Homo Naledi New Species in Human Lineage Is Found in South African Cave
By JOHN NOBLE WILFORD

Acting on a tip from spelunkers two years ago, scientists in South Africa discovered what the cavers had only dimly glimpsed through a crack in a limestone wall deep in the Rising Star Cave: lots and lots of old bones.

The remains covered the earthen floor beyond the narrow opening. This was, the scientists concluded, a large, dark chamber for the dead of a previously unidentified species of the early human lineage — Homo naledi.

The new hominin species was announced on Thursday by an international team of more than 60 scientists led by Lee R. Berger, an American paleoanthropologist who is a professor of human evolution studies at the University of the Witwatersrand in Johannesburg. The species name, H. naledi, refers to the cave where the bones lay undisturbed for so long; “naledi” means “star” in the local Sesotho language.

In two papers published this week in the open-access journal eLife, the researchers said that the more than 1,550 fossil elements documenting the discovery constituted the largest sample for any hominin species in a single African site, and one of the largest anywhere in the world. Further, the scientists said, that sample is probably a small fraction of the fossils yet to be recovered from the chamber. So far the team has recovered parts of at least 15 individuals.

“With almost every bone in the body represented multiple times, Homo naledi is already practically the best-known fossil member of our lineage,” Dr. Berger said.

The finding, like so many others in science, was the result of pure luck followed by considerable effort.

Two local cavers, Rick Hunter and Steven Tucker, found the narrow entrance to the chamber, measuring no more than seven and a half inches wide. They were skinny enough to squeeze through, and in the light of their headlamps they saw the bones all around them. When they showed the fossil pictures to Pedro Boshoff, a caver who is also a geologist, he alerted Dr. Berger, who organized an investigation.

Just getting into the chamber and bringing out samples proved to be a huge challenge. The narrow opening was the only way in.

Paul Dirks, a geologist at James Cook University in Australia, who was lead author of the journal paper describing the chamber, said the investigators first had a steep climb up a stone block called the Dragon’s Back and then a drop down to the entrance passage — all of this in the total absence of natural light.

For the two extended investigations of the chamber in 2013 and 2014, Dr. Berger rounded up the international team of scientists and then recruited six excavating scientists through notices on social media. One special requirement: They had to be slender enough to crawl through that crack in the wall.

One of the six, who were all women and were called “underground astronauts,” was Marina Elliott of Simon Fraser University in British Columbia. She said the collection and removal of the fossils involved “some of the most difficult and dangerous conditions ever encountered in the search for human origins.”

Besides introducing a new member of the prehuman family, the discovery suggests that some early hominins intentionally deposited bodies of their dead in a remote and largely inaccessible cave chamber, a behavior previously considered limited to modern humans. Some of the scientists referred to the practice as a ritualized treatment of their dead, but by “ritual” they said they meant a deliberate and repeated practice, not necessarily a kind of religious rite.

“It’s very, very fascinating,” said Ian Tattersall, an authority on human evolution at the American Museum of Natural History in New York, who was not involved in the research.

“No question there’s at least one new species here,” he added, “but there may be debate over the Homo designation, though the species is quite different from anything else we have seen.”

A colleague of Dr. Tattersall’s at the museum, Eric Delson, who is a professor at Lehman College of the City University of New York, was also impressed, saying, “Berger does it again!”

Dr. Delson was referring to Dr. Berger’s previous headline discovery, published in 2010, also involving cave deposits near Johannesburg. He found many fewer fossils that time, but enough to conclude that he was looking at a new species, which he named Australopithecus sediba. Geologists said the individuals lived 1.78 million to 1.95 million years ago, when australopithecines and early species of Homo were contemporaries.

Researchers analyzing the H. naledi fossils have not yet nailed down their age, which is difficult to measure because of the muddled chamber sediments and the absence of other fauna remains nearby. Some of its primitive anatomy, like a brain no larger than an average orange, Dr. Berger said, indicated that the species evolved near or at the root of the Homo genus, meaning it must be in excess of 2.5 million to 2.8 million years old. Geologists think the cave is no older than three million years.

The field work and two years of analysis for Dr. Berger’s latest discovery were supported by the University of the Witwatersrand, the National Geographic Society and the South African Department of Science and Technology/National Research Foundation. In addition to the journal articles, the findings will be featured in the October issue of National Geographic Magazine and in a two-hour NOVA/National Geographic documentary to air Wednesday on PBS.

Scientists on the discovery team and those not involved in the research noted the mosaic of contrasting anatomical features, including more modern-looking jaws and teeth and feet, that warrant the hominin’s placement as a species in the genus Homo, not Australopithecus, the genus that includes the famous Lucy species that lived 3.2 million years ago. The hands of the newly discovered specimens reminded some scientists of the earliest previously identified specimens of Homo habilis, who were apparently among the first toolmakers.

