journal Science<\/a>.<\/p>\nThe scientists\u2019 method reconstructs genealogies, or maps showing where different pieces of DNA came from and how they were passed down, revealing branches of our evolutionary past.<\/p>\n
\u201cThe most fundamental question that most of us have is, \u2018Why are we here? Where do we come from?\u2019 And these genealogies really allow us to look into the past in a way that we have not been able to do before,\u201d said Priya Moorjani, study coauthor and an associate professor in the department of molecular and cell biology at the University of California, Berkeley.<\/p>\n
Moorjani added that the discovery allows for further investigation into why some hominin groups survived while others disappeared. Understanding the genetic contributions of our various ancestors can help answer that question while also revealing how humans adapted to their environments and why certain diseases affect us today, she said.<\/p>\n
Hunting for ghost lineages<\/p>\n
Modern humans first moved out of Africa around 50,000 years ago. This migration of Homo sapiens is what led to interbreeding with the Neanderthals and Denisovans in Eurasia. However, the newly detected lineages add more to the story.<\/p>\n
One of the unknown ghost ancestors described in the new study likely interbred with humans in Africa before the migration event. The researchers estimate that DNA inherited from this lineage makes up about 0.5% to 1% of the genomes of people living today \u2014 almost the same percentage as Neanderthal DNA currently found in many modern humans.<\/p>\n
The second lineage is much older. The researchers refer to it as a \u201csuper-archaic\u201d ancestor because it traces back to a branch of the human family tree that split roughly 1.8 million years ago. This hominin appears to have interbred with Denisovans in Eurasia more than 200,000 years ago, with some of its DNA eventually reaching modern humans through our interbreeding with Denisovans.<\/p>\n
To uncover these ghost ancestors, researchers developed a new computer-based method, called TRACE, that can search contemporary human genomes for clues left by long-lost populations.<\/p>\n
\u201cOur genomes are mosaics of little bits of DNA from all our ancestors, and so in different parts of our genome we have a different family tree,\u201d Moorjani explained. Some branches of those family trees are relatively recent, while others extend much further into the past. DNA inherited from ancient relatives such as Neanderthals, for example, sits on these deeper branches. TRACE searches across the genome for far back lineages that could point to ancestry from previously unknown populations.<\/p>\n
The researchers tested TRACE on more than 500 modern human genomes from current populations across Africa, Europe and Asia. They found traces of the more recent ghost ancestry in every population they studied, pointing to a lineage that must have contributed DNA to the ancestors of modern humans before our species\u2019 major migration out of Africa.<\/p>\n
\u201cIf you think about going even beyond humans, gene flow and mixing across groups is pretty pervasive across all populations, and so it\u2019s not very surprising that we harbour DNA from different hominin groups,\u201d Moorjani said. \u201cIt\u2019s just that until recently, it\u2019s not been feasible to extract this DNA from people who lived in the past.\u201d<\/p>\n
Identifying mysterious ancestors<\/p>\n
While the researchers cannot yet say which hominin populations these lineages belonged to, they\u2019ve narrowed down possible candidates based on when the lineages diverged on the hominin family tree. One lineage\u2019s estimated time of divergence is consistent with Middle Pleistocene Homo populations in Africa, suggesting it could be Homo heidelbergensis, the researchers wrote in the study.<\/p>\n
Homo heidelbergensis lived from about 700,000 to 200,000 years ago in Africa and Europe. The other much older lineage, the researchers speculate, could be related to Homo erectus from Eurasia. So far, DNA has not been recovered for either hominin group.<\/p>\n
\u201cThe super-archaic finding is particularly exciting because it reveals genetic contributions from a human lineage that lived over a million years ago, despite the absence of any sequenced DNA from that population,\u201d said Arjun Biddanda, a postdoctoral researcher at Johns Hopkins University and a co-first author of the study, in a statement.<\/p>\n
Modern human genomes are largely similar, but vary from individual to individual in small part due to these deep ancestral lineages, which have contributed some rare but noticeable differences to genomes, explained John Hawks, a paleoanthropologist and professor at the University of Wisconsin\u2013Madison. Hawks was not involved with the new study.<\/p>\n
\u201cToday we have a tendency to focus on differences between people that seem large, but are actually superficial \u2014 like skin colour or facial appearance,\u201d Hawks said in an email. \u201cThese differences among living people are actually very tiny compared to the ancestors we all evolved from, and those ancestors found ways to interact and survive with each other. That\u2019s our heritage, and it\u2019s one that matters even more than ever.\u201d<\/p>\n
The discovery of the younger ghost lineage \u201cplaces the time of mixture well before the mixture with Neanderthals, and shows that it affects all populations living today,\u201d Hawks added.<\/p>\n
The researchers said they hope that the TRACE method will uncover more hidden lineages in our species as well as across other animal species. But the researchers agree that the best new evidence will come from DNA extracted directly from ancient fossils.<\/p>\n
For now, however, the clues left in modern DNA are the closest scientists can get to these long-lost ancestors.<\/p>\n
\u201cRandomly, two people from the world might inherit the same piece of DNA from an ancestor who we didn\u2019t have an idea of before, but now we actually know,\u201d said the study\u2019s co-first author Yulin Zhang, a doctoral student of computational biology at UC Berkeley. \u201cFrom this mysterious ancestor, we have something in common from another angle.\u201d<\/p>\n
By Taylor Nicioli, CNN<\/p>\n
Related Stories<\/p>\n","protected":false},"excerpt":{"rendered":"Clues emerging from DNA could unlock the mystery of human ancestors that are missing from the fossil record…\n","protected":false},"author":2,"featured_media":873427,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[712,49,48,66],"class_list":["post-873426","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-apple-news","tag-ca","tag-canada","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/873426","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=873426"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/873426\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/873427"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=873426"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=873426"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=873426"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}