Human Accelerated Region 1 (HAR1) is a segment of the human genome that evolved rapidly after humans diverged from chimpanzees. Located on chromosome 20, HAR1 was identified in 2006 when researchers discovered 49 regions of the human genome that differ significantly from our closest primate ancestors. These regions are called human accelerated regions (HARs).

HAR1 contains two long non-coding RNA genes, HAR1A and HAR1B. HAR1A is expressed in Cajal-Retzius cells during brain development, specifically between the 7th and 18th gestational weeks. Research shows it is active in the dorsal telencephalon of fetuses and remains present in the adult cerebellum and forebrain. Scientists found evidence that REST proteins repress HAR1 in individuals with Huntington's disease, potentially contributing to neurodegeneration.

The RNA structure of HAR1A has proven distinct from other mammals—adopting a different fold compared to the chimpanzee sequence. Many HARs are associated with genes involved in neurodevelopment, making this region particularly significant for understanding what makes human brains unique. The discovery emerged from comparative genomics studies examining evolutionary conservation across species.