Fast-Mutating DNA Sequences Reveal What it Means to be Human

DNA and our genetic code define what it means to be human. Deciphering this code, though, is more difficult than you might think. Now, scientists have discovered how the activation of specific stretches of DNA control the development of uniquely human characteristics, revealing a bit more about the evolution of our species.

In order to learn a little bit more about our genetic code, the researchers used the latest sequencing and bioinformatics tools in order to find genomic regions that guide the development of human-specific characteristics. These results offer new clues as to how the activation of similar stretches of DNA can sometimes result in vastly different outcomes.

In fact, the researchers discovered stretches of DNA that evolved much more quickly than others. These fast-evolving stretches could have been crucial to our ancestors when they first became distinct from our closest primate relatives. Known as human accelerated regions, or HARs, these stretches don't seem to encode specific genes. The researchers believe that, instead, HARs act as "enhancers," controlling when and for how long certain genes are switched on during embryonic development.

Using embryonic animal models combined with powerful computational genomics analysis, the researchers identified more than 2,600 HARs in all. They weren't done yet, though. The scientists then created a program called EnhancerFinders in order to whittle the list down to the HARs that were the most likely to be enhancers.

In the end, the researchers discovered five HARs which were active in both human and chimpanzees genomes. These HARs seemed to enhance patterns of gene activation that were uniquely human. The human versions of these HARs were active in a region of the brain between the midbrain and hindbrain while the chimp versions were not.

"These results, while preliminary, offer an unprecedented glimpse into how very recent changes to the human genome have modified the genetic programs that control embryonic development to potentially yield different results," said Tony Capra, one of the researchers, in a news release. "We anticipate that if we were to look at the activity of HARs that are enhancers during later developmental stages, we would see even more differences between humans and chimpanzees."

The findings reveal a little bit more about the evolution of humans and their relation with chimps. As scientists continue to look at these HARs, though, they may come closer to the answer to the questions about exactly what makes us human.

The findings are published in the journal Philosophical Transations of The Royal Society B.