Evolutionary processes shaping genetic structure in Ethiopia and the Sudans

来自世界各地的个体样本显示出DNA的巨大多样性。然而，导致这种多样性的主要特征却鲜为人知。例如，众所周知，居住在地理位置接近的群体往往与居住在更远的群体具有相似的DNA模式，但什么样的人类学或地形特征最能预测这些相似性？河流是否为促进不同群体之间的相互作用提供了通道，从而导致历史上这些群体之间的DNA交换？自然特征（如山脉）是否为这种互动提供了主要障碍，还是共享语言或宗教不是更重要的障碍？促进遗传多样性的重要特征是否随时间而改变？埃塞俄比亚联邦民主共和国、苏丹共和国和南苏丹共和国表现出极大的文化多样性，例如，有100多种不同的语言和100多个不同的民族生活在其中。人们对这些民族的历史知之甚少，历史记录往往不完整或相互矛盾。最近的研究表明，这些群体的DNA也高度多样化。这种DNA提供了一种解决历史不准确性的有力手段，并确定了上述促进不同群体之间混合的特征，这些特征塑造了该地区数万年来的遗传景观。在这个项目中，我们将开发和应用新的、最先进的统计方法来收集数百个埃塞俄比亚和苏丹人的DNA样本。我们将确定塑造世界上这一独特地区遗传多样性的特征，确定这些地区内不同种族群体交换DNA的历史事件，以及来自国家边界以外来源的DNA贡献。其中一些方法最近被成功地用于探索英国的历史，这是世界上文化和遗传多样性相对较少的一部分（http://www.peopleofthebritishisles.org/）。阐明群体如何在遗传上相互作用的动力学将对理解基因流动在历史上和今天如何在种群中持续存在具有重大意义。了解这一多样化区域的遗传结构也将有助于未来的研究人员设计采样策略，以测试基因组的特定区域是否与常见表型（如身高或疾病状态）相关。东非的这一地区对于研究人类起源也是至关重要的，这里有已知最早的人类化石遗骸，证实了大约20万年前的历史。现代人类最早出现在撒哈拉以南的非洲地区，这一点已经得到了证实。人们认为，埃塞俄比亚和苏丹是撒哈拉以南非洲民族在向世界其他地区殖民时最初迁徙的门户。通过仔细比较该地区人群的DNA与撒哈拉以南非洲以外人群的DNA，我们或许能够推断出这些早期探险家走过的路线，并精确地绘制出迁徙的人类是如何殖民世界的。

Individuals sampled from across the world show great diversity in their DNA. However the primary features that lead to this diversity are poorly understood. For example, it is well-known that groups residing in close geographic proximity often have similar DNA patterns relative to groups residing further away, but what sorts of anthropological or topographical features best predict these similarities? Do rivers provide gateways for promoting interactions among different groups and thus lead to DNA exchange among these groups throughout history? Do natural features such as mountains provide a major barrier to such interactions, or is not sharing a language or religion a more important barrier? Have the important features that promote genetic diversity changed over time? The Federal Democratic Republic of Ethiopian, the Republic of Sudan, and the Republic of South Sudan show great cultural diversity, with for example over 100 different languages spoken and over 100 different ethnic groups living within. The history of many of these peoples are poorly understood, with historical records often incomplete or contradictory. Recent studies have shown that the DNA of these groups are also highly diverse. This DNA provides a powerful means of resolving historical inaccuracies, and identifying the aforementioned features that promote intermixing among the different groups that have shaped the genetic landscape of this region for tens of thousands of years. In this project, we will develop and apply new, state-of-the-art statistical methodology to a novel DNA collection consisting of samples from several hundred Ethiopian and Sudanese individuals. We will identify the features that have shaped the genetic diversity of this unique region of the world, identifying historical events where different ethnic groups within these regions exchanged DNA, as well as DNA contributions from sources outside the countries' borders. Some of this methodology has been successfully used recently to explore the history of the United Kingdom, a part of the world with considerably less cultural and genetic diversity (http://www.peopleofthebritishisles.org/). Elucidating the dynamics of how groups interact genetically will have great implications for understanding how gene flow persists among populations historically and today. Understanding the genetic structure of this diverse region will also help future researchers design sampling strategies for studies testing whether particular regions of the genome are associated with common phenotypes such as height or disease status. This region of east Africa is also vital for studying human origins, housing the earliest known human fossil remains that confirm a history going back approximately 200,000 years. It is well-established that modern humans first arose in sub-Saharan Africa, and it is believed that Ethiopia and the Sudans were the gateway for the initial migrations of peoples out of sub-Saharan Africa when colonizing the rest of the world. By careful comparison of the DNA of the groups from this region with those outside of sub-Saharan Africa, we may be able to infer the routes taken by these early explorers and map out precisely how the world was colonized by migrating humans.