Ten years. That’s how long it takes for the modern human brain – that of Homo

sapiens – to reach maximum performance. But this was not always the case:

the offspring of Homo erectus, who lived approximately two million years ago,

had almost adult-sized brains just a year after birth. Director JEAN-JACQUES

HUBLIN and his team of researchers at the MAX PLANCK INSTITUTE FOR

EVOLUTIONARY ANTHROPOLOGY in Leipzig have been looking into the facts.

What Our AncestorsHad in Their Heads

56 M A X P L A N C K R E S E A R C H 1 / 2 0 0 5

FASCINATING Research

1 / 2 0 0 5 M A X P L A N C K R E S E A R C H 57

Evolutionary ANTHROPOLOGY

Compared with all other pri-mates, human beings exhibit

one particularity: their offspring gothrough a distinct infancy and child-hood. This phenomenon is still rela-tively new in the history of mankind.That is the conclusion reached by theteam working with Jean-JacquesHublin and Hélène Coqueugniot(University of Bordeaux 1) in an ar-ticle published by the British journalNATURE (September 16, 2004). Thescientists examined an approximate-ly 1.8-million-year-old skull, the on-ly known example from a child ofour direct ancestor, Homo erectus.The skull of the “Mojokerto child”was discovered in the Mojokerto re-gion of Java in 1936 by an excava-tion team led by German anthropol-ogist Gustav Heinrich Ralph vonKoenigswald. The completely pre-served skullcap is particularly wellsuited to scientific examination.

Changes in bodily maturationthroughout human evolution aredocumented by analysis of dentalmaterial. The growth patterns andlong adolescent phase typical for

modern Homo sapiens emerged rela-tively late in human developmentalhistory. Based on the growth patternof the teeth of Homo erectus, it canbe assumed that the maturation pro-cess was faster than that of today’shumans. The question regarding thebrain growth of Homo erectus, how-ever, has remained unanswered. Didhis brain mature after birth for aslong as Homo sapiens’ did?

To date, the question of when,during the approximately six-mil-lion-year-long evolution of humans,the protracted post-natal braingrowth – the “secondary altriciality”– emerged has been disputed. Fos-silized human skulls, especially thoseof children, are very rare. The Mo-jokerto skull has brought new in-sights: with the help of computer to-mography (CT), Hublin and his teamwere able to examine this find rightdown to the tiniest detail. Virtual paleoanthropology calls this the“touchless” method, which differsfrom earlier procedures in that itdoes not damage the fossils in anyway. “Computer tomography facili-tates our work considerably, sincethe Mojokerto skull is completelyfilled with sediment,” explains Jean-Jacques Hublin. “Thanks to the CTdata, we were able to clearly distin-guish the sediment from the bone re-mains and could thereby preciselydetermine the brain volume.”

Hublin describes this method ofseparating rock and bone material as“virtual cleaning.” For this, the Mo-jokerto skull was scanned by com-

Only rarely does Jean-Jacques Hublin hold the objects of his research in his hands (photoopposite). For the most part, fossilized human bones are analyzed through computer tomography without handling them - above, an image of the scanned Mojokerto skull.

PHO

TOS:

TH

ORS

TEN

NAE

SER/

MPI

FO

REV

OLU

TIO

NAR

YAN

THRO

POLO

GY;

NAT

URE

431,

299

-302

(SEP

TEM

BER

16, 2

004)

/SEN

CKEN

BERG

MU

SEU

M

Computer tomography (CT) supplements conventional photo techniques: Left, the Mojokerto child's skull from above; right, spatial CT views in which the bone material appears smooth and sediment is betrayed by its grainy structure.

1 / 2 0 0 5 M A X P L A N C K R E S E A R C H 59

Evolutionary ANTHROPOLOGY

puter tomography in single layers.“Computer tomography scatters X-rays differently on skull particles androck,” says Jean-Jacques Hublin.“This enables the rock to be removedin the same manner.” After virtually“cleaning” the individual images inthis way, the researchers superim-posed them, deriving a completethree-dimensional image of the skull.