At a news conference on Wednesday, John Hawks of the University of Wisconsin, Madison, a senior author of the paper describing the new species, said it was “unlike any other species seen before,” noting that a small skull with a brain one-third the size of modern human braincases was perched atop a very slender body. An average H. naledi was about five feet tall and weighed almost 100 pounds, he said.

南非發現新人種化石 古猿、現代人的混合體

下身像人直立行走 疑有處理遺體習俗

南非人類學家10日宣布，他們在約翰尼斯堡西北約50公里的洞穴深處發現大量原始人骨骼化石，可能屬於未知的新人種，這項發現將有助於深入了解人類的起源和進化。

科學家2013到2014年間在該洞穴共發現骨骼化石1550多塊，包括頭骨、顎骨、牙齒和指骨，分別屬於15個幼年、成年及老年個體，南非金山大學的人類學家10日首次展示這批新發現的原始人骨骼化石。

該洞穴在當地的索托語名為「迪納萊蒂」（Dinaledi），意即「上升之星」，南非研究人員於是將這個新人種命名為「納萊迪人」（Homo naledi）。南非金山大學人類學教授柏格說，這是一個「了不起的發現」，可能會改變學界對人類先祖的認知。

初步研究顯示，納萊迪人身高1.5公尺左右，能夠直立行走，生活在距今250萬至280萬年前。研究人員還指出，納萊迪人的手掌、腕關節和腳與現代人相似，但大腦僅相當於一個橙子大小，只有現代人的三分之一，其上半身結構也較為原始，適合從事攀爬動作，體重約45公斤，混合了古代人猿和現代人的特徵。

目前的分類學不知要如何歸類納萊迪人，若能知這些樣本的年齡或許有幫助，但因洞穴地處偏僻，無法藉分析沉澱物或比對附近的動物。

此外，這些遺骸可能是同伴特意將死者屍體藏於洞穴深處。很多學者認為，存放屍體的行為是人類進化到距今較近的某個時期才形成的習俗。柏格團隊的科學家認為，這種作法可能意味遠古人類就有處理遺體的習俗，但未必代表某種宗教習俗，可能只是一種刻意、反覆進行的作法而已。

此次發掘現場位於斯泰克方丹古生物化石區，是世界上埋藏古人類遺跡最豐富的地區之一，這裡發現的人類先祖化石約占全球總數的一半，為探索人類起源提供大量重要依據。

腦袋橘子般大！是不是「人」 撼動考古學

學者：腦小不屬於人 卻有人類墓葬行為

南非洞穴挖出距今280萬年前的新人種「納萊蒂人」，中研院史語所助理研究員王道還表示，這個證據顯示，過去都靠腦容量來判斷是否為「人屬」，也就是「腦袋比較大」的「人」才能表現社會行為，才算是「人」；但這次發現的「納萊蒂人」屬於「小頭」，卻有著墓葬行為，顯示腦袋容量和行為沒有直接關係，提供定義人屬的新證據，為後續研究投下震撼彈。

中研院史語所助理研究員王道還表示，「納萊蒂人」是否為最早的人，還要有更多證據；過去都認為人屬是250萬年後才出現的，更早前則是「南猿屬」，大約生存在距今400到100萬年前，是目前發現最早的人屬，也被稱為人類的祖先。

王道還表示，南猿屬能被稱為人屬，是因為腦容量較大，過去認為腦子比較大的，才能表現出人特有的行為模式；但這次出土的新人種，雖出現類似有意識的行為，但卻是小腦。

但就研究意義來說，王道還表示，「納萊蒂人」推翻了單純以腦容量來定義是否為人屬的定論，提供了新的證據，這是考古學家第一次發現這麼古老的有意識埋葬行為，非常震撼。他也表示，化石非常殘破，要推斷是否為墓葬行為是個問題，「不一定所有學者都認為是墓葬」。

不過，中研院歷史語言研究所特聘研究員臧振華表示，從年代上來看，納萊蒂人幾乎可說是目前發現最早的「人類」，對考古來說，是非常重要且震撼的發現，幾乎改變對過去的認知，必須給予研究者相當肯定。從目前國外學者發現來看，仍需要更多的材料證據來驗證，尚不能輕易有任何結論。

遺體如何搬進深洞 考倒學者

持火把尋路？當時通道較寬？有別的入口？

科學家發現大堆納萊迪人的骸骨化石時，最感困惑的事莫過於這些骸骨是如何通過層層障礙，進到偏僻、遙遠的洞穴深處？

很明顯的是，沒有人曾住在洞穴裡，因為洞裡沒有留下石頭工具或餐食的痕跡，足以為有人居住提供佐證。

如果是食肉動物把淪為獵物的納萊迪人拖進洞穴，骨頭上應該會留下齒痕，但事實上也沒有。最後一種解釋是骸骨可能被流水沖進洞穴，但洞穴裡卻不見被流水連帶沖進來的石頭和卵石。

