Brain size in modern humans is also only weakly correlated with intelligence [1]. So they might not even have been stupid due to their smaller brain size. Sper

Brain size in modern humans is also only weakly correlated with intelligence [1]. So they might not even have been stupid due to their smaller brain size. Sperm whales don't have much of a chance to manipulate their environment, but they have the largest brains on earth [2]. [1] https://www.scientificamerican.com/article/does-brain-size-matter1/#:~:text=In%20healthy%20volunteers%2C%20total%20brain,overall%20variability%20in%20general%20intelligence https://www.scientificamerican.com/article/does-brain-size-m.... [2] https://www.amnh.org/exhibitions/extreme-mammals/extreme-bodies/brains#:~:text=The%20sperm%20whale%20has%20the,(7%20to%209%20kilograms) https://www.amnh.org/exhibitions/extreme-mammals/extreme-bod....