在衣索比亞南部進行的跨領域研究破解了東非氣候的脈動，並顯示出氣候變遷的關鍵時期如何影響人類的演化、擴散以及革新。這項結果發表在《自然—地球科學》(Nature
Geoscience)。
位在Chew Bahir的鑽井場址，從280公尺長的岩芯中抽出來的襯管會裝滿取上來的沉積物。圖中的日班工人正齊心協力試圖把襯管拔出來。圖片來源：Frank Schaebitz
研究人員分析湖泊沉積物紀錄中的環境代用指標之後，揭露了東非在過去620,000年以來，依據氣候的變化特性可以分為三個時期，而且也符合人族演化以及擴散過程中轉變的時間。此計畫在東非重要的古人類學場址附近，利用科學深層鑽探取出湖相沉積物並加以分析，藉此探討人類演化史上最晚近的篇章。這項浩大的研究包括了來自6個國家、19個研究單位中的22名研究人員，主持人為科隆大學地理教育研究所的Verena
Foerster博士。文章最近發表在《自然—地球科學》，標題為「東非更新世的氣候變化對人族演化的影響」(Pleistocene climate variability in
eastern Africa influenced hominin evolution)。
儘管在半個多世紀之前就在東非發現了人族化石，現代人與其祖先演化與擴散的過程中，當地環境的變化脈絡卻還是不夠確定。尤其是2,580,000至11,700年前的更新世(或稱冰河期)期間，還沒有高解析度的連續古環境紀錄來瞭解非洲大陸的狀況。
更新世的衣索比亞南部是早期人類生活以及發展的地區，研究團隊從此處的Chew
Bahir盆地中，取出了兩根280公尺長的沉積物連續岩芯。人煙罕至的Chew
Bahir在地質構造上是一個深陷的基盤，相當靠近兩個重要的古人類學與考古學場址：圖爾卡納地區及奧莫基比許。從該地得到如此長時間的紀錄中，這兩根岩芯是迄今最為完整的。它們揭露了不同的氣候如何影響居住在此的人類，使其出現生物以及文化上的轉變。
包含了地球科學、沉積學、微體古生物學、地質學、地理學、地球化學、考古學、年代學以及氣候模擬的跨領域研究團隊齊心協力取出了這兩根沉積物連續岩芯，透過其中的代用指標(像是微體化石或是元素含量的變化)，他們蒐集到的數據可以用來重建此區的氣候歷史。接著考古學家、演化生物學家與演化人類學家再判斷哪些時期的氣候會對人類造成壓力或是形成有利的情況，進而詮釋這些因素如何改變人類的棲地，又會如何影響人類在生物與文化上的演變，以及他們的擴散過程。
詳細來說，科學家發現大約在距今620,000至275,000年前，氣候相對穩定且長期濕潤的時期當中，此區居住著許多種從解剖構造上來說相異的人類族群。然而這段大致穩定且濕潤的漫長時期當中，卻穿插著一系列短暫且劇烈的乾旱事件。它們很有可能讓棲地變得零碎、族群動態出現變化，甚至造成某些局部地域族群滅亡。結果是變得較小、生殖與文化上出現區隔的族群後續得適應劇烈轉變的當地環境，這可能刺激了許多地理分布不同且解剖構造相異的人族族群出現，並且讓我們這些現代人的祖先跟早期的類群分家。
距今大約275,000到60,000年前氣候有著明顯的來回震盪，造成此區域的棲地出現規律的變化，環境屢次從擁有茂盛的植被以及深深的淡水湖變成非常乾燥的地景，廣大的湖泊也縮減成小小的鹹水坑。在此階段，族群組成逐漸從阿舍利工藝(由石頭製成的淚滴型手斧，主要由匠人與直立人製作)轉變成更加複雜的中石器時代科技。這個重要的階段還包括了智人在東非崛起，同時人類在社會、科技與文化上也做出了重大革新，或許能減緩早期智人因為劇烈的環境變遷而受到的衝擊。「更加多樣化的工具以及長途運輸等革新，可能使現代人對於屢次擴大縮小的棲地具備前人所沒有的適應能力，」論文主要作者Foerster博士表示。
距今大約60,000到10,000年前可以看到最為劇烈的環境波動，同時也是整段紀錄中最為乾燥的時期，這或許促成了原住民文化持續地演變下去。科學家相信東非短暫出現的濕潤時期，偶爾會和非洲東北與地中海的多雨時期重疊，因而開通一條主幹大致為南北向、利於人類遷徙的道路。這讓他們可以沿著東非大裂谷系統(EARS)離開非洲而進入黎凡特，促使智人擴散到全球各地。
「有鑑於目前氣候變遷對人類棲地造成的威脅，以及人類活動過度利用了許多自然資源，了解氣候與人類演化之間的關係變得比以往都還要迫切，」Foerster總結。
此研究是「人族考古場址與古湖泊鑽探計畫」(Hominin Sites and Paleolakes
Drilling Project)的一部份。為了衡量不同時間尺度與規模的氣候變遷對早期人類的生活條件所造成的衝擊，該計畫從五座湖泊當中鑽出過去350萬年以來的氣候變遷記錄。這五個位在肯亞和衣索比亞的鑽探地點皆相當靠近重要的古人類學場址，其涵蓋了人類演化過程中的不同階段，而位在伊索比亞南部的場址則探討了人類演化最晚近的篇章。
Key phases of human evolution coincide
with flickers in eastern Africa’s climate
Interdisciplinary research in southern
Ethiopia enabled the deciphering of eastern Africa’s climatic heartbeat and
shows how key phases of climate change influenced human evolution, dispersal
and innovation / publication in ‘Nature
Geoscience’
Three distinct phases of climate variability in
eastern Africa coincided with shifts in hominin evolution and dispersal over
the last 620,000 years, an analysis of environmental proxies from a lake
sediment record has revealed. The project explores the youngest chapter in
human evolution by analysing lacustrine sediments in close vicinity to
paleo-anthropological key sites in eastern Africa using scientific deep
drilling. The research endeavour included more than 22 researchers from 19
institutions in 6 countries, and was led by Dr Verena Foerster at the
University of Cologne’s Institute of Geography Education. The article
‘Pleistocene climate variability in eastern Africa influenced hominin
evolution’ has now appeared in Nature
Geoscience.
