Featured Research

from universities, journals, and other organizations

Humans and chimps share genetic strategy in battle against pathogens

Date:
February 14, 2013
Source:
University of Chicago Medical Center
Summary:
A search for long-lived balancing selection has found at least six regions of the genome where humans and chimpanzees share a combination of genetic variants. These human genetic variation dates back to a common ancestor with chimpanzees millions of years ago, before the species split.

A genome-wide analysis searching for evidence of long-lived balancing selection -- where the evolutionary process acts not to select the single best adaptation but to maintain genetic variation in a population -- has uncovered at least six regions of the genome where humans and chimpanzees share the same combination of genetic variants.
Credit: anekoho / Fotolia

A genome-wide analysis searching for evidence of long-lived balancing selection -- where the evolutionary process acts not to select the single best adaptation but to maintain genetic variation in a population -- has uncovered at least six regions of the genome where humans and chimpanzees share the same combination of genetic variants.

The finding, to be published Feb. 14 in the journal Science, suggests that in these regions, human genetic variation dates back to a common ancestor with chimpanzees millions of years ago, before the species split. It also highlights the importance of the dynamic co-evolution of human hosts and their pathogens in maintaining genetic variation.

Balancing selection allows evolution to keep all hereditary options open. The classic human example is the persistence of two versions of the hemoglobin gene: a normal version and hemoglobin S., a mutation that distorts the shape and function of red blood cells. Those who inherit two normal hemoglobin genes are at high risk for malaria, a parasitic disease that infects more than 200 million people each year. Those who inherit one normal gene and one hemoglobin S. gene are partially protected from malaria -- a potentially life-saving benefit. Those with two copies of the gene suffer from sickle-cell anemia, a serious and lifelong circulatory disease.

"When we looked for genetic clues pointing to other, more ancient, examples of balancing selection, we found strong evidence for at least six such regions and weaker evidence for another 119 -- many more than we expected," said study author Molly Przeworski, PhD, professor of human genetics and of ecology and evolution at the University of Chicago.

"We don't yet know what their functions are," she said. None of the six regions codes for a protein. There are clues that they are involved in host-pathogen interactions, "but which pathogens, what immune processes," she said, "we don't know."

The researchers used genetic data from 10 chimpanzees from Western Africa and 59 humans from sub-Saharan Africa who were part of the 1,000 Genomes Project.

The scientists looked for cases in which genetic variations that arose in the ancestor of humans and chimpanzees have been maintained through both lines. The fact that variation in these regions of the genome has persisted for so long argues that they "must have been functionally important over evolutionary time," said Ellen Leffler, a graduate student in Przeworski's laboratory and first author of the study.

The researchers, from the University of Chicago and Oxford University, designed the study to be very conservative. "We wanted to find the cases we believed the most, rather than the most cases," Przeworski said.

Computers sorted snippets of the genetic data from humans and chimps into clusters depending on how similar the subjects were to each other. For almost every snippet, they found a cluster of humans and a separate cluster of chimpanzees, as expected. But there were a few segments of the genomes in which each cluster included both chimpanzees and humans; in those regions, some humans were more closely related to some chimpanzees than to other humans.

"Instances in which natural selection maintains genetic variation in a population over millions of years are thought to be extremely rare," the authors wrote. The oldest and best known example of balanced polymorphism shared between humans and chimpanzees is the major histocompatibility complex (MHC), a group of genes that help the immune system distinguish between the body and potential invaders, such as bacteria or viruses.

Last year, a team led by Przeworski found that humans and gibbons shared genetic variation related to the ABO blood-group system from a common ancestor.

The six new examples of balanced selection described in this study appear to play a role, like the MHC, in fending off infectious disease. This requires a variety of evolutionary tools, including balancing selection. When a population moves to a new environment -- for example the exodus out of Africa to northern Europe -- they face many one-time adjustments, such as adapting to less intense sunlight and decreased ultraviolet radiation. Over many generations, their offspring manage to decrease melanin production -- a static adaptation for a static environment.

Fighting off pathogens is more dynamic, a constant arms race. Balancing selection may have enabled humans and chimps to retain multiple lines of defense that can be called on when a pathogen evolves new weapons.

"Our results imply that dynamic co-evolution of human hosts and their pathogens has played an important role in shaping human variation," Przeworski said. "This highlights the importance of a different kind of selection pressure in human evolution."

The National Institutes of Health, The Royal Society, the Wellcome Trust and the Howard Hughes Medical Institute funded this study. Additional authors include Ziyue Gao, Laure Segurel and Guy Sella from the University of Chicago; Susanne Pfeifer, Adam Auton, Oliver Venn, Rory Bowden, Peter Donnelly and Gilean McVean from Oxford University; Ronald Bonstrop from the Biomedical Primate Research Centre in the Netherlands; and Jeffrey Wall from the University of California at San Francisco.


Story Source:

The above story is based on materials provided by University of Chicago Medical Center. Note: Materials may be edited for content and length.


Journal Reference:

  1. E. M. Leffler, Z. Gao, S. Pfeifer, L. Segurel, A. Auton, O. Venn, R. Bowden, R. Bontrop, J. D. Wall, G. Sella, P. Donnelly, G. McVean, M. Przeworski. Multiple Instances of Ancient Balancing Selection Shared Between Humans and Chimpanzees. Science, 2013; DOI: 10.1126/science.1234070

Cite This Page:

University of Chicago Medical Center. "Humans and chimps share genetic strategy in battle against pathogens." ScienceDaily. ScienceDaily, 14 February 2013. <www.sciencedaily.com/releases/2013/02/130214141608.htm>.
University of Chicago Medical Center. (2013, February 14). Humans and chimps share genetic strategy in battle against pathogens. ScienceDaily. Retrieved August 1, 2014 from www.sciencedaily.com/releases/2013/02/130214141608.htm
University of Chicago Medical Center. "Humans and chimps share genetic strategy in battle against pathogens." ScienceDaily. www.sciencedaily.com/releases/2013/02/130214141608.htm (accessed August 1, 2014).

Share This




More Fossils & Ruins News

Friday, August 1, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Where Did The World Trade Center Shipwreck Come From?

Where Did The World Trade Center Shipwreck Come From?

Newsy (July 31, 2014) Scientists say a ship remnant discovered underneath Ground Zero dates back to the 18th century. Why it sank is still uncertain. Video provided by Newsy
Powered by NewsLook.com
Rodents Rampant in Gardens Around Louvre

Rodents Rampant in Gardens Around Louvre

AP (July 29, 2014) Food scraps and other items left on the grounds by picnickers brings unwelcome visitors to the grounds of the world famous and popular Louvre Museum in Paris. (July 29) Video provided by AP
Powered by NewsLook.com
London's Famed 'Gherkin' Goes on Sale for 650 Mln

London's Famed 'Gherkin' Goes on Sale for 650 Mln

AFP (July 29, 2014) London's "Gherkin" office tower, one of the landmarks on the British capital's skyline, went on sale for about 650 million ($1.1 billion, 820 million euros) on Tuesday after being placed into receivership. Duration: 00:36 Video provided by AFP
Powered by NewsLook.com
Asteroid's Timing Was 'Colossal Bad Luck' For The Dinosaurs

Asteroid's Timing Was 'Colossal Bad Luck' For The Dinosaurs

Newsy (July 28, 2014) The asteroid that killed the dinosaurs struck at the worst time for them. A new study says that if it hit earlier or later, they might've survived. 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:
from the past week

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