柏格教授和他的團隊在過濾一個又一個解釋後，最後只好堅持一個不太可能的結論：亦即這些納萊迪人的遺體是被他們族人刻意安置在洞穴裡。

到目前為止，我們只知道人類或是尼安德塔人這種遠古人類，會以類似儀禮對待死者。所以研究人員未堅稱屬人亞科（hominin）的納萊迪人，有本事拖著屍體穿過狹窄的「超人爬行通道」和驚悚的滑坡進到洞穴，因為這樣的說法已到了離譜的程度。

比較可能的解釋是當時的「超人爬行通道」比較寬，可行走通過；也可能他們並未爬進洞穴，只是把屍體從滑坡上丟下，只要時間一久，愈堆愈高的骸骨便會緩緩地自行滾落到相鄰的洞穴。

然而，要刻意將屍體安置在洞穴，納萊迪人仍必須在完全漆黑中找得到路；要做到這點，他們勢必得有火把才辦得到。

但是腦容量有限的納萊迪人有本事完成這麼複雜的行為，似乎是極不可能的事，所以很多研究人員對這樣的解釋根本不加採信。這些人認為，一定還有另一條容易到達的通道。曾參觀過該化石洞穴的學者李基就說：「一定還有另一個入口尚未找到。」

年輕人地穴探險 竟別有洞天

納萊迪人由兩名洞穴探險愛好者無意間發現，其中塔克當時只是不想擋住同伴韓特的路，慢慢移到旁邊，結果進入名為「上升5之星」的洞穴網裂縫，進而獲得重大發現。

他聽說過這個裂縫。雖然曾經下去20多次，卻從未注意到骨骸，也不知道有無其他探查者嘗試下去。他打開頭燈，探照黑暗的裂縫，看不到黑暗的盡頭。他知道，至少有一名探查者曾經往下看，最後認為下去太危險而未再繼續。塔克開始以兩腳在下的姿勢往下降，進入狹窄的垂直裂口。

27歲的塔克解釋他決定冒險一試的原因時說：「發現新事物令人興奮。」塔克身材瘦而結實，正好可以進入裂縫。他繼續下降將近12公尺。

塔克以拱起兩肩、突出兩肘的姿勢下降。他說：「開口寬18公分，尖突的岩塊自每一個方向向你刺來。當我到達底部時，它突然成為一個大型洞室。頂部懸掛令人驚奇的鐘乳石。」

約翰尼斯堡金山大學說，兩人探勘的這片洞穴丘陵草地占地5萬公頃，所發現的人類祖先化石約占全球總數的40%，考古學界稱它「人類的搖籃」。不過塔克進入之前，這個洞室內的化石顯然從未被發現。

在這個如今名為「納萊迪洞室」的空間，塔克的頭燈照亮純白岩層。塔克與韓特發現新的洞穴地形，接著看到散落在洞室地面的化石。

塔克說：「你可以看到幾塊頭骨化石突出地面。當然，我們當時根本不知道我們已經發現什麼……最早使我們感到有興趣的是，這些頭骨化石相當大。當初沒有燈光與防護裝備的東西究竟如何來到這裡？」

一塊近乎完整的下顎骨化石使他們知道，他們已經發現幾乎屬於人類的化石。

兩人的攝影機電池已經沒電。一周後，他們再度穿越這個洞穴，拍下他們的最新發現。

他們把這些照片交給地質學家波修夫，後者再通知古生物學家柏格。塔克與韓特直到看到柏格如獲至寶的興奮神情時，才知道他們的發現意義重大。

塔克與其他探查者志願尋找將近兩年；為了將骨骸帶出，柏格徵求具有科學背景、洞穴經驗、身材瘦小的人幫忙，最後選出六名女性，柏格說，他們是「地下太空人」。

原文參照：
http://www.nytimes.com/2015/09/11/science/south-africa-fossils-new-species-human-ancestor-homo-naledi.html

紐約時報中文版翻譯：
http://cn.nytimes.com/science/20150911/c11fossils/zh-hant/

Video：Lee R. Berger, a professor of human evolution studies at the University of the Witwatersrand in Johannesburg, unveiled a previously unidentified species of the early human lineage — Homo naledi.
http://www.nytimes.com/video/science/100000003901516/researchers-reveal-new-human-species.html

2015-09-11．聯合晚報．A1/A4．要聞/焦點 國際新聞組/編譯陳澄和/陳世欽