Despite more than half a century of hominin fossil
discoveries in eastern Africa, the regional environmental context of the
evolution and dispersal of modern humans and their ancestors is not well
established. Particularly for the Pleistocene (or Ice Age) between 2,580,000 to
11,700 years ago, there are no continuous high-resolution paleo-environmental
records available for the African continent.
The research team extracted two continuous 280-metre
sediment cores from the Chew Bahir Basin in southern Ethiopia, an area where
early humans lived and developed during the Pleistocene. Chew Bahir is very
remotely situated in a deep tectonic basement in close vicinity to the Turkana
area and the Omo-Kibish, key paleo-anthropological and archaeological sites.
The cores yielded the most complete record for such a long period ever
extracted in the area, revealing how different climates influenced the biological
and cultural transformation of humans inhabiting the region.
An interdisciplinary team including geoscientists,
sedimentologists, micro-paleontologists, geologists, geographers, geochemists,
archaeologists, chronologists, and climate modellers worked towards recovering
the two continuous sediment cores, from which so-called proxies (like
microfossils or elemental variations) were used to glean data to reconstruct
the region’s climate history. Archaeologists, evolutionary biologists, and
evolutionary anthropologists then identified phases of climatic stress as well
as more favourable conditions and interpreted how these factors changed human
habitats, influencing human biological and cultural evolution as well as their
dispersal.
Specifically, the scientists found that various
anatomically diverse hominin groups inhabited the area during a phase of long-lasting
and relatively stable humid conditions from approximately 620,000 to 275,000
years BP (Before Present). However, a series of shorter abrupt and extreme arid
pulses interrupted this long generally stable and wet phase. Most likely, this
resulted in a fragmentation of habitats, shifts in population dynamics and even
the extinctions of local populations. As a result, small, reproductively and
culturally isolated populations then had to adapt to dramatically transformed
local environments, likely stimulating the appearance of the many
geographically and anatomically distinct hominin groups and the separation of
our modern human ancestors from archaic groups.
A phase with significant climate swings resulting in
regularly transformed habitats in the area from approximately 275,000 to 60,000
years BP repeatedly resulted in environmental shifts from lush vegetation with
deep fresh water lakes to highly arid landscapes with the extensive lakes
reduced to small saline puddles. In this phase, the population groups gradually
transitioned from Acheulean technologies (oval hand axes made of stone and
primarily associated with Homo ergaster/erectus) to more sophisticated Middle
Stone Age technologies. This crucial phase also encompasses the emergence of
Homo sapiens in eastern Africa as well as key human social, technological, and
cultural innovations that could have buffered early Homo sapiens from the
impacts of severe environmental changes. ‘These innovations, such as more
varied toolkits and long-distance transport, would have equipped modern humans
with an unprecedented adaptability to the repeated expansions and contractions
of habitats,’ said Dr Foerster, the paper’s lead author.
The phase from approximately 60,000 to 10,000 years
BP saw the most extreme environmental fluctuations, but also the most arid
phase of the entire record, which could have acted as a motor for continuous
indigenous cultural change. The scientists believe that the brief alignment of
humid pulses in eastern Africa with wet phases in north-eastern Africa and the
Mediterranean was key to opening favourable migration routes out of Africa on a
roughly north-south axis along the East African Rift System (EARS) and into the
Levant, facilitating the global dispersal of Homo sapiens.
‘In view of current threats to the human habitat from
climate change and the overuse of natural resources through human activity,
understanding how the relationship between climate and human evolution has
become more relevant than ever,’ Foerster concluded.
This research is part of the Hominin Sites and
Paleolakes Drilling Project (HSPDP). In order to evaluate the impact that
different timescales and magnitudes of climatic shifts have had on the living
conditions of early humans, the project has cored five lake archives of climate
change during the last 3.5 million years. All five sites in Kenya and Ethiopia
are located in close vicinity to paleoanthropological key sites covering
various steps in human evolution, with the site in southern Ethiopia exploring
the youngest chapter.
原始論文：Verena Foerster, Asfawossen Asrat, Christopher Bronk Ramsey,
Erik T. Brown, Melissa S. Chapot, Alan Deino, Walter Duesing, Matthew Grove,
Annette Hahn, Annett Junginger, Stefanie Kaboth-Bahr, Christine S. Lane,
Stephan Opitz, Anders Noren, Helen M. Roberts, Mona Stockhecke, Ralph
Tiedemann, Céline M. Vidal, Ralf Vogelsang, Andrew S. Cohen, Henry F. Lamb,
Frank Schaebitz & Martin H. Trauth. Pleistocene climate variability in eastern Africa
influenced hominin evolution. Nature Geoscience, 2022 DOI: 10.1038/s41561-022-01032-y
引用自：University of Cologne. "Key phases of
human evolution coincide with flickers in eastern Africa's climate."
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