis. However, for some time I havepreferred to regard the SH materialas an archaic form of neanderthalen-sis,13 based on the presence of Nean-derthal-like features such as an incipi-ent suprainiac fossa and midfacialprojection in the crania, dental andmandibular traits, and numerouspostcranial characters. More recently,I have also challenged the older ageestimates obtained for the SH samplefrom a dated speleothem.32 That chal-lenge was based on taphonomicissues rather than the age determina-tion itself, but dating work on thespeleothem is continuing (J.-L.Arsuaga, personal communication).

Regardless of those considerations,morphological and genetic data sug-

gest that the divergence of the nean-derthalensis and sapiens lineages verylikely postdates 530 ka. Therefore,Neanderthal apomorphies would notbe expected at such an antiquity.Comparisons using the draft Nean-derthal genome produced the follow-ing estimate: Assuming that human-chimpanzee average DNA sequencedivergence was 5.6 to 8.3 millionyears ago, this suggests that Nean-dertals and present-day human pop-ulations separated between 270,000and 440,000 years ago.33 Using onlycomplete mtDNA sequences, Endi-cott, Ho, and Stringer32 argued thatour genetic date estimates areinconsistent with the late Early Pleis-tocene, early Middle Pleistocene, andlate Middle Pleistocene models forthe divergence between H. sapiensand H. neanderthalensis.... Rejectionof these three models leaves just themid-Middle Pleistocene model forthe time of divergence between mod-

ern humans and Neanderthals. . ..Here, our 95% credible intervals forthe MRCA [most recent commonancestor] (315-538 ka) fall squarelywithin the proposed dates frompalaeoanthropology.... Our estimatesare also consistent with dates derivedfrom analysis of neutral morphologi-cal characters in both species, 182-592 ka (mean 373 ka).34

Recently, even stronger reasonshave emerged to place the SH mate-rial within the Neanderthal claderather than within heidelbergensis.Data from the large SH dental sam-ple have long suggested Neanderthalaffinities.35 Most recently, Martinon-Torres and colleagues36 concluded:We find that SH dentitions presentall the morphological traits that, ei-ther in their degree of expression,frequency, or particular combina-tion, are usually considered as typi-cal of Homo neanderthalensis. Thisstudy ratifies the deep roots of theNeanderthal lineage in the MiddlePleistocene of Europe. In addition,SH teeth are morphologically moreNeanderthal than other penecontem-poraneous Middle Pleistocene sam-ples such as Mauer or Arago, andeven more derived than some classicNeanderthal samples. Because theyadhere to an age of >530 ka for theSH sample, these authors are forcedto add, Thus, our study would notsustain the linearity of the accretionprocess hypothesized for the originsof the Neanderthals, and we suggestthat other evolutionary models andscenarios should be explored for theMiddle and Upper Pleistocene ofEurope. We propose that more thanone hominin lineage may have coex-isted during the Middle Pleistocenein Europe. While I agree with thatlast statement, it is on completelydifferent grounds. Martinon-Torresand coworkers35 argue for this onthe basis of an (in my view errone-ous) early date for neanderthalensis(SH) characteristics. I would insteadargue for coexistence on the basis oflate heidelbergensis age estimateswithin and outside of Europe.29,3740

In addition, it may well be that sig-nificant Neanderthal-like samplessuch as Krapina, considered to berelatively late in the Europeansequence, are older than is currently

Recently, even strongerreasons have emergedto place the SH materialwithin the Neanderthalclade rather than withinheidelbergensis.

104 Stringer ISSUES

believed (R. Grun and C. Stringer,unpublished research).

