New clues in difference in humans, chimps

April 20, 2009 6:48:36 PM PDT
Researchers in the Bay Area are uncovering new clues about what makes humans human. The project involves the use of massive computer power to compare our DNA with that of our closest relative in nature, the chimpanzee.

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If one watches long enough, it can be a little unnerving just how closely chimpanzees resemble humans. They should; their DNA blueprint is 99 percent identical to ours.

"So, we're much more similar to a chimp than a rat is to a mouse," says Katherine Pollard.

Pollard should know. Working at the Gladstone Institute at UCSF, the bio-statistician is on a mission to decipher the 1 percent difference in our genome that makes humans human.

"Well, it sounds close, only 1 percent. But, you have to remember the genome is 3 billion base pairs long. So, 1 percent of 3 billion, we're still talking about millions of letters that are different," she explained.

To find them she wrote a special program and fed it into a massively powerful computer cluster. The software scans the genome for sequences found in humans, but not chimps or other animals. Katey estimates the process would take about 35 years on a laptop.

But, within a few months she hit genetic pay dirt.

"This is the region that I found. This is HAR-1 and here's the sequence," she showed ABC7.

HAR stands for Human Accelerated Region. They are patches of uniquely-human code found in a section of the genome that tends to be heavily influenced by natural selection. Scientists theorize that when we diverged from our common ancestor, changes in those sequences accelerated, producing key differences.

"In the list of regions I identified there really is an enrichment for sequences involving the brain and development of the brain. But, there're also some other really important parts about our biology that have gotten hit. Things about our diet, how we digest and metabolize food are really different than non-human primates," Pollard explained.

Speech is another area. A sequence called FOXP2 may help give humans the delicate muscle control in their faces to produce words far more complex than animal sounds. And, the evolution from leathery paws into sensitive hands that build computers may be the result of yet another sequence dubbed HAR-2.

"It's a sequence that sends message. It says to turn on gene expression during development at the stage when an embryo is starting to develop its forearms and its hands," Pollard said.

She believes researchers may someday be able to tweak key genes for medical benefit, possibly giving humans the same natural resistance to HIV that chimpanzees have. But, in the meantime, humans may simply have to take comfort in the knowledge that one percent is still a pretty big difference.

Research already extends beyond the lab. A team in England is studying subjects who have a rare, mutated version of one of the sequences, FOXP2. Those patients have normal brain and cognitive function but are not able to create the facial movements needed for speech.

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