Modern Diseases May Have Had Genetic Benefits for Ancient Human Ancestors

First Posted: Jan 29, 2015 09:54 AM EST
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Why do genetic diseases still exist after thousands of years? Scientists have taken a closer look at our ancient ancestors and have found that some modern maladies may have actually provided ancient benefits.

"Our research shows that some genetic features associated with psoriasis, Crohn's disease and other aspects of human health are ancient," said Omer Gokcumen, one of the researchers, in a news release.

Our early ancestors had telltale features, called deletions, while others did not. This actually mirrors the variations seen in modern humans. This genetic diversity may have arisen a million years ago or more in a common ancestor of humans.

In order to better understand these genetic differences and certain traits that may have made humans more susceptible to modern diseases, the researchers compared modern human genomes to those of other closely related species, including chimpanzees, Neanderthals and Denisovans. They identified chunks of DNA that exist in chimpanzees, but that were later erased through evolutionary processes. Called deletions, these DNA segments are present in some human genomes and missing in others.

In fact, the researchers found that certain functionally important deletions that vary among modern humans likely originated from a common ancestor of humans, Neanderthals and Denisovans. These old deletions include ones that are common in Crohn's disease and psioriasis patients, as well as deletions linked to a person's ability to respond to a number of drugs, including growth hormone treatments.

"Crohn's disease and psoriasis are damaging, but our findings suggest that there may be something else-some unknown factor now or in the past-that counteracts the danger when you carry genetic features that may increase susceptibility for these conditions," said Gokcumen. "Both diseases are autoimmune disorders, and one can imagine that in a pathogen-rich environment, a highly active immune system may actually be a good thing even if it increases the chances of an auto-immune response."

The findings reveal a bit more about why these modern diseases persist and weren't "weeded out" in the ancient past. In addition, it reveals that genetics have far more complicated interactions than you might think.

The findings are published in the journal Molecular Biology and Evolution.

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