Featured Research

from universities, journals, and other organizations

Interbreeding between modern humans and evolutionary cousins gave healthy immune system boost to human genome, study finds

Date:
August 25, 2011
Source:
Stanford University Medical Center
Summary:
For a few years now, scientists have known that humans and their evolutionary cousins had some casual flings, but now it appears that these liaisons led to a more meaningful relationship. Interbreeding between modern humans and close relatives -- including Neanderthals and the recently discovered Denisovans -- has endowed some human gene pools with beneficial versions of immune system genes, researchers report in a new study.

Laurent Abi-Rached, Paul Norman and Libby Guethlein are co-authors of research on how the genome of geographically-distinct human populations vary in the amount and type of immune-system genes inherited from evolutionary cousins, the Neanderthals and Denisovans. People in Papua New Guinea, for instance, have a particularly high percentage of one type of immune-system gene that is rarely found in people in Africa.
Credit: Norbert von der Groeben

For a few years now, scientists have known that humans and their evolutionary cousins had some casual flings, but now it appears that these liaisons led to a more meaningful relationship.

Sex with Neanderthals and another close relative -- the recently discovered Denisovans -- has endowed some human gene pools with beneficial versions of immune system genes, report researchers at the Stanford University School of Medicine in an article to be published online by the journal Science at the Science Express website on Aug. 25.

Although modern humans, Neanderthals and Denisovans share a common ancestor in Africa, the groups split into separate, distinct populations approximately 400,000 years ago. The Neanderthal lineage migrated northwestward into West Asia and Europe, and the Denisovan lineage moved northeastward into East Asia. The ancestors of modern man stayed in Africa until 65,000 years or so ago, when they expanded into Eurasia and then encountered the other human-like groups. In some cases, the rendezvous were amorous in nature.

Last year, a partial genome sequence of Neanderthals, who died out approximately 30,000 years ago, revealed that these trysts left as much as 4 percent Neanderthal DNA in the genetic blueprint of some present-day humans. Last December, the genome of another human cousin, the extinct Denisovans, made clear that up to 6 percent of some people's genomes are Denisovan in origin.

Now, a team of researchers led by Peter Parham, PhD, professor of structural biology and of microbiology and immunology, has found that these matings had a positive effect on modern human fitness. "The cross breeding wasn't just a random event that happened, it gave something useful to the gene pool of the modern human," said Parham, who is senior author on the study.

The useful gift was the introduction of new variants of immune system genes called the HLA class I genes, which are critical for our body's ability to recognize and destroy pathogens. HLA genes are some of the most variable and adaptable genes in our genome, in part because the rapid evolution of viruses demands flexibility on the part of our immune system.

"The HLA gene system, with its diversity of variants, is like a magnifying glass," said lead author Laurent Abi-Rached, PhD, explaining that it provides a lot more detail about the history of populations than typical gene families. Abi-Rached is a research associate in the Parham lab.

Prior to the sequencing of the Neanderthal and Denisovan genomes, Parham and his group had suspected that at least one HLA variant came from archaic humans. They determined that the variant known as HLA-B*73 is rare in present-day African populations but occurs with significant frequency in West Asian populations. The ethnic distribution of HLA-B*73 and its similarity across populations suggested that it came from a relatively recent co-mingling of modern human and archaic human DNA, which most likely would have happened outside of Africa. Parham's team wanted to discern which archaic humans were the source of the HLA-B*73 gene type. In the last year they have found the answer in the genome sequence of a recently discovered human relative, the Denisovans, whose existence first came to light in 2008 with the discovery of an unfamiliar finger bone and tooth in a cave in Siberia.

By comparing the HLA genes of the archaic humans with modern humans, the researchers were able to show that the HLA-B*73 allele likely came from cross breeding with Denisovans. Little is known about what the Denisovans looked like (the finger bone and the tooth are the only known fossils), but the genome sequence extracted from the finger bone gives insight into where they overlapped with modern humans. Gene flow from the Denisovans into modern humans has left the highest frequency of the HLA-B*73 allele in populations in West Asia, the most likely site for the fortuitous mating to have taken place.

Even in West Asian populations, the HLA-B*73 variant never represents more than 5 percent of all known variants of that gene. However, other human HLA types that arose from ancient matings are found in much greater frequencies. "Certain traits coming from these archaic humans have become the dominant form," said Parham. For example, another HLA gene type, called HLA-A*11, is absent from African populations, but represents up to 64 percent of variants in East Asia and Oceania, with the greatest frequency in people from Papua New Guinea. "The likely interpretation was that these HLA class variants provided an advantage to modern human and so rose to high frequencies," Parham said.

