The genetic difference between humans and chimpanzees is about 0.1%, on average. Although this huge genetic similarity, the differences between humans and chimpanzees can be attributed to how these genes are regulated. The same genes are expressed in the same brain regions in human, chimp, and gorilla, but in different amounts. Thousands of differences like these affect brain development and function and help explain why the human brain is larger and smarter. There is also a slight difference in genes (the 0.1% difference) which could seem small but has a big difference.