[ti:Modern Genome Data Suggests How Homo Sapiens Developed in Africa] [by:www.51voa.com] [00:00.00]更多听力请访问51VOA.COM [00:01.28]The human species, Homo sapiens, [00:04.56]developed about 300,000 years ago in Africa. [00:10.76]The oldest-known Homo sapien fossils [00:13.88]were discovered at a place in Morocco [00:17.48]called Jebel Irhoud, between Marrakech and the Atlantic coast. [00:24.92]But very few fossils remain from that time. [00:30.40]The fossils that do remain come from areas [00:34.40]very far apart from one another. [00:38.28]Some of them were discovered in Ethiopia, [00:41.76]while others were found in South Africa. [00:46.96]That makes it difficult for scientists to know [00:50.72]how our species developed and spread across the African continent. [00:57.84]But a new study using genome data [01:01.12]from modern-day African populations [01:04.68]may help explain that development and spread. [01:09.12]The study suggests that many ancestral groups [01:14.84]moved across geographic areas and mixed with each other [01:20.08]over hundreds of thousands of years. [01:24.32]It also found that everyone alive today can connect their ancestry [01:30.76]to at least two different populations that were present in Africa [01:36.36]about a million years. [01:39.04]These results differ from an earlier explanation about our species. [01:46.68]That idea suggested Homo sapiens developed in only a single area [01:53.64]or mixed with a related species. [01:58.60]"All humans share relatively recent common ancestry, [02:04.68]but the story in the deeper past is more complicated [02:10.32]than our species evolving in just a single location [02:15.68]or in isolation," said Aaron Ragsdale. [02:21.80]He is a population geneticist [02:24.64]at the University of Wisconsin-Madison. [02:30.24]He was the lead writer of the study, [02:33.72]which appeared recently in the publication Nature. [02:39.36]Because early groups moved and mixed, [02:43.04]isolated groups did not develop. [02:46.16]When groups are isolated, [02:48.88]they are more likely to become genetically different from other groups. [02:55.40]But the movement and mixing across Africa [02:59.36]kept the groups' genetic material similar. [03:04.00]Scientists looked at genome data from 290 modern-day people, [03:09.96]mostly from four populations from different areas in Africa. [03:16.80]The four groups were also genetically diverse. [03:21.96]The scientists could then connect both similarities and differences [03:27.80]among these four groups to genetic connections dating back [03:33.16]hundreds of thousands of years. [03:37.32]The groups included the following: [03:40.28]85 individuals from a West African group [03:45.12]called the Mende from Sierra Leone; [03:49.64]44 individuals from the Nama Khoe-San group from southern Africa; [03:56.52]46 individuals from the Amhara and Oromo groups in Ethiopia; [04:03.68]and 23 individuals from the Gumuz group, also from Ethiopia. [04:11.52]The scientists also included 91 Europeans. [04:17.36]This was to measure the possible effect of [04:21.20]European and Neanderthal ancestry on the genome. [04:27.20]Neanderthals are an extinct human species [04:31.00]and were found mostly in Europe until about 40,000 years ago. [04:38.36]Scientists say they have not yet found ancient DNA [04:43.04]from the few fossils dating to the time around 300,000 years ago. [04:50.80]However, the genome data from modern populations [04:55.36]can help them form a picture of how Homo sapiens developed. [05:01.92]Study co-writer Simon Gravel [05:04.80]is a geneticist at McGill University in Montreal, Canada. [05:11.68]He said, "The relatedness among contemporary humans [05:16.56]contains a lot of information about this chain of events." [05:22.80]I'm Andrew Smith. 更多听力请访问51VOA.COM