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“Lucy’s Baby”: pre-human fossil dazzles scientists

Sept. 20, 2006
Special to World Science  

Re­search­ers say they’ve unearthed the pos­sib­ly most com­plete known fos­sil of a fore­bear of hu­mans: a ba­by of the same spe­cies as the famed “Lu­cy” fos­sil found in 1974.

Human-like be­low the waist, ape-like above, the tot is a “once-in-a-life­time” find, said Ethi­o­pi­an pa­le­oan­thro­po­lo­gist Ze­re­se­nay Al­em­se­ged, who led the sci­en­tif­ic team cre­d­ited with the dis­cov­er­y.

De­scribed as the skull of an Aus­tra­lo­pi­the­cus afa­ren­sis ba­by, this meas­ures about 12 cm (5 inches) from the bot­tom of the chin to the top of the head ver­ti­cal­ly. (Cour­te­sy Ze­re­se­nay Al­em­seged; © Au­tho­r­i­ty for Re­search and Con­ser­va­tion of Cul­tur­al He­r­i­ta­ges).

The find re­vived me­m­o­ries of “Lu­cy,” be­lieved to be a fe­male in her mid-20s and hailed, when dis­cov­ered, as the most com­p­lete known ske­l­e­ton of a pre-hu­man ho­m­i­nid. A ho­m­i­nid is a spe­cies on the hu­man branch of the ev­o­lu­tion­a­ry tree.

The new spe­ci­men, dubbed “Lu­cy’s ba­by” by some—though it’s ac­tu­al­ly thought to have lived a bit ear­li­er than Lu­cy—is like­wise caus­ing a stir over its splen­did con­di­tion. 

That, sci­en­tists say, makes it a trea­s­ure trove of ad­di­tio­n­al clues to hu­man ori­gins.

Years ago, Lu­cy, in many re­search­ers’ view, over­turned a wide­spread as­sump­tion: that our an­ces­tors evolved in­tel­li­gence first and up­right walk­ing la­ter. She was seen to re­fute that be­cause her bones sug­ges­ted at least some up­right-walk­ing abi­l­i­ty, yet a small, ape-like brain. 

This helped re­vive a no­tion pro­posed by Charles Dar­win: that up­right move­ment spurred brain evo­lu­tion by free­ing hands for tool use. Hence­forth, suc­cess in the bat­tle for sur­vi­val would de­pend on ever-bet­ter tool use, and the brains to en­able it. 

Like Lucy, the new­found child shows the marks of a spe­cies able to walk up­right, re­search­ers said; it also of­fers more clues to the ev­o­lu­tion of that skill, and of the brain and speech. It’s a “mine of in­for­ma­tion about a cru­cial stage in hu­man ev­o­lu­tion­ary his­to­ry,” wrote pa­le­o­bi­o­lo­gist Ber­nard Wood of George Wash­ing­ton Uni­ver­si­ty in Wash­ing­ton, D.C., in a com­men­tary in the Sept. 21 is­sue of the re­search jour­nal Na­ture.

The sci­en­tists cred­ited with the find de­s­c­ribed it in ano­ther pa­per in the same is­sue. They es­ti­mat­ed that the in­fant died at age three, pos­si­bly in a flood that al­so bur­ied it in peb­bles and sand, help­ing pre­serve it.

Artist's conception of a mo­ther and child Aus­tra­lo­pi­the­cus afaren­sis. Ad­ult fe­males of the spe­cies were some 3½ feet tall, judg­ing from the "Lucy" spe­ci­men.

Lu­cy and the ba­by, which date to slight­ly more than three mil­lion years ago, are far from the old­est known mem­bers of the hu­man fam­i­ly. 

That dis­tinc­tion be­longs to the chimp-sized Sa­he­lan­thro­pus tchaden­sis or “Toumai Man,” es­ti­mat­ed as sev­en mil­lion years old and found in Cen­tral Af­ri­ca four years ago.

But Lu­cy and the tot—said to re­p­re­sent a lat­er spe­cies, Aus­tra­lo­pi­the­cus afaren­sis—would be part of a burst of hom­i­nid di­ver­si­ty noted in the fossil re­cord from four to two mil­lion years ago.

This is thought to re­flect some of the rich ev­o­lu­tion­a­ry ex­per­i­men­ta­tion that na­ture tossed up on the way to pro­duc­ing our spe­cies, Ho­mo sapi­ens. Ho­minids of that pe­ri­od are col­lec­tive­ly called Aus­tralo­p­iths. Which line­age led to us is un­known, though.

