Who sits on the low­est branches in our fam­ily tree? This ques­tion has been nag­ging sci­en­tists for decades. Now, a small skull found in Kenya may solve this rid­dle and put a face on hu­man­ity’s old­est rel­a­tive.

Science Illustrated - - CONTENTS -

An­other (very) tiny piece of the puz­zle of hu­man his­tory falls into place

One late af­ter­noon in February 2014, ex­ca­va­tion as­sis­tant John Ekusi walked away from his col­leagues at a dig site in western Kenya. From habit, Ekusi looked around, scan­ning the ground, and he saw an odd ob­ject. A small, yel­low­ish ball was stick­ing out of the brown sand and an­gled peb­bles at the plain. The ex­ca­va­tion had been go­ing on for years, and the team, headed by an­thro­pol­o­gist Isa­iah Nengo from De Anza Col­lege in Cal­i­for­nia, had al­most given up finding more fos­sils. Ekusi there­fore thought that he had found an an­i­mal bone. In any case, the ex­ca­va­tion team de­cided to take a closer look at the bone.

Once the sci­en­tists had brushed away the sand, a small ape skull emerged. The size and shape re­vealed that the ape be­longed to a species that had be­come ex­tinct ages ago. Analy­ses of the sand showed that the ape lived some 13 m years ago. At this im­por­tant time in his­tory, man took his first steps away from the other apes, but so far, re­searchers have only found few fos­sils from this pe­riod. So Ekusi’s lit­tle ball may be a very im­por­tant piece of the puz­zle.


All liv­ing hu­mans and apes de­rive from a com­mon an­ces­tor. Our branch of pri­mates,

the man-apes, came into be­ing some 20 m years ago, and man then branched out from the other man-apes 7 m years ago.

From fos­sils, sci­en­tists know about early hu­mans’ ap­pear­ance and way of life, but they know al­most noth­ing about the time im­me­di­ately be­fore. From the ge­o­log­i­cal age, the mid­dle Miocene epoch, which stretches from 16 to 11.6 m years ago, sci­en­tists have only found one in­tact cra­nium. Other finds have been few and lim­ited to jaws, parts of the face or a part of the frontal bone. The lack of fos­sils is mainly due to the fact that apes of the time lived in the rain­for­est where bones eas­ily per­ish.

The gap in the fam­ily tree is frus­trat­ing to sci­en­tists, as this pe­riod is de­ci­sive for man’s his­tory. At that time, sev­eral new ape species emerged, and also, men and apes also branched away from each other. Many of the new species died out due to cli­mate change, but one of the sur­vivors is the an­ces­tor to all present­day apes and hu­mans.


The newly found skull is very well pre­served, and at first sight, its shape bore sim­i­lar­i­ties to con­tem­po­rary gib­bons. Yet, the team of sci­en­tists could not im­me­di­ately place their find in the fam­ily tree.

“Sev­eral pri­mates – liv­ing and ex­tinct – have skulls sim­i­lar to the gib­bons, with a small head and short snouts,” ex­plains an­thro­pol­o­gist Christo­pher Gil­bert from The City Univer­sity of New York, one of the sci­en­tists, who has helped an­a­lyze the rare find.

The skull did not have any other traits that could re­veal the ape’s place in the fam­ily three. So the sci­en­tists ex­am­ined the in­te­rior of the fos­sil us­ing ad­vanced X-ray equip­ment and 3D tech­nique. The images showed that the ape still had the roots from its first teeth, while the per­ma­nent teeth had not yet erupted, but lay in a straight line in the jaw.

The ap­pear­ance of the teeth showed that the ape lived of mainly fruit and be­longed to a group of species called Nyan­za­p­ithe­cus by re­searchers, but as the mo­lars were sig­nif­i­cantly larger than in the other mem­bers of the group, the in­fant ape has been cat­e­go­rized as a new species. They named it Alesi, which means an­ces­tor in the lo­cal lan­guage.

The mo­lars sug­gest that Alesi is close to hu­mans in the evo­lu­tion. The sci­en­tists came to the same con­clu­sion when ex­am­in­ing the ape’s in­ner ear. Un­like the gib­bon, whose ear canals are large, Alesi’s are small and semi-cir­cu­lar. The canals con­trol bal­ance, and the large canals en­able the gib­bon to swing from tree to tree safely. With its nar­row ear canals, Alesi would prob­a­bly have been mov­ing at a slower pace.

The find also con­firms the pre­vail­ing the­ory that man’s seg­re­ga­tion from the other apes took place in Africa. Ac­cord­ing to the the­ory, our line sep­a­rated from the other apes 7 m years ago, and hu­mans re­mained at the con­ti­nent for 5 m years be­fore spread­ing to the rest of the world. So all liv­ing hu­mans orig­i­nate from Africa.

“The dis­cov­ery of Alesi shows that its lin­eage was close to the ori­gin of mod­ern-day apes and hu­mans,” says head of the ex­ca­va­tion Isa­iah Nengo. “This knowl­edge is im­por­tant, as it al­lows us to re­con­struct the en­vi­ron­ment and cli­mate, and thus ex­plain how and why the apes de­vel­oped at all.”


By com­bin­ing the sen­si­tive X-ray equip­ment and 3D ren­der­ing, sci­en­tists have been able to ex­am­ine minute de­tails of the fos­sil.

The sci­en­tists have, for ex­am­ple, ex­am­ined the enamel rings of the teeth. They show the age of the ape in the same way as growth rings tell the age of a tree. Based on this, the team of sci­en­tists found that Alesi was 481 days old at the time of death – around 16 months. How the in­fant ape died, the sci­en­tists do not know, but as the skull was cov­ered by a layer of vol­canic ash, the sci­en­tists imag­ine that the in­fant ape died dur­ing an erup­tion from a nearby vol­cano.

Based on the size of the skull and the teeth, the sci­en­tists also es­ti­mate that, as an adult, Alesi would have weighed some 11 kg – which is rather more than an adult gib­bon. Alesi’s gen­der, on the other hand, can­not be es­tab­lished, as the ape died be­fore the char­ac­ter­is­tics in the skull, which show the gen­der, were de­vel­oped.

The next step for the sci­en­tists will be to ex­am­ine the inside of the skull, which has im­prints of the in­fant ape’s brain. This will show the de­vel­op­men­tal stage of Alesi’s brain and help place the ape more pre­cisely in the fam­ily tree. The sci­en­tists will also ex­am­ine bones from fin­gers, back and fore­arm, which were found in 2015 close to the place where John Ekusi dis­cov­ered Alesi. The fos­sils are of the same age as Alesi and may be­long to it. Last, but def­i­nitely not least, the team plans to make a 3D model of Alesi, so that we can fi­nally stand face to face with one of our very first an­ces­tors.

ISA­IAH NENGO HEAD OF EX­CA­VA­TION TEAM With this new knowl­edge, we will be able to ex­plain why the apes evolved into hu­mans.

The ex­ca­va­tion team re­moves sand and loose peb­bles us­ing brushes.

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