Human brain is different from other mammalian brains, both anatomically and functionally. One of the anatomical hallmarks that distinguishes human brains from those of other mammalian species is an expansion of the size of the brain, especially the cerebral cortex. Such expansion of the cerebral cortex is thought to be generated by changes in a pattern of neurogenesis during development. What controls the unique pattern of neurogenesis in human brain development and how was this feature acquired during evolution? In this lecture, I will discuss studies that investigated possible cellular and genetic mechanisms that might underlie human-specific changes of cortical development, with a focus on a paper that generated a “humanized” mouse brain.