人類多樣性的非洲之根

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人類並不像人們常說的那樣，起源於非洲某一地區的單一祖先群體。相反，我們的非洲祖先在形態和文化上是多樣化的，分布在整個大陸。

馬克斯·普朗克人類歷史科學研究所：2018年7月11日發表

中文翻譯：GeneGamma

由英國牛津大學博士後埃莉諾·斯凱里博士(Dr. Eleanor Scerri)和馬克斯·普朗克人類歷史科學研究所(Max Planck Institute for the Science of Human History)的研究人員領導的一個科學聯盟，發現分散在非洲各地的人類祖先，在很大程度上，被多種多樣的棲息地和不斷變化的環境分界線所隔離。比如森林和沙漠。幾千年的隔離造就了人類形體上驚人的多樣性，最終混合塑造成我們現如今的人種。

雖然人們普遍認為我們人類起源於非洲，但很少有人關注我們在非洲大陸上是如何進化的。 許多人認為早期人類祖先起源於一個單一的，相對較大的祖先群體，並或多或少隨機地交換了基因和技術，比如石頭工具（stone tools）。本周發表在《生態學與進化趨勢》(Trends In Ecology and Evolution)的一篇論文中，這一觀點受到了挑戰，不僅是對骨骼(人類學)、石頭(考古學)和基因(群體基因組學)方面的，而且是對過去30萬年來非洲氣候和棲息地新的和更詳細的重建。

來自非洲北部和南部的中石器時代工藝品

埃莉諾·斯凱里博士說到：「石頭工具和其它史前人造物（artifacts）—通常被稱為物質文化（material culture）—在空間和時間上都有顯著的聚集分布。」埃莉諾·斯凱里博士是馬克斯·普朗克人類歷史科學研究所和牛津大學的研究員，也是這項研究的主要作者。「雖然整個大陸都在走向更複雜的物質文化，但這種「現代化」（modernization）顯然不是起源於一個地區，也不是在一個時期發生的。」人類的化石也講述了類似的故事。「當我們觀察過去30萬年前人類骨骼的形態時，我們會發現在不同的地方、不同的時期，古代人和現代人的特徵混合在一起」，克里斯·斯特林格（Chris Stringer）教授說道，他是倫敦自然歷史博物館的研究員和這項研究的合著者之一。「與物質文化一樣，我們確實看到了整個大陸趨向現代人類形態，但在不同的時代，不同的地方出現了不同的現代特徵，一些古老的特徵直到最近才出現。」

一致的基因。「我們很難將我們所見到生活在非洲的人類遺傳模式，與在過去1萬年前、同屬一個祖先的人口的非洲人骨骼中，提取出DNA相調和。」馬克·托馬斯（Mark Thomas）教授說道，他是倫敦大學學院的遺傳學家和這項研究的合著者之一。「我們看到的跡象表明，在過去非常深的地方，連通性（connectivity）降低了，一些非常古老的遺傳譜系，以及單一種群難以維持整體多樣性水平。」

頭顱形狀從細長到球狀的進化變化。後者通過小腦的擴張和頂骨的突起在智人譜系進化。左頭顱：(約3萬年前，非洲)，右頭顱:(約9500年前，黎凡特地區)。

一種生態、生物和文化的拼湊物

為了了解人類形態為何如此細分，以及這些劃分是如何隨著時間而變化的，研究人員研究了非洲過去的氣候和環境，這些氣候和環境提供了一幅不斷變化、通常是孤立的宜居地帶的景像。今天非洲許多最不適宜居住的地區，如撒哈拉沙漠（Sahara），曾經是濕潤和植被茂盛的（wet and green），湖泊和河流交織在一起，還有豐富的野生動物。同樣的，今天一些濕潤的熱帶地區，過去卻曾經是乾旱地區。這些變化的環境驅使（drove）動物群落的細分，許多撒哈拉以南的物種在它們的分布上也表現出類似的系統發育模式（phylogenetic patterns）。這些可居住地帶的不斷變化，意味著人類將經歷許多隔離循環，這將導致當地適應和發展為獨特的物質文化和體格形態（biological makeup），接著是基因和文化上的混合。