Rak and coworkers41 have recentlyadded to the data that the SH materialis predominantly Neanderthal in itsaffinities: The claimed similaritiesbetween the characters of the Mauerspecimen. . .and those of Neandertalsand the Sima de los Huesos mandi-bles. . .cannot be considered homolo-gous, and hence, they are not synapo-morphies. Although some of theMauer characters superficially resem-ble the ones on the Neandertal andSima specimens, the Mauer charactersstem from a different morphologicalconfiguration. On the other hand, thesimilarities between the Neandertalcharacters and those of the Sima man-dibles are the outcome of identicalconfigurations, making these charac-ters true synapomorphies. This wasreinforced as follows: The study ofmandibles from Sima de los Huesosreveals an identical morphology tothat of the corresponding and uniqueregion in the Homo neanderthalensismandible.... This constellation of char-acters is absent in other early and latehominins, including the type specimenHomo heidelbergensis (the Mauer man-dible).... We conclude that the mandi-bles of the Sima sample are virtuallyidentical to the Neandertal mandible.Thus, we regard this morphology as asynapomorphy that the Sima fossilsshare only with H. neanderthalensis. Insome other cranial morphologies, theSima sample does not resemble Nean-dertals; hence, we place the Simaspecimens within the Neandertal cladeas a sister group to Neandertals. Thisconclusion is inevitable regardless ofwhether one advocates a cladogeneticor anagenetic model.42

GENOMIC DATA AND THE STATUSOF HEIDELBERGENSIS

As I previously argued,32 reclassify-ing the SH material as an early formof H. neanderthalensis on the basis ofits derived Neanderthal features anddating it to no earlier than 400 kawould remove most of the data sup-porting a European chronospecies ofH. heidelbergensis-H. neanderthalensis.This would open the possibility of aless inclusive diagnosis for the species

that is ancestral to modern humansand Neanderthals, which, in my view,is still most reasonably named Homoheidelbergensis. However, new data onthe possible eastern representatives ofheidelbergensis have emerged from thegenomic study of fragmentary fossilsat the southern Siberian site of Deni-sova. Initial mitochondrial DNA(mtDNA) study of a large molar sug-gested an ancient lineage predatingthe divergence of Neanderthals andmodern humans, but genomic recon-struction centered on a phalanx indi-cated that the Denisovans wereactually a subgroup of the Neander-thal clade.47 This finding has fueledspeculation that fossils previouslyconsidered to be possible Asian repre-sentatives of heidelbergensis, such asDali, Jinniushan, and Narmada,13

could in fact be Denisovans, but thiswill remain uncertain until more com-plete material yields DNA. More an-cient Asian specimens such as theYunxian crania (China) might stillrepresent examples of heidelbergen-sis13,43 and potential ancestors of theDenisovans, although biogeographicand archeological arguments can bemade against such as assignment.44

In addition, the presence of relativesof the Neanderthals in the Far Eastforcefully reminds us how much ourviews are biased by the attention paidto the European and African records.We cannot exclude an Asian origin forheidelbergensis, given the similar ages(600 ka) assigned to the earliest (ifwe exclude Tighenif) potential exam-ples in Germany (Mauer22), China(Yunxian45), and Ethiopia (Bodo46).

The new Denisovan genomic dataare also consistent with previous evi-dence of gene flow between Homosapiens dispersing from Africa andnative archaic populations (Neander-thals).33 Limited but viable hybrid-ization events led to an input of ar-chaic genes into all non-Africanpeople in the case of NeanderthalDNA, and Australasian populationsin the case of the Denisovans.47 Suchgene flow is bound to raise seriousissues about the validity of specificdistinctions between heidelbergensisand its daughter species, particularlyas such hybridization events mayeven have occurred in Africa.48,58

Nevertheless, on morphological

grounds, I believe that a pragmaticcase can still be made for such spe-cies distinctions, especially bearingin mind the extensive evidence forinterspecific hybridization even inliving primates.49

Genetic data can provide new per-spectives on the evolutionary historyof heidelbergensis and its daughter spe-cies, as can be illustrated by compar-ing Figure 1c and Figure 3, based onthe mtDNA divergence data discussedearlier. Gene trees are not speciestrees, of course, but Figure 3 maynonetheless serve as a useful heuristicdevice. First, it is evident that both themodern human (A) and late Neander-thal lineages (B) may have sufferedbottlenecking, perhaps during theharsh conditions of Marine IsotopeStage (MIS) 6; the slender evidence ofDenisovan mtDNA already suggestsgreater diversity in that lineage.50