Further analysis revealed that thechild was most likely no more thanone year old at the time of death –contrary to previous estimates thathad put the death of the Mojokertochild at between the ages of four andsix. The new estimation of the age atdeath resulted from the analysis ofthe state of ossification of differentskull parts: the Pars tympanica, oneof the bone plates at the front of theauditory canal, the anteriorfontanella in the bregma, and thesubarcuate fossa, a cavity in the re-gion of the petrosal bone, whichcloses during childhood. Finally, thescientists compared this data withmodern human skulls of 159 chil-dren between the ages of 0 and 8,and with 201 skulls of young chim-panzees and bonobos.

In doing so, it became apparentthat the tympanic part of the Mo-jokerto child was completely ossi-fied. On the other hand, the bregmaand the subarcuate fossa were not

fully developed. Furthermore, theexamination of the bregma showedthat spongiosa, a porous substancebetween the two cranial plates, hadonly started to accumulate. Howev-er, the os parietale were not fullyformed; there was still a gap of 3.5millimeters between them that sug-gested a partly closed anteriorfontanelle or even post-mortal dam-age. A further criterion for age de-termination was provided by the de-gree of subarcuate fossa closure.Comparison with correspondingfinds in young modern human be-ings and young chimpanzeesshowed that the Mojokerto childmust have been about a year old atthe time of death.

COMPARISON

SHEDS LIGHT

Computer tomography provided yetanother surprise: the infant alreadyhad an endocranial capacity of be-tween 70 and 84 percent of thatfound in various samples of Homoerectus. In a second step, the re-

searchers compared the Mojokertoskull – which encompassed a brainvolume of 663 cubic centimeters –with the skulls of present-day pri-mates. The result: post-natal braingrowth of the Homo erectus childwas more similar to that of chim-panzees than to that observed in ex-tant humans. “The data indicatesthat the time during which the brainof the Homo erectus child could ma-ture after birth was very short,” saysJean-Jacques Hublin.

Significant differences became ap-parent in a comparison with modernhumans, who are born relatively im-mature: at birth, they possess onlyabout 25 percent of their later brainvolume of approximately 1,350 cu-bic centimeters. During the first yearof life, their brain grows at the samespeed as before birth and reachesabout 50 percent of its ultimate vol-ume after one year. Modern man’sbrain is full-grown only after thetenth year. This means that it ma-tures more slowly and for a longerperiod than all other primates.

“This maturation period, or sec-ondary altriciality, gives Homo sapi-ens significant advantages comparedto his earlier relatives,” explainsHublin, referring to the developmentof cognitive abilities of children dur-ing the first ten years. “During thistime, the young brain is exposed toinnumerable environmental stimuli.That gives rise to intense interplaybetween the somatic and sensomo-toric regions of the brain.”

However, it’s unlikely that sec-ondary altriciality was initially select-ed for this reason. A small, still im-mature brain at birth gives mothers adecisive advantage during child-rear-ing. Homo sapiens require largeamounts of energy to maintain brainfunctions. A human adult uses about20 percent of his energy for thinkingand to keep his brain at “operatingtemperature.” Hublin explains, “In thecase of an inter-utero embryo it iseven 50 percent. Therefore, in aspecies with very large brains, it iseasier for mothers to provide theirchildren with this large amount ofenergy after birth in the form of food,rather than providing it with theirown body during pregnancy.”

And there is a physiological ad-vantage for women. Since the headsof their babies haven’t reached theirfinal volume at birth, even motherswith a narrow pelvis can give birth.According to Hublin, “A narrowerpelvis increases a woman’s mobilitysignificantly. This was important intimes when people moved about agreat deal.” Secondary altricialitymust also have played an importantrole in the development of language.The Leipzig scientist is convincedthat Homo erectus already possessedcommunicative abilities; however,the generally smaller brain volumeand the lack of secondary altricialitymust have severely limited the cog-

MAN – A GLOBAL PUZZLE

The reconstruction of human phyloge-netics is like a universal puzzle. The fos-silized skeletal remains are often incom-plete or unique, as in the case of theskull of the Indonesian Mojokerto child.With every new find and improved scien-tific examination methods, paleoanthro-pologists gain a clearer picture of humandevelopment.

