DNA helix DNA helix Pioneering research out of Israel reveals more about how DNA turns on and off. (Photo: Andrea Laurel/Flickr)

Human evolution reveals clue to solving modern illnesses

An 'on/off switch' in the brain could help with Alzheimer's and other conditions.

What separates modern-day humans from the Neanderthals that came before us, and why do today's humans experience neurological conditions such as Alzheimer's disease? According to research conducted at the Hebrew University of Jerusalem and published in the journal Science, the answer lies in the genes.

It turns out that humans (Homo sapiens) and Neanderthals (Homo neanderthalensis) shared 99.84 percent of the same DNA. Why, then, were the two species so different? Like all species, not every piece of DNA that we carry in our genetic code is active. Some of the DNA is active, while some DNA carries genetic instructions that are not used by the body (or by an entire species). This non-active DNA is effectively turned off and lies dormant while the active DNA produces the physical attributes that define a species.

The new research reveals more about this: a cluster of genes called HOXD was turned off in Neanderthals and another Stone Age hominid species called the Denisovans. This cluster of five genes determines the shape and size of a human's limbs, including the arms and hands. The fact that the genes were off in the Neanderthal may be an indication of why they had shorter legs and arms and larger hands and fingers than modern humans, as well as other morphological differences.

Lead researcher Liran Carmel, a geneticist, told Reuters that this discovery has much more potential than understanding limb size. He said the HOXD genes cluster may have also had an effect on the brain. Further understanding of this could reveal how to turn on or off neurological diseases of the brain such as Alzheimer's. That's because a majority of the genes being on or off were related to neurological and neuropsychiatric disorders such as Alzheimer's.

This is just the latest revelation about genetic switches and evolution. Last year a study by researchers at Cornell University in New York found that the evolutionary divergence of humans and chimpanzees that occurred between 4 and 6 million years ago was influenced by mutations to DNA sequences that turn genes on and off.

There's still a long way to go in this research, but this may be one more piece of the puzzle that must be solved to better understand human neurological conditions and how to prevent them in the future.

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