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　　Clues to a ‘ghost’ species of ancient human found in saliva

　　唾液中发现远古人类的“幽灵”物种线索

　　In saliva, scientists have found hints that a “ghost” species of archaic humans may have contributed genetic material to ancestors of people living in Sub-Saharan Africa today.

　　在唾液中，科学家们发现了一些迹象，表明古代人类的“幽灵”物种可能向生活在撒哈拉以南非洲的人类祖先提供了遗传物质。

　　The research adds to a growing body of evidence suggesting that sexual rendezvous between different archaic human species may not have been unusual.

　　这项研究目前证据越来越多，研究成果表明不同古代人类物种之间的性约会可能并不罕见。

　　Past studies have concluded that the forebears of modern humans in Asia and Europe interbred with other early hominin species, including Neanderthals and Denisovans. The new research is among more recent genetic analyses indicating that ancient Africans also had trysts with other early hominins.

　　过去的研究已经得出结论，现代人类在亚洲和欧洲的祖先与其他早期的人类物种杂交，包括尼安德特人和丹尼索瓦人。最新的基因分析表明，古代非洲人也曾与其他早期人类进行过幽会。

　　“It seems that interbreeding between different early hominin species is not the exception — it’s the norm,” says Omer Gokcumen, PhD, an assistant professor of biological sciences in the University at Buffalo College of Arts and Sciences.

　　水牛城艺术与科学学院生物科学助理教授Omer Gokcumen博士说:“似乎早期人类不同物种之间的杂交并不是特例，而是一种规则。”

　　“Our research traced the evolution of an important mucin protein called MUC7 that is found in saliva,” he says. “When we looked at the history of the gene that codes for the protein, we see the signature of archaic admixture in modern day Sub-Saharan African populations.”

　　他说:“在研究过程中，我们追踪了在唾液中发现的一种重要粘液蛋白MUC7的进化过程。”“当我们研究编码蛋白质的基因历史时，我们看到了现代撒哈拉以南非洲人的古人类杂交特征。”

　　The research was published on July 21 in the journal Molecular Biology and Evolution. The study was led by Gokcumen and Stefan Ruhl, DDS, PhD, a professor of oral biology in UB’s School of Dental Medicine.

　　这项研究发表在7月21日的《分子生物学与进化》杂志上。这项研究由Gokcumen和药物传递博士Stefan Ruhl牵头，他是UB医学院口腔生物学教授。

　　A tantalising clue in saliva

　　唾液中诱人的线索

　　The scientists came upon their findings while researching the purpose and origins of the MUC7 protein, which helps give spit its slimy consistency and binds to microbes, potentially helping to rid the body of disease-causing bacteria.

　　科学家们在研究MUC7蛋白的目的和起源时获得了新发现，该蛋白可以帮助唾液粘稠，并与微生物结合，潜在地帮助清除体内致病细菌。

　　As part of this investigation, the team examined the MUC7 gene in more than 2,500 modern human genomes. The analysis yielded a surprise: A group of genomes from Sub-Saharan Africa had a version of the gene that was wildly different from versions found in other modern humans.

　　作为这项调查的一部分，研究小组在2500多个现代人类基因组中检测了MUC7基因。这一分析产生了一个惊人的数据：一组来自撒哈拉以南非洲的基因组有一个版本的基因与其他现代人类的版本大相径庭。

　　The Sub-Saharan variant was so distinctive that Neanderthal and Denisovan MUC7 genes matched more closely with those of other modern humans than the Sub-Saharan outlier did.

　　撒哈拉沙漠以南地区的差异非常明显，尼安德特人和丹尼索瓦人的MUC7基因与其他现代人类的基因更接近于撒哈拉以南地区。

　　“Based on our analysis, the most plausible explanation for this extreme variation is archaic introgression — the introduction of genetic material from a ‘ghost’ species of ancient hominins,” Gokcumen says. “This unknown human relative could be a species that has been discovered, such as a subspecies of Homo erectus, or an undiscovered hominin. We call it a ‘ghost’ species because we don’t have the fossils.”