The new­found bun­dle of bones, found like Lu­cy in the Ethi­o­pi­an de­sert, was also a fe­male, and lived  about 3.3 mil­lion years ago, its disco­verers said. Lu­cy is thought to have lived 3.2 mil­lion years ago.

“The most im­pres­sive dif­fer­ence be­tween them is that this ba­by has a face,” said team lead­er Ze­re­se­nay (E­thi­o­pi­ans’ first names are their for­mal names.) This face gave away the spe­cies, added Ze­re­se­nay, of the Max Planck In­sti­tute for Ev­o­lu­tion­ary An­thro­pol­o­gy in Leip­zig, German­y. 

Al­so un­like Lu­cy—nick­named after a Beat­les song—the ba­by has fin­gers, a foot and a tor­so. Tooth struc­tures clued re­search­ers in to its rough age and its sex, they said, while the se­di­ments that had trapped it re­vealed its time period. 

Aus­tra­lo­piths in East­ern Af­ri­ca fight off hy­e­nas over a chunk of meat in an im­age by ­pa­leo-art­ist Ste­fa­no Ric­ci (Cour­te­sy S. Ric­ci and Ar­ch­ae­o­lo­gi­cal Mu­se­um of Ca­ma­io­re).

The tot helps ex­p­lain how A. a­fa­ren­sis blur­red ape-hu­man boun­d­a­ries, Ze­re­se­nay said: her shoul­der blades re­sem­b­le a young go­ril­la’s, sug­gest­ing she could climb trees, but her thigh bone is an­g­led like hu­mans’, im­p­ly­ing good up­right walk­ing ab­i­l­i­ty.

Mem­bers of the spe­cies seem to have been fo­r­ag­ing, up­right walk­ers, ca­pa­ble of “climb­ing trees when ne­c­es­sar­y, es­pe­cial­ly when they were lit­tle,” he said.

Ze­re­se­nay first led a band of fos­sil hun­t­ers in­to Eth­i­o­pi­a’s Di­ki­ka re­gion in 1999, re­search­ers re­coun­t­ed. Pun­ish­ing heat, flash floods, ma­la­r­i­a, wild beasts and oc­ca­sion­al shoot­outs be­tween ri­val eth­nic groups plague the zone.

On a shade­less De­cem­ber day the next year, the sci­en­tists re­called, they hunt­ed un­der a pound­ing sun for the prize that had elud­ed them—our ape-like fore­bears. Team mem­ber Tilahun Ge­bre­se­lassie then spot­ted the tot’s face, no big­ger than a mon­key’s, peer­ing out from a dusty slope.

Tucked be­neath it in hard sand­stone were more bones, the whole bun­dle of them no big­ger than a can­te­loupe, one fin­ger still curled in a ti­ny grasp, re­search­ers said. Ze­re­se­nay found a rare ex­am­ple of a hy­oid bone, a throat struc­ture lat­er cru­cial to hu­man speech, he said. This of­fers a glimpse of the ev­o­lu­tion of the voice box, which un­der some the­o­ries is in­t­er­wo­ven with that of speech.

Ze­re­se­nay spent the next five years scratch­ing away rock from the skel­e­ton with a den­tist’s drill, ac­cord­ing to mem­bers of his team.

What killed the ba­by is un­clear. But it seems the an­cient Awash Riv­er rap­id­ly bur­ied the body in a flood, the sci­en­tists said, pre­serv­ing rare de­tails such as a full set of both milk teeth and un­e­rupt­ed adult teeth. The brain cast will help reveal “wheth­er our ear­li­est an­ces­tors grew their brains in the uniquely hu­man way,” said a mem­ber of the re­search group, Fred Spoor of Uni­ver­si­ty Col­lege Lon­don.

One of her hu­manlike knees was com­plete with a knee­cap no big­ger than a dried pea, re­search­ers said. But her up­per bod­y, like Lu­cy’s, had many ape­like fea­tures: small brain, nose flat like a chim­p’s, face pro­ject­ing for­ward. Her two com­plete shoul­der blades are the first found from an Aus­tralo­p­ith, Ze­re­se­nay said; an­a­lyz­ing their func­tion “will be among the ex­cit­ing chal­lenges that we will face.”

