Evolutionary theory predicts that individuals adapt to the living conditions faced during their lifespan. From the start of the Taï Chimpanzee Project, the foremost question was how living in a dense rainforest affects the behaviour patterns compared to the Gombe and Mahale chimpanzees, which lived in a more open environment dominated by mosaic habitat with dry woodland savanna patches and some gallery forest. Do Taï chimpanzees need a precise mental map to find their food in this dense rainforest? How does the more social nature of the social life of the Taï chimpanzees affect paternity in this population? How old is tool use, exemplified by the stone hammers used to crack nuts in Taï? Where do females come from and where are they going when they transfer between communities as young adults? Is there a difference in the cooperation level between populations when hunting arboreal monkeys and why? In all these domains, the Taï Chimpanzee Project presented new data and replicated them over different periods of time and different social groups. The role of the environment for each of this domain was discussed and proved to be essential in explaining population differences.