原文網址：www.sciencedaily.com/releases/2017/06/170607133241.htm

我們族類的第一位：最早的智人化石

科學家在摩洛哥的Jebel Irhoud發現最古老的智人化石

由(德國萊比錫)馬克斯普朗克演化人類學研究所的Jean-Jacques Hublin和(摩洛哥拉巴特)國立考古學與文化遺產研究所的Abdelouahed Ben-Ncer領導的國際研究團隊，在摩洛哥的Jebel Irhoud發現了智人(Homo sapiens)的化石骨骸，以及石器和其他動物的骨骸。這些骸骨的定年結果為30萬年前，代表了我們所屬物種中有確切定年結果的最古老化石證據，此年代比之前最古老的智人化石還早了10萬年。他們的發現刊登於6月8日的期刊《自然》( Nature)，作者分別為Hublin等人和Richter等人，內容揭露出人類複雜的演化史可能曾在整個非洲大陸上演。

現代人的基因數據和化石遺骸皆指向非洲是我們所屬的物種――智人的起源地點。過往有確切定年結果的智人化石中，最老的是出自於衣索比亞的Omo Kibish考古遺址，年代為19.5萬年前。同樣位於衣索比亞的Herto的智人化石年代則為16萬年前。到目前為止，大多科學家相信現存的所有人類，都是20萬年前左右生活在東非的人類族群的後代子孫。古人類學家Jean-Jacques Hublin表示：「過去我們認為在20萬年前的東非有一處人類搖籃，但我們的新數據顯示30萬年前左右整個非洲大陸上都有智人的蹤跡。早在智人離開非洲散布出去之前，他們就已經踏遍非洲內部了。」

早在1960年代，摩洛哥的Jebel Irhoud遺址就因為擁有人類化石和石器時代中期的工藝品而為人所知。然而，Irhoud所屬的人種一直都因為無法確定其地質年代而不甚清楚。從2004年開始的新挖掘計畫成果為在現地找到了新的智人化石，將發現數量從6提升至22。這些發現確立了Jebel Irhoud的重要性，其為石器時代中期最豐富也最古老的人屬出土場址，紀錄了智人的早期發展階段。Jebel Irhoud的化石遺骸包含了顱骨、牙齒和長骨，至少隸屬於5個個體。研究人員利用同一地點沉積物中發現的打火燧石，進行熱螢光定年法(thermoluminescence dating method)來得到這些發現的精確定年數據。從燧石得到的年代大致是30萬年前，因此可以將我們物種的起源年代往前回推10萬年。

Daniel Richter表示；「在非洲，同年代的考古遺址極少擁有良好的定年結果，但我們很幸運地發現Jebel Irhoud的燧石製品中有許多以前曾被加熱過。」他是位於(德國)萊比錫的馬克斯普朗克演化人類學研究所的地質定年專家，現在也任職於Freiberg Instruments GmbH。「這讓我們可以對燧石製品使用熱螢光定年法，而得到跟人類化石以及上方層位一致的定年結果。」此外，團隊也可以重新計算1960年代於Jebel Irhoud發現的三具下顎骨的直接定年結果。這些下顎骨之前利用一種特別的電子自旋共振定年法(electron spin resonance dating method)，得到的年代為16萬年前。運用Jebel Irhoud沉積物新的放射性測量結果，和原理改良後的同一方法，新的化石年代計算結果跟熱螢光定年年代相當一致，比過往認為得早上許多。Richter補充：「我們使用最先進的定年技術並且採用最保守的方法來精確得出Irhoud的年代。」

現代人的頭骨具有數個特徵而可以跟我們的祖先和近親化石區分：包括小巧且纖細的臉部，以及球形的顱骨。Jebel Irhoud的化石具有狀似現代人的臉部和牙齒，但龐大的顱骨看起來卻比較原始。Hublin和他的同事利用最尖端的微米級電腦斷層掃描，以及根據數百項3D測量數據得到的形狀統計分析，顯示出Jebel Irhoud化石的面貌跟今日生活的現代人幾乎是無法區別。然而，相較於十分現代的面目特徵，Jebel Irhoud化石的頭骨卻保有形態古老的長型顱骨。萊比錫馬克斯普朗克演化人類學研究所的古人類學家Philipp Gunz解釋：「顱骨的內部構造反映出大腦形狀。我們的發現指出現代人的面部特徵在我們物種演化史的早期就已經確立出來；大腦的形狀，可能還有大腦的功能，則是在整個智人譜系中逐漸發展而成。」最近從尼安德塔人和丹尼索瓦人取出的古代DNA跟現代人DNA的對比結果，顯示出影響他們大腦和神經系統的基因有所不同。顱骨形狀在演化上的改變過程，可能因此牽涉了一連串基因變化，其同樣影響了腦區的連結、組織和發育，這是智人之所以不同於我們已滅絕的祖先和近親的理由。

