Humans possess unique traits that distinguish them from their closest animal relatives, such as chimpanzees and bonobos, and at least some of these traits could be linked to what scientists call human accelerated regions (HARs). HARs are specific regions of DNA that evolved rapidly in humans, and scientists believe they could be behind the qualities that set humans apart.
In a recent study, scientists from the Gladstone Institute of Data Science and Biotechnology found that the 3D folding of human DNA in the nucleus was a key factor in the evolution of HARs. They discovered that the structural changes in human DNA and its altered 3D folding led to genes within HARs being "hijacked," linking them to different protein-coding genes than originally applied. Many genes within HARs act as enhancers that increase the transcription of their linked genes, and they can impact the activity of any gene that ends up close by, which can vary depending on how DNA is folded.
The team compared the genomes of 241 mammal species using machine learning to identify 312 HARs and examined where they were located within the 3D neighbourhoods of folded DNA. They found that almost 30 per cent of HARs were in the regions of DNA where structural variations had caused the genome to fold differently in humans compared to other primates.
They also discovered that neighbourhoods containing HARs were rich with the genes that differentiate humans from chimpanzees. In an experiment that compared DNA within growing human and chimpanzee stem cells, one-third of identified HARs were transcribed specifically during the development of the human neocortex. Many HARs play a role in embryo development, especially in forming neural pathways associated with intelligence, reading, social skills, memory, attention, and focus – traits distinctly different in humans than in other animals.