　　Gokcumen说:“根据我们的分析，这种极端变异最合理的解释是古老的基因渗入—从一个‘幽灵’的远古人类物种中引入遗传物质。”这个未知的人类亲戚可能是已经被发现的物种，比如直立人的亚种，或者是未被发现的人类。我们称它为“幽灵”物种，因为我们没有化石。

　　Given the rate that genes mutate during the course of evolution, the team calculated that the ancestors of people who carry the Sub-Saharan MUC7 variant interbred with another ancient human species as recently as 150,000 years ago, after the two species’ evolutionary path diverged from each other some 1.5 to 2 million years ago.

　　鉴于在进化的过程中的基因变异率，考虑到此两种物种的进化轨迹在150万年～200万年就分道扬镳，研究小组计算了其后最近150000年前那位携带撒哈拉以南MUC7基因的人类祖先与另一古老人类物种的杂交。

　　Why MUC7 matters

　　MUC7为何重要

　　The scientists were interested in MUC7 because in a previous study they showed that the protein likely evolved to serve an important purpose in humans.

　　科学家们对MUC7感兴趣，因为在之前的一项研究中，他们发现这种蛋白质可能是成人类进化的一个重要目标。

　　In some people, the gene that codes for MUC7 holds six copies of genetic instructions that direct the body to build parts of the corresponding protein. In other people, the gene harbors only five sets of these instructions (known as tandem repeats).

　　在一些人体内，编码MUC7的基因有六份基因指令，指导身体构造相应蛋白质的部分。在其他人群中，基因只提供了5组指令(称为串联重复)。

　　Prior studies by other researchers found that the five-copy version of the gene protected against asthma, but Gokcumen and Ruhl did not see this association when they ran a more detailed analysis.

　　其他研究人员先前的研究发现，这五种基因可以防止哮喘，但Gokcumen和Ruhl在进行更详细的分析时并没有看到这种关联。

　　The new study did conclude, however, that MUC7 appears to influence the makeup of the oral microbiome, the collection of bacteria within the mouth. The evidence for this came from an analysis of biological samples from 130 people, which found that different versions of the MUC7 gene were strongly associated with different oral microbiome compositions.

　　然而，这项新研究确实得出结论，MUC7似乎影响口腔微生物组的构成，即口腔内的细菌。来自130人的生物样本分析发现，不同版本的MUC7基因与不同的口腔微生物组成分有密切的联系。

　　“From what we know of MUC7, it makes sense that people with different versions of the MUC7 gene could have different oral microbiomes,” Ruhl says. “The MUC7 protein is thought to enhance the ability of saliva to bind to microbes, an important task that may help prevent disease by clearing unwanted bacteria or other pathogens from the mouth.”

　　“根据我们对MUC7的了解，有不同版本的MUC7基因的人有不同的口腔微生物，这是有道理的，” Ruhl说。“MUC7蛋白被认为能提高唾液与微生物的结合能力，这是一项重要的任务，因为它可以通过清除口腔中多余的细菌或其他病原体来预防疾病。”

　　In addition to Ruhl and Gokcumen, the research team included Duo “Erica” Xu, the study’s first author and a UB PhD student in biological sciences; Pavlos Pavlidis, PhD, and Nikolaos Alachiotis, PhD, of the Foundation for Research and Technology — Hellas in Greece; Colin Flanagan, a UB undergraduate who has completed his degree in biological sciences; Ran Blekhman, PhD, of the University of Minnesota; and Michael DeGiorgio, PhD, of Pennsylvania State University.

　　除了Ruhl和Gokcumen，研究小组还有Duo “Erica” Xu，该论文研究的第一作者，乌兰巴托生物科学博士生;研究与技术基金会的Pavlos Pavlidis博士和Nikolaos Alachioti博士，希腊的Hellas;已完成本科生物科学学位的乌兰巴托的Colin Flanagan;明尼苏达大学的Ran Blekhman博士;宾夕法尼亚州立大学的Michael DeGiorgio博士。

　　The research was funded primarily by the University at Buffalo Research Foundation, with additional support from InnovCrete and the National Institute of Dental and Craniofacial Research.

　　这项研究主要由布法罗研究基金会的一所大学提供资金，并得到了创新克里特和美国国家牙科和颅面研究协会的额外支持。