Jebel Irhoud的化石型態和年代，也有助於支持從南非Florisbad找到的謎樣部分頭蓋骨化石是早期智人的說法。因此最早期的智人化石可以在非洲大陸各處發現：摩洛哥的Jebel Irhoud(30萬年前)、南非的Florisbad(26萬年前)以及衣索比亞的Omo Kibish(19.5萬年前)。這代表我們物種的演化史相當複雜，整個非洲大陸可能都參與其中。

Abdelouahed Ben-Ncer表示：「在討論關於我們物種起源的種種爭議時，北非長期以來都處於被忽略的地位。在Jebel Irhoud找到的驚人發現顯示出在智人崛起之時，馬格裡布地區(Maghreb，西北非的大部分地區)跟非洲其餘地方有相當緊密的連結。」

在發現人類化石的沉積物中也含有許多動物化石，顯示出人類狩獵的證據，其中最常出現的物種為羚羊。跟化石一起出現的石器屬於石器時代中期。Jebel Irhoud出土的石器顯示當時最常見的打製技巧為勒瓦婁哇(Levallois)的石核製備技術和利器型式。大多數石器是由運送至此的高品質燧石製成。而在較古老遺址中常常發現的手斧則未在Jebel Irhoud發現。從Jebel Irhoud復原的石器時代中期工藝品，類似的組成也可以在非洲各處發現，傳遞出這可能是一種能讓智人散佈至非洲各處的適應行為。

馬克斯普朗克研究所的考古學家Shannon McPherron表示：「Jebel Irhoud出土的石器跟東非和南非差不多年代的沉積物中找到的看起來十分相似。在石器時代中期出現的這場技術革新，可能跟智人的崛起有關。」從Jebel Irhoud得到的新發現釐清了智人的演化過程，也顯示出我們所屬的物種比之前認為得還要早演化出來。在生理構造和行為模式上出現的改變，使得智人在30萬年前得以分佈到非洲各處。

 

The first of our kind: Oldest homo sapiens

Scientists discover the oldest Homo sapiens fossils at Jebel Irhoud, Morocco

An international research team led by Jean-Jacques Hublin of the Max Planck Institute for Evolutionary Anthropology (Leipzig, Germany) and Abdelouahed Ben-Ncer of the National Institute for Archaeology and Heritage (INSAP, Rabat, Morocco) uncovered fossil bones of Homo sapiens along with stone tools and animal bones at Jebel Irhoud, Morocco. The finds are dated to about 300 thousand years ago and represent the oldest securely dated fossil evidence of our own species. This date is 100 thousand years earlier than the previous oldest Homo sapiens fossils. The discoveries reported in two papers in the June 8th issue of the journal Nature by Hublin et al. and by Richter et al. reveal a complex evolutionary history of humankind that likely involved the entire African continent.

Both genetic data of present day humans and fossil remains point to an African origin of our own species, Homo sapiens. Previously, the oldest securely dated Homo sapiens fossils were known from the site of Omo Kibish in Ethiopia, dated to 195 thousand years ago. At Herto, also in Ethiopia, a Homo sapiens fossil is dated to 160 thousand years ago. Until now, most researchers believed that all humans living today descended from a population that lived in East Africa around 200 thousand years ago. "We used to think that there was a cradle of humankind 200 thousand years ago in east Africa, but our new data reveal that Homo sapiens spread across the entire African continent around 300 thousand years ago. Long before the out-of-Africa dispersal of Homo sapiens, there was dispersal within Africa," says palaeoanthropologist Jean-Jacques Hublin.

The Moroccan site of Jebel Irhoud has been well known since the 1960s for its human fossils and for its Middle Stone Age artefacts. However, the interpretation of the Irhoud hominins has long been complicated by persistent uncertainties surrounding their geological age. The new excavation project, which began in 2004, resulted in the discovery of new Homo sapiens fossils in situ, increasing their number from six to 22. These finds confirm the importance of Jebel Irhoud as the oldest and richest African Middle Stone Age hominin site documenting an early stage of our species. The fossil remains from Jebel Irhoud comprise skulls, teeth, and long bones of at least five individuals. To provide a precise chronology for these finds, researchers used the thermoluminescence dating method on heated flints found in the same deposits. These flints yielded an age of approximately 300 thousand years ago and, therefore, push back the origins of our species by one hundred thousand years.

