In the Scottish archipelago of St. Kilda, sheep Sawai no visible enemies or predators, but probably they have all the makings to cope with the lack of food, severe weather conditions, which can kill polnaseleniya overnight and parasitic worms that live in their bodies and inhibit their immune system.
Despite all this, the breed of sheep continues to survive, and scientists are finally beginning to understand why. The presence of a strong immune system of some sheep and other high reproductive rates contribute to achieving such incredible stamina.
Some sheep Sawai have high levels of antibodies inherited from their parents, to help them survive in the presence of parasitic worms in the body and the cold weather. "Sheep with a strong immune system does not produce many offspring" - explained study researcher Andrea Greyhem, a biologist at Princeton University in New Jersey.
However, sheep with low levels of these immune antibodies raised more prone cold weather, produce more offspring. This finding explains why those other sheep instead of disappearing under the principles of natural selection are still present on the islands.
According to natural selection, sheep, which can not move hard winter weather conditions and actions parasites would have already vanished. But because they give birth each year of the twin lambs with all the attributes for survival, it still continues to exist.
Researchers have studied this type of sheep for the past 26 years, some researchers have even lived in the islands for many years. Sheep - a descendant of the sheep that existed during the Neolithic era. A previous study showed that the genus of sheep Sawai shrinking because of climate change.
Thousands of animals still living on the islands after their owners were evacuated by the Scottish Government in 1930 due to illness, poor harvests.
Greyhem travels to the island every August to collect blood samples from sheep and measure antibody levels in them. She said that information will help in the development of detailed biological explanation for why so different degree of immune protection in different people.
The relationship between the immune and reproductive performance in sheep could help explain the relation between the immune system and the ability to survival and fertility.
"This may help explain geterogenetiku in the human population," - added Greyhem.
Next, Greyhemi her colleagues hope that better understand the immunology sheep and be able to establish if the response of autoimmunity is the cause of death of sheep with high levels of antibodies in the body.
Original: LiveScience Translation: M. Potter