There is no doubt as to the close rela-tionship between humans and recent pri-

mates, such as chimpanzees, gorillas and orangutans. Theresults of DNA analysis clearly show this: the genetic ma-terial of humans and chimpanzees differ by only 1.6 per-cent (gorilla: 2.3 percent, orangutan: 3.6 percent). Man’searliest ancestor is considered today to be approximatelysix million years old. It is represented by fossil homininssuch as Sahelanthropus tchadensis and Orrorin tugenen-sis, the “Millennium Man” from the Rift Valley in Kenya.The inner composition of his femur neck bone shows himto be a biped; the bone fossil was found in 2000 in aneastern African rift valley that has long been consideredthe cradle of humanity.

Prior to the discovery of “Millennium Man,” the approxi-mately four-million-year-old bone finds from Kenya andthe four-and-a-half-million-year-old skeleton fromEthiopia were considered the earliest traces of our ances-tors. The first fossils to be described as Homo (human)are nearly 2.4 million years old; they originate from east-ern and southern Africa and belong to Homo habilis. Almost 1.9 million years ago, an advanced human typedeveloped: Homo erectus had a larger brain and a skele-ton similar to that of humans today. Homo erectusspread widely, making his way from Africa all the way tothe Caucasus and to eastern and southern Asia and even-tually, one half to one million years ago, to Europe.

The researchers believe that two different lines of thespecies Homo developed about 500,000 years ago: one as Neanderthal man (Homo neanderthalensis) and one asmodern man (Homo sapiens). Recent studies suggest thatNeanderthal man belonged to a separate species of hu-mans that is now extinct. He was named after the Nean-derthal from Mettmann (between Düsseldorf and Wup-pertal), where a skull of this prehistoric man was firstfound in 1856. The classic Neanderthal lived during themiddle paleolithic – from approximately 130,000 BC to30,000 BC; Neanderthals were more thickset andstronger than today’s humans.

Modern man probably developed from an African line ofHomo erectus. The earliest remains to have been foundare between 100,000 and 120,000 years old. As early as40,000 years ago, Homo sapiens lived in widely separatedregions of Asia and Europe. All living humans ultimatelyemerged from this differentiation.

58 M A X P L A N C K R E S E A R C H 1 / 2 0 0 5

FASCINATING Research

THE ANDOYO FIND

The skull of the Mojokerto child was found in 1936 by Andoyo,an employee of the Dutch Geological Service. At that time, Gus-tav Heinrich Ralph von Koenigswald was also working at the Ge-ological Service. His assignment was to identify fossilized mam-mals, describe them, and compile a classification of the Pleis-tocene based thereon. He only first received the skull in Bandung(West Java). The identification and description were part of hisfield of work. Koenigswald remained in Java from 1930 to 1946, but was imprisoned twice: by theDutch for several months following the German invasion of Holland, and following the Japaneseoccupation of Java. Koenigswald died on July 10, 1982 at the age of 80.

Quicker to the finish: While modern man’s brain is still not fully grown eveneight years after birth, the brain of the Mojokerto child (Homo erectus) was almostcompletely developed after just one and a half years.

Different developmental stages of the subarcuate fossa – a large rounded cavity in the region of the petrosal bone – in modern humans, 2 months (left) and 18 months afterbirth (right). In the center, the same region in the 18-month-old Mojokerto child.

nitive abilities of early man andmade complex language and under-standing impossible. “We can as-sume that complex language, par-allel to secondary altriciality, did not develop until relatively late inhuman evolution,” believes Jean-Jacques Hublin.

With their study, the Max Planckresearchers were able to further narrow down the time period inwhich the typically human charac-teristic of secondary altriciality wasdeveloped. “The immediate predeces-sors of Homo sapiens and Homo neanderthalensis already possessedrelatively large brains,” says Hublin.“Consequently, the lengthy brainmaturation must have developedwithin the timeframe between1,000,000 and 500,000 years ago.”

THORSTEN NAESER

A simplified genealogy of man. Neanderthalman died out 30,000 years ago, and Homo sapiens took over the continents.

PHO

TO: G

HR

V. K

OEN

IGSW

ALD

ARCH

IVE,

RESE

ARCH

INST

ITU

TESE

NCK

ENBE

RG; G

RAPH

IC: N

ATU

RE43

1, 2

99-3

02 (S

EPTE

MBE

R16

, 200

4)

PHO

TOS:

NAT

URE

431,

299

-302

(SEP

TEM

BER

16, 2

004)

GRA

PHIC

: MPI

FO

REV

OLU

TIO

NAR

YAN

THRO

POLO

GY