Largest yet survey of human genetic diversity
DNA analyses highlight human differences â?? and similarities.
Scientists have taken an unprecedented look at worldwide genetic diversity to illuminate the history of the world’s populations.
In two papers — one published today in Science1, the other published yesterday in Nature2 — two teams performed the most thorough genetic analysis yet on samples from the Human Genome Diversity Project, which covers more than 50 geographic groups from all over the globe.
The group publishing in Nature looked at 29 different populations; the group publishing in Science examined 51. Both analyzed variations in single letters of DNA, called single nucleotide polymorphisms (SNPs), at hundreds of thousands of sites within the human genome. The group publishing in Nature also examined another source of genetic diversity — so-called 'copy number variants', which involve rearrangements within longer stretches of DNA.
Their analyses provide more evidence to support existing ideas, including the concepts that populations lost genetic variation as they migrated farther from Africa (see On the origin of deleterious mutations), and that it's possible to trace an individual's geographic heritage through their DNA. They also turned up some new findings: the team reporting in Nature found for the first time that copy number variants differ between human populations similarly to SNPs.
“It’s like looking back at the earth with a telescope a thousand times more powerful than what you had before,” says Richard Myers of the Stanford University school of Medicine, part of the team publishing in Science. “You confirm what you already knew from the big picture, but you also start to see islands and rivers and houses where before you just knew there were land masses.”
Both teams’ analyses confirm the genetic similarities that tie together the human family: the world’s groups are far more similar to each other than different, for example, and most people have genetic ancestry tracing back to more than one continent. “A huge amount of our genomes are the same across the world, and that helps to argue against racism in my view,” Myers says (see So similar, yet so different).
Previous studies had either looked at fewer 'markers' — sites of genetic variation — or fewer population groups. For instance, studies of diversity in the HapMap project only include samples from four groups — European, African Yoruba, Han Chinese and Japanese.
The newly released studies reveal more local stories. For instance, Myers and his colleagues say their data support the idea that Han Chinese from the north and south are genetically distinct. This confirms oral histories that describe how persecution drove some Han groups south and led to the establishment of separate ethnic minorities, says the University of Michigan’s Jun Li, who is first author on that paper.
The Science paper also finds genetic similarities between Native American groups and Russians and Yakuts of far northeastern Eurasia. This is probably due to the ancient origin of the Native Americans, who are thought to have migrated from Eurasia to North America over a land bridge tens of thousands of years ago. Some previous studies, including one looking at a thousand sites of DNA, did not pick this up. “We have the ability with this higher level of resolution to see ancient relationships that you couldn’t tell with even a thousand markers,” says Marc Feldman of Stanford University, who worked with Myers and Li.
Li says that he and his University of Michigan colleague Noah Rosenberg, one of the authors of the Nature paper, want to take the analysis of the Human Genome Diversity Project samples even further. The pair would like to sequence genes in the samples that are likely to have evolved differently between groups — such as genes involved in fighting local pathogens.
Some large sequencing projects have already begun (see International genome project launched).
- Li, J.Z. et al., Science, 319, 1100-1104 (2008)
- Jakobsson, M. et al. Nature 451, 998-1003 (2008). doi:10.1038/nature06742