A similar scenario is seen in some HLA gene types found in the Neanderthal genome, which was also sequenced from DNA extracted from ancient bones. These gene variants are common in European and Asian populations but rare in African populations. "We are finding frequencies in Asia and Europe that are far greater than whole genome estimates of archaic DNA in modern human genomes, which is 1 to 6 percent," said Parham. Within one class of HLA gene, the researchers estimate that Europeans owe half of their variants to interbreeding with Neanderthals and Denisovans, Asians owe up to 80 percent and Papua New Guineans, up to 95 percent.

"This is not the pattern seen genome-wide," said Abi-Rached. "The HLA system is unique in its diversity and the strength of natural selection acting on it, but it's possible that other gene systems, particularly the ones under similar pressure for variation, could show a similar pattern."

Other Stanford-affiliated authors include Matthew Jobin, PhD, lecturer in the Department of Anthropology; postdoctoral scholar Subhash Kulkarni, PhD; research assistant Farbod Babrzadeh; visiting scholar Baback Gharizadeh, PhD; and research associates Lisbeth Guethlein, PhD, and Paul Norman, PhD. The Stanford researchers collaborated with colleagues at the Royal Free Hospital, in the United Kingdom; Ankara University, in Turkey; the National Marrow Donor Program, in Minneapolis; the University of Manitoba; the University of Nairobi; the National Cancer Institute; Liverpool University; UCLA; Canadian Blood Services; and UC-Santa Cruz.

The study was funded by National Institutes of Health, the Yerkes Center, the National Science Foundation and the National Cancer Institute.


Story Source:

The above story is based on materials provided by Stanford University Medical Center. The original article was written by Susan L. Young. Note: Materials may be edited for content and length.


Journal Reference:

  1. Laurent Abi-Rached, Matthew J. Jobin, Subhash Kulkarni, Alasdair McWhinnie, Klara Dalva, Loren Gragert, Farbod Babrzadeh, Baback Gharizadeh, Ma Luo, Francis A. Plummer, Joshua Kimani, Mary Carrington, Derek Middleton, Raja Rajalingam, Meral Beksac, Steven G. E. Marsh, Martin Maiers, Lisbeth A. Guethlein, Sofia Tavoularis, Ann‑Margaret Little, Richard E. Green, Paul J. Norman, Peter Parham. The Shaping of Modern Human Immune Systems by Multiregional Admixture with Archaic Humans. Science, 2011; DOI: 10.1126/science.1209202

Cite This Page:

Stanford University Medical Center. "Interbreeding between modern humans and evolutionary cousins gave healthy immune system boost to human genome, study finds." ScienceDaily. ScienceDaily, 25 August 2011. <www.sciencedaily.com/releases/2011/08/110825141635.htm>.
Stanford University Medical Center. (2011, August 25). Interbreeding between modern humans and evolutionary cousins gave healthy immune system boost to human genome, study finds. ScienceDaily. Retrieved October 21, 2014 from www.sciencedaily.com/releases/2011/08/110825141635.htm
Stanford University Medical Center. "Interbreeding between modern humans and evolutionary cousins gave healthy immune system boost to human genome, study finds." ScienceDaily. www.sciencedaily.com/releases/2011/08/110825141635.htm (accessed October 21, 2014).

Share This



More Fossils & Ruins News

Tuesday, October 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Turns Out Jack The Ripper's True Identity Is Still Unknown

Turns Out Jack The Ripper's True Identity Is Still Unknown

Newsy (Oct. 20, 2014) After testing DNA from a shawl found near one of Jack the Ripper's victims, a scientist said he'd identified the killer. New reports refute the claim. Video provided by Newsy
Powered by NewsLook.com
Fish Fossil Shows First-Ever Sex Was Done Side By Side

Fish Fossil Shows First-Ever Sex Was Done Side By Side

Newsy (Oct. 19, 2014) A 380-million-year-old fish may be the first creature to have copulative sex - and it was side by side with arms linked, like square dancers. Video provided by Newsy
Powered by NewsLook.com
As Sweden Hunts For Sub, "Cold War" Comparisons Flourish

As Sweden Hunts For Sub, "Cold War" Comparisons Flourish

Newsy (Oct. 19, 2014) With Sweden on the look-out for a suspected Russian sub, a lot of people are talking about the Cold War, but is it an apt comparison? Video provided by Newsy
Powered by NewsLook.com
So, Kangaroos Didn't Always Hop

So, Kangaroos Didn't Always Hop

Newsy (Oct. 16, 2014) Researchers believe an extinct kangaroo species weighed 500 pounds or more and couldn't hop. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins