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Human nearly extinct 900,000 years ago: study
Our human ancestors almost went extinct about 900,000 years ago due to catastrophic climate changes, a recent study shows.
Modern humans, known as Homo sapiens, emerged in Africa around 300,000 to 200,000 years ago, but genetic research into human evolution is confined largely to the recent 100,000 years. It can't be solved by using ancient DNA, because ancient DNA can't survive long in hot climates.
Hence, a team of researchers from China, Italy and the US developed a novel method called FitCoal (fast infinitesimal time coalescent process) to conduct a census of population on our ancestors.
They analyzed genomic sequences from 3,154 present-day humans and found that our ancestors dwindled to just 1,280 breeding individuals about 930,000 years ago, and the population hovered around for 117,000 years.
"Nearly 98.7 percent of our human ancestors were lost," said Li Haipeng from the Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences (SINH-CAS). "An estimated 65.85% of current genetic diversity may have been lost due to this bottleneck in the Early to Middle Pleistocene era."
The gap in the African fossil records can be explained by this bottleneck in the Early Stone Age as chronological. It coincides with this proposed time period of significant loss of fossil evidence," said Giorgio Manzi at Sapienza University of Rome.
Reasons suggested for this downturn in human ancestral population are mostly climatic. Glaciation events around this time led to changes in temperatures, severe droughts, and loss of other species, potentially used as food sources for ancestral humans.
"The novel finding opens a new field in human evolution because it evokes many questions, such as the places where these individuals lived, how they overcame the catastrophic climate changes, and whether natural selection during the bottleneck has accelerated the evolution of the human brain," said Pan Yi-hsuan from the East China Normal University.
According to Li, it will also shed light on research into human origins, evolution of tumors, brain size change, and even our susceptibility to diabetes.
注释：
Homo: n
表示"n. 人；同性恋者"，means "someone who practices homosexuality; having a sexual attraction to persons of the same sex"，如：Homo is not abnormal. It is just not common. 年的研究,我确信同性恋不是不正常,只是不普遍而已。
sapien: n
表示"智人"，means "of or relating to or characteristic of Homo sapiens"，如：It is thought to have been made by Homo erectus, an ancestor of modern Homo sapiens. 脚印被认为是直立人留下的，直立人是现代智人的祖先
Homo sapiens 表示" 智人(现代人的学名)".
infinitesimal: adj
表示" 极微的；无限小的"，means "infinitely or immeasurably small"，如：The body's annual intake of metallic iron is infinitesimal. 人体对金属铁的年摄入量是微不足道的。
coalescent: adj
表示"同上的"，means "growing together, fusing"，如：Wheat gluten acts as both thickener and coalescent in waterborne interior emulsion coatings. 小麦面筋蛋白在内墙涂料中既起到了成膜剂的作用也起到了增稠剂的作用。
genomic: adj
表示"基因组的；染色体组的"，如：So Collins sketches a three part plan he hopes will guide genomic research. 因此柯林斯拟定了一个由三部分组成的计划，他希望这会指导基因组的研究。
dwindle: v
表示" 减少；缩小"，means " become gradually less or smaller"，如：Those jobs will dwindle in years to come.这些工作以后会逐年减少。
Pleistocene: n
表示" 更新世"，means "from two million to 11 thousand years ago; extensive glaciation of the northern hemisphere; the time of human evolution"，如：The most recent ice age was during the pleistocene. 最近的冰河期是在更新世。
Glaciation
表示" 冰河作用；冻结成冰"，如：These hills were formed by glaciation. 这些山丘是冰川作用形成的。
susceptibility: n
表示" 敏感性；感受性；磁化率"，如：Asthmatics have an increased susceptibility to viral illnesses. 气喘病人对病毒性病变的敏感性增加了。
中文简要说明：
重量级期刊《科学》（Science）刊登一项重塑世人理解远古人类历史进程的研究成果。根据科学家以一种新型模块搭配现代人类DNA数据研究分析估算，93万年前，人类族群98.7%消失，几近灭绝，此后11万7000年期间仅靠1280个具生育能力的个体延续命脉。这项惊人发现也揭开历史长河之中令科学界困扰已久的篇章。
综合英国《每日邮报》、科技新闻网站Interesting Engneering、中国《上海日报》报导，中国科学院上海营养与健康研究所与华东师范大学的团队，利用中国、意大利、美国研究人员开发的创新模块FitCoal（fast infinitesimal time coalescent process），分析3154名现代人类（modern humans）基因定序资料，推估古代人口规模。
分析显示，93万年前，地球进入更新世中期（Middle Pleistocene），气候变迁引发冰河期严寒气候，干旱严重，人类当作食物来源的其他物种灭亡，导致98.7%的人类消失，严苛存亡「瓶颈」持续到81万3000年前。这11万7000年期间，人类仅靠1280个具生育能力的个体延续群体生命，对于现代人类存续构成严重威胁。学界认为尼安德塔人（Neanderthals）、丹尼索瓦人（Denisovans）也活在这个时期，后来均告灭绝。
现代人类（智人）约30万年前至20万年前出现于非洲。当今学界对于人类进化基因研究局限于最近10万年内，由于远古人类的DNA无法在炎热气候下保存，无法透过DNA探究更早的人类。FitCoal新模块问世后，人类群体史研究首度推进到约100万年前。
华东师范大学基因学者潘逸萱说，上述发现为人类进化开启一片新域，也触发许多新的问题，「例如这段期间人类居住何处、如何克服灾难等级的气候变化、这段期间物竞天择是否加速人类大脑进化」。
研究团队强调，人类约81.3万年前开始懂得用火，加上气候条件好转，可能是人类数量回升关键因素。
中国科学院上海营养与健康研究所群体遗传学者李海鹏说，现今的遗传多样性多达65.85%在人类祖先近98.7%消失期间随之丧失。如此遗传瓶颈也带来意外转折，艰苦的求存奋斗过程在人类染色体形成过程发挥作用。研究成果也为人类起源、肿瘤进化、脑容量演变、糖尿病基因敏感程度提供线索。
李海鹏说，这些发现只是开端，未来盼能更完整描绘更新世早期至中期人类演进过程，继续揭开人类先祖与进化之谜。
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