遍布非洲的各種化石、工藝品和環境表明，我們的體格形態是在一群生活在非洲大陸的，具有相互聯繫的群體之間產生的，他們的連通性隨著時間而改變。

「這些來自不同領域的融合證據，強調了在人類進化模型中考慮人口結構的重要性。」合著者之一，法國圖盧茲CNRS和葡萄牙里斯本古爾本基安研究所的路內斯·奇希博士說到。「這種複雜的人口細分歷史，導致我們對古代人口規模變化的現有模型提出疑問，也許可以將一些舊的瓶頸重新解釋為連通性的變化」他補充道。

「非洲人類的進化是多地區的。我們的祖先是多種族的。並且我們的物質文化發展也是多元的」埃莉諾·斯凱里博士說道。「我們需要觀察非洲的所有地區，來了解人類的進化。」

譯者簡介：東夷苗裔，伽馬3後人

附原文：

PUBLIC RELEASE: 11-JUL-2018

Our fractured African roots

Humans did not stem from a single ancestral population in one region of Africa, as is often claimed

MAX PLANCK INSTITUTE FOR THE SCIENCE OF HUMAN HISTORY

A scientific consortium led by Dr. Eleanor Scerri, British Academy Postdoctoral Fellow at the University of Oxford and researcher at the Max Planck Institute for the Science of Human History, has found that human ancestors were scattered across Africa, and largely kept apart by a combination of diverse habitats and shifting environmental boundaries, such as forests and deserts. Millennia of separation gave rise to a staggering diversity of human forms, whose mixing ultimately shaped our species.

While it is widely accepted that our species originated in Africa, less attention has been paid to how we evolved within the continent. Many had assumed that early human ancestors originated as a single, relatively large ancestral population, and exchanged genes and technologies like stone tools in a more or less random fashion.

In a paper published in Trends in Ecology and Evolution this week, this view is challenged, not only by the usual study of bones (anthropology), stones (archaeology) and genes (population genomics), but also by new and more detailed reconstructions of Africas climates and habitats over the last 300,000 years.

One species, many origins

"Stone tools and other artifacts - usually referred to as material culture - have remarkably clustered distributions in space and through time," said Dr. Eleanor Scerri, researcher at the Max Planck Institute for the Science of Human History and the University of Oxford, and lead author of the study. "While there is a continental-wide trend towards more sophisticated material culture, this modernization clearly doesnt originate in one region or occur at one time period."

Human fossils tell a similar story. "When we look at the morphology of human bones over the last 300,000 years, we see a complex mix of archaic and modern features in different places and at different times," said Prof. Chris Stringer, researcher at the London Natural History Museum and co-author on the study. "As with the material culture, we do see a continental-wide trend towards the modern human form, but different modern features appear in different places at different times, and some archaic features are present until remarkably recently."

The genes concur. "It is difficult to reconcile the genetic patterns we see in living Africans, and in the DNA extracted from the bones of Africans who lived over the last 10,000 years, with there being one ancestral human population," said Prof. Mark Thomas, geneticist at University College London and co-author on the study. "We see indications of reduced connectivity very deep in the past, some very old genetic lineages, and levels of overall diversity that a single population would struggle to maintain."

An ecological, biological and cultural patchwork

To understand why human populations were so subdivided, and how these divisions changed through time, the researchers looked at the past climates and environments of Africa, which give a picture of shifting and often isolated habitable zones. Many of the most inhospitable regions in Africa today, such as the Sahara, were once wet and green, with interwoven networks of lakes and rivers, and abundant wildlife. Similarly, some tropical regions that are humid and green today were once arid. These shifting environments drove subdivisions within animal communities and numerous sub-Saharan species exhibit similar phylogenetic patterns in their distribution.

The shifting nature of these habitable zones means that human populations would have gone through many cycles of isolation - leading to local adaptation and the development of unique material culture and biological makeup - followed by genetic and cultural mixing.

"Convergent evidence from these different fields stresses the importance of considering population structure in our models of human evolution," says co-author Dr. Lounes Chikhi of the CNRS in Toulouse and Instituto Gulbenkian de Ciência in Lisbon."This complex history of population subdivision should thus lead us to question current models of ancient population size changes, and perhaps re-interpret some of the old bottlenecks as changes in connectivity," he added.

"The evolution of human populations in Africa was multi-regional. Our ancestry was multi-ethnic. And the evolution of our material culture was, well, multi-cultural," said Dr Scerri. "We need to look at all regions of Africa to understand human evolution."