• pub­lished: 04 Mar 2015
• views: 6

Sci­en­tists have un­earthed the jaw­bone of what they claim is one of the very first hu­mans. The 2.8 mil­lion-year-old spec­i­men is 400,000 years older than re­searchers thought that our kind first emerged. The dis­cov­ery in Ethiopia sug­gests cli­mate change spurred the tran­si­tion from tree dweller to up­right walk­er. The head of the re­search team told BBC News that the find gives the first in­sight into "the most im­por­tant tran­si­tions in human evo­lu­tion". Prof Brian Vill­moare of the Uni­ver­si­ty of Neva­da in Las Vegas said the dis­cov­ery makes a clear link be­tween an icon­ic 3.2 mil­lion-year-old ho­minin (hu­man-like pri­mate) dis­cov­ered in the same area in 1974, called "Lucy". Could Lucy's kind - which be­longed to the species Aus­tralo­p­ithe­cus afaren­sis - have evolved into the very first prim­i­tive hu­mans? "That's what we are ar­gu­ing," said Prof Vill­moare. But the fos­sil record be­tween the time pe­ri­od when Lucy and her kin were alive and the emer­gence of Homo erec­tus (with its rel­a­tive­ly large brain and hu­man­like body pro­por­tions) two mil­lion years ago is sparse. The 2.8 mil­lion-year-old lower jaw­bone was found in the Le­di-Ger­aru re­search area, Afar Re­gion­al State, by Ethiopi­an stu­dent Cha­lachew Sey­oum. He told BBC News that he was "stunned" when he saw the fos­sil. "The mo­ment I found it, I re­alised that it was im­por­tant, as this is the time pe­ri­od rep­re­sent­ed by few (human) fos­sils in East­ern Africa." The fos­sil is of the left side of the lower jaw, along with five teeth. The back molar teeth are small­er than those of other ho­minins liv­ing in the area and are one of the fea­tures that dis­tin­guish hu­mans from more prim­i­tive an­ces­tors, ac­cord­ing to Pro­fes­sor William Kim­bel, di­rec­tor of Ari­zona State Uni­ver­si­ty's In­sti­tute of Human Ori­gins. "Pre­vi­ous­ly, the old­est fos­sil at­tribut­ed to the genus Homo was an upper jaw from Hadar, Ethiopia, dated to 2.35m years ago," he told BBC News. "So this new dis­cov­ery push­es the human line back by 400,000 years or so, very close to its like­ly (pre-hu­man) an­ces­tor. Its mix of prim­i­tive and ad­vanced fea­tures makes the Ledi jaw a good tran­si­tion­al form be­tween (Lucy) and later hu­mans." A com­put­er re­con­struc­tion of a skull be­long­ing to the species Homo ha­bilis, which has been pub­lished in Na­ture jour­nal, in­di­cates that it may well have been the evo­lu­tion­ary de­scen­dant of the species an­nounced today. The re­searcher in­volved, Prof Fred Spoor of Uni­ver­si­ty Col­lege Lon­don told BBC News that, taken to­geth­er, the new find­ings had lift­ed a veil on a key pe­ri­od in the evo­lu­tion of our species. "By dis­cov­er­ing a new fos­sil and re-analysing an old one we have truly con­tribut­ed to our knowl­edge of our own evo­lu­tion­ary pe­ri­od, stretch­ing over a mil­lion years that had been shroud­ed in mys­tery," he said. Cli­mate change The dat­ing of the jaw­bone might help an­swer one of the key ques­tions in human evo­lu­tion. What caused some apes to climb down from the trees and make their homes on the ground. A sep­a­rate study in Sci­ence hints that a change in cli­mate might have been a fac­tor. An anal­y­sis of the fos­silised plant and an­i­mal life in the area sug­gests that what had once been lush for­est had be­come dry grass­land. As the trees made way for vast plains, apes found a way of ex­ploit­ing the new en­vi­ron­men­tal niche, de­vel­op­ing big­ger brains and be­com­ing less re­liant on hav­ing big jaws and teeth by using tools. Prof Chris Stringer of the Nat­u­ral His­to­ry Mu­se­um in Lon­don de­scribed the dis­cov­ery as a "big story". He says the new species clear­ly does show the ear­li­est step to­ward human char­ac­ter­is­tics, but sug­gests that half a jaw­bone is not enough to tell just how human it was and does not pro­vide enough ev­i­dence to sug­gest that it was this line that led to us. He notes that the emer­gence of hu­man-like char­ac­ter­is­tics was not unique to Ethiopia. "The hu­man-like fea­tures shown by Aus­tralo­p­ithe­cus sed­i­ba in South Africa at around 1.95 mil­lion years ago are like­ly to have de­vel­oped in­de­pen­dent­ly of the pro­cess­es which pro­duced (hu­mans) in East Africa, show­ing that par­al­lel ori­gins are a dis­tinct pos­si­bil­i­ty," Prof Stringer ex­plained. This would sug­gest sev­er­al dif­fer­ent species of hu­mans co-ex­ist­ing in Africa around two mil­lion years ago with only one of them sur­viv­ing and even­tu­al­ly evolv­ing into our species, Homo sapi­ens. It is as if na­ture was ex­per­i­ment­ing with dif­fer­ent ver­sions of the same evo­lu­tion­ary con­fig­u­ra­tion until one suc­ceed­ed. Prof Stringer added: "These new stud­ies leave us with an even more com­plex pic­ture of early hu­mans than we thought, and they chal­lenge us to con­sid­er the very def­i­ni­tion of what it is to be human. Are we de­fined by our small teeth and jaws, our large brain, our long legs, tool-mak­ing, or some com­bi­na­tion of these traits?"