Genetic diversity that would have beenrepresented within early or archaicmembers of the sapiens (C) and nean-derthalensis groups (D) has conse-quently been lost. The hypotheticalmtDNA last common ancestor forAC and BD is estimated at 338-538ka (mean 407 ka), while populationdivergence is placed at 315-506 ka(mean 345 ka). The predivergence seg-ment labeled F would have existedduring the time span of Homo heidel-bergensis. I argue that if we had fossilsof the relevant ancestors, we wouldrecognize them as members of thatspecies. While fossils such as Swan-scombe and SH might correspondwith segments D or E, in my view wehave yet to identify specimens showingconvincing apomorphies of Homosapiens that could represent the ear-liest stages of segment C, although fos-sils such as those from Florisbad andGuomde are possible candidates.

As for what initiated the divergenceof these lineages, one possibility is toreturn to an idea suggested more than50 years ago by Howell,51,52 thoughframed by him in the context of thelast glaciations. There is evidence nowthat glaciation in the Balkans wasmuch more severe during the MiddlePleistocene than at the Last GlacialMaximum.53 Also, pollen data fromTenaghi Philippon indicate that MIS12 (450 ka) was particularly severe.54If, at that time, cold, arid conditions


extended eastward across the highrelief of the Taurus-Zagros mountainsystems, coupled with enlarged Cas-pian and Black Seas, European popu-lations could have been effectively iso-lated from their African and Asiancounterparts. Moreover, increasedaridity in North Africa and the Levantcould have added to this paleogeo-graphic separation. Whether increasedselection or drift then operated to dif-ferentiate these separated populationsprogressively is still uncertain,55

but Neanderthal-derived features areevident in Europe from MIS 11onward.13,52,56

A comparable speciation scenario,using the mechanisms of refugia, hasrecently been proposed by Stewartand Stringer57: When a lineageadopts a new (or changes its) refu-gial area, and it survives for a num-ber of Milankovitch cycles, expand-ing from and contracting into thatnew refugium instead of its originalrefugium, it is destined to evolve intoa distinct population. Given enoughtime in isolation, it will become anew species. . .. A new refugium isunlikely to have the same flora,fauna, and ecology compared to thelineages original refugium, which

contributes selective pressure toadapt and diverge.

CONCLUDING REMARKS

Clearly, many problems in MiddlePleistocene human evolution remainunresolved. Some of these center onchronological issues, others on thelack of data for some important fossils,such as those from China. The rela-tionship of Homo antecessor, still defi-nitely identified only from Atapuerca,to succeeding samples is also unclear,although it remains possible that thisderivative of Homo erectus wentextinct during the early Middle Pleisto-cene.59 Homo antecessor also seems anunlikely ancestor for Homo heidelber-gensis, which means that the origin ofHomo heidelbergensis is obscure. How-ever, in my view, the main uncertaintyabout Homo heidelbergensis is muchmore fundamental, concerned with itsvery nature. The idiosyncratic mor-phology of the type specimen is cer-tainly problematic, but for me an evenmore vexing issue is whether the spe-cies existed only in western Eurasiaand gave rise solely to the Neander-thals. The main support for such aview has come from the derived Nean-

derthal features claimed for the spe-cies, simultaneously differentiating itfrom contemporaneous African fossilsand linking it to the succeeding Nean-derthals.

In this review, I have discussed thegrowing and, in my view, convincingevidence that the Sima de los Huesosmaterial belongs to the Neanderthalclade, and perhaps represents aprimitive form of Homo neandertha-lensis. Removing the extensive SHassemblage from H. heidelbergensisgreatly clarifies the situation in alsoremoving most of the unique links tothe Neanderthals. This allows areformulated heidelbergensis to ap-proximate more closely the plesio-morphous morphotype expected forthe last common ancestor of Homoneanderthalensis and Homo sapiens.However, if genetic and morphologi-cal estimates for neanderthalensis-sapiens divergence at

permission from Elsevier. The originalversion of Figure 3 was kindly suppliedby Phillip Endicott. My work formspart of the Ancient Human Occupa-tion of Britain project, funded by theLeverhulme Trust, and is supported bythe Human Origins Research Fund,and the Calleva Foundation.

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