Researchers say they’ve found the most complete fossil infant of a forebear of humans: a baby of the same species as the famed “Lucy” fossil unearthed in 1974. Human-like below the waist, ape-like above, it’s a “once-in-a-lifetime” find, said Ethiopian paleoanthropologist Zeresenay Alemseged, who led a scientific team credited with the discovery. The announcement Wednesday revived memories of the Lucy fossil, believed to come from a female in her mid-20s and hailed, when found, as the most complete skeleton of a pre-human hominid yet unearthed. A hominid is a species on the human branch of the evolutionary tree. The newfound skeleton, loosely dubbed “Lucy’s baby” by some—though it’s actually thought to have lived a bit earlier than Lucy—it’s causing a similar stir over its splendid condition. That, scientists say, makes it a treasure trove of additional clues to human origins. Lucy persuaded many researchers that a common assumption—that our ancestors evolved intelligence first, then upright walking—was wrong, because her bones betrayed some upright-walking ability, yet a small, apelike brain. This, some argue, backs an idea of Charles Darwin: that upright movement stimulated greater intelligence by freeing up the hands for tool use, which demands brainpower. The baby also shows upright walking ability, and offers further clues to that and the evolution of the brain and language, researchers claimed. It’s a “mine of information about a crucial stage in human evolutionary history,” wrote paleobiologist Bernard Wood of George Washington University in Washington, D.C., in a commentary in the Sept. 21 issue of the research journal Nature. The scientists credited with the find reported the details in a paper in the same issue. They estimated that the infant died at age three, possibly in a flood that also buried it in pebbles and sand, helping fossilize it. Lucy and the baby, which date to slightly more than three million years ago, are far from the oldest known members of the human family. That distinction belongs Sahelanthropus tchadensis or “Toumai man,” a chimp-sized creature estimated to be seven million years old and unearthed in Central Africa four years ago. But Lucy and the tot—said to be representatives of a later species, Australopithecus afarensis—would be part of an explosion of hominid diversity thought to have occurred between four and two million years ago. That diversity is thought to reflect some of the rich evolutionary experimentation that nature threw up on the way to producing our species, Homo sapiens. Hominids of this period are collectively called Australopiths. Which lineage led to us is unknown, though. The newfound bundle of bones, found like Lucy in Ethiopia, is arguably the best fossil of its species ever found, its discoverers said. They estimated it lived 3.3 million years ago, compared to 3.2 million for Lucy, and was also female. “The most impressive difference between them is that this baby has a face,” said Zeresenay, the team leader (Ethiopians’ first names are their formal names.) This face gave away the species as A. afarensis, added Zeresenay, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Also unlike Lucy—whose nickname comes from a Beatles song—the baby has fingers, a foot and a torso. The tot offers new clues to how the creature blurred ape-human boundaries, Zeresenay said. Her shoulder blades resemble a young gorilla’s, suggesting she could climb trees, he argued; but her thigh bone is angled like humans’, implying good upright walking ability. The species seems to have consisted of foraging, upright walkers, capable of “climbing trees when necessary, especially when they were little,” he said. Zeresenay first led a band of fossil hunters into Ethiopia’s Dikika region in 1999, researchers recounted. Punishing heat, flash floods, malaria, wild beasts and occasional shootouts between rival ethnic groups plague the zone. On a shadeless December day the next year, the scientists recalled, they hunted under a pounding sun for the prize that had eluded them—our ape-like forebears. Team member Tilahun Gebreselassie then spotted the tot’s face, no bigger than a monkey’s, peering out from a dusty slope. Tucked beneath it in hard sandstone were more bones, the whole bundle of them no bigger than a canteloupe, one finger was still curled in a tiny grasp. Where her throat had been, Zeresenay found a rare example of a hyoid bone, which later was crucial to human speech, he said. This offered a glimpse of the evolution of the voice box. Zeresenay spent the next five years scratching away rock from the skeleton with a dentist’s drill, members of his team said. What killed the baby is unclear. But it seems the ancient Awash River rapidly buried the body in a flood, according to the scientists, preserving rare details such as a full set of both milk teeth and unerupted adult teeth. The find “will shed on how this species lived and grew,” said Arizona State University’s Bill Kimbel, a coauthor of the Nature paper. “With the entire brain cast we can now examine whether our earliest ancestors grew their brains in the uniquely human way,” added another coauthor, Fred Spoor of University College London. One of her humanlike knees was complete with a kneecap no bigger than a dried pea, researchers said. But her upper body, like Lucy’s, had many apelike features. Her brain was small, her nose flat like a chimp’s, and her face long and projecting. Her finger bones were curved and almost as long as a chimp’s. Her two complete shoulder blades are the first ever found from an australopith individual, Zeresenay said; “analyzing the functional significance of these bones in more detail will be among the exciting challenges that we will face.”