"Well dated sites of this age are exceptionally rare in Africa, but we were fortunate that so many of the Jebel Irhoud flint artefacts had been heated in the past," says geochronology expert Daniel Richter of the Max Planck Institute in Leipzig (Germany), now with Freiberg Instruments GmbH. Richter explains: "This allowed us to apply thermoluminescence dating methods on the flint artefacts and establish a consistent chronology for the new hominin fossils and the layers above them." In addition, the team was able to recalculate a direct age of the Jebel Irhoud 3 mandible found in the 1960s. This mandible had been previously dated to 160 thousand years ago by a special electron spin resonance dating method. Using new measures of the radioactivity of the Jebel Irhoud sediments and as a result of methodological improvements in the method, this fossil's newly calculated age is in agreement with the thermoluminescence ages and much older than previously realised. "We employed state of the art dating methods and adopted the most conservative approaches to accurately determine the age of Irhoud," adds Richter.

The crania of modern humans living today are characterized by a combination of features that distinguish us from our fossil relatives and ancestors: a small and gracile face, and globular braincase. The fossils from Jebel Irhoud display a modern-looking face and teeth, and a large but more archaic-looking braincase. Hublin and his team used state-of-the-art micro computed tomographic scans and statistical shape analysis based on hundreds of 3D measurements to show that the facial shape of the Jebel Irhoud fossils is almost indistinguishable from that of modern humans living today. In contrast to their modern facial morphology, however, the Jebel Irhoud crania retain a rather elongated archaic shape of the braincase. "The inner shape of the braincase reflects the shape of the brain," explains palaeoanthropologist Philipp Gunz from the Max Planck Institute for Evolutionary Anthropology in Leipzig. "Our findings suggest that modern human facial morphology was established early on in the history of our species, and that brain shape, and possibly brain function, evolved within the Homo sapiens lineage," says Philipp Gunz. Recently, comparisons of ancient DNA extracted from Neanderthals and Denisovans to the DNA of present day humans revealed differences in genes affecting the brain and nervous system. Evolutionary shape changes of the braincase are therefore likely related to a series of genetic changes affecting brain connectivity, organization and development that distinguish Homo sapiens from our extinct ancestors and relatives.

The morphology and age of the fossils from Jebel Irhoud also corroborate the interpretation of an enigmatic partial cranium from Florisbad, South Africa, as an early representative of Homo sapiens. The earliest Homo sapiens fossils are found across the entire African continent: Jebel Irhoud, Morocco (300 thousand years), Florisbad, South Africa (260 thousand years), and Omo Kibish, Ethiopia (195 thousand years). This indicates a complex evolutionary history of our species, possibly involving the whole African continent.

"North Africa has long been neglected in the debates surrounding the origin of our species. The spectacular discoveries from Jebel Irhoud demonstrate the tight connections of the Maghreb with the rest of the African continent at the time of Homo sapiens' emergence," says Abdelouahed Ben-Ncer.

The fossils were found in deposits containing animal bones showing evidence of having been hunted, with the most frequent species being gazelle. The stone tools associated with these fossils belong to the Middle Stone Age. The Jebel Irhoud artefacts show the use of Levallois prepared core techniques and pointed forms are the most common. Most stone tools were made from high quality flint imported into the site. Handaxes, a tool commonly found in older sites, are not present at Jebel Irhoud. Middle Stone Age artefact assemblages such as the one recovered from Jebel Irhoud are found across Africa at this time and likely speak to an adaptation that allowed Homo sapiens to disperse across the continent.

"The stone artefacts from Jebel Irhoud look very similar to ones from deposits of similar age in east Africa and in southern Africa" says Max Planck Institute archaeologist Shannon McPherron. "It is likely that the technological innovations of the Middle Stone Age in Africa are linked to the emergence of Homo sapiens." The new findings from Jebel Irhoud elucidate the evolution of Homo sapiens, and show that our species evolved much earlier than previously thought. The dispersal of Homo sapiens across all of Africa around 300 thousand years is the result of changes in both biology and behaviour.

原始論文：Jean-Jacques Hublin, Abdelouahed Ben-Ncer, Shara E. Bailey, Sarah E. Freidline, Simon Neubauer, Matthew M. Skinner, Inga Bergmann, Adeline Le Cabec, Stefano Benazzi, Katerina Harvati, Philipp Gunz. New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens. Nature, 2017; 546 (7657): 289 DOI: 10.1038/nature22336

引用自：Max-Planck-Gesellschaft. "The first of our kind: Oldest homo sapiens: Scientists discover the oldest Homo sapiens fossils at Jebel Irhoud, Morocco." ScienceDaily. ScienceDaily, 7 June 2017.