Reconstructing human-specific regulatory functions in model systems.

Uniquely human physical traits, such as an expanded cerebral cortex and changes in limb morphology that allow us to use tools and walk upright, are in part due to human-specific genetic changes that altered when, where, and how genes are expressed during development. Over 20 000 putative regulatory elements with potential human-specific functions have been discovered. Understanding how these elements contributed to human evolution requires identifying candidates most likely to have shaped human traits, then studying them in genetically modified animal models. Here, we review the progress and challenges in generating and studying such models and propose a pathway for advancing the field. Finally, we highlight that large-scale collaborations across multiple research domains are essential to decipher what makes us human.