It wasn’t that long ago that scientists didn’t think animals could rival humans in terms of intelligence, emotions, or empathy. But the groundbreaking work of Dr. Frans de Waal helped change all of that. De Waal spent his life studying the lives of animals — especially our closest cousins, chimpanzees and bonobos.The primatologist died last week at the age of 75, and we wanted to remember him by sharing one of our favorite conversations with him on the show. It’s from 2019, when he published his book Mama’s Last Hug: Animal Emotions and What They Tell Us About Ourselves.In it, he tells the story of a female chimp who didn’t produce enough milk to feed her young. When de Waal taught her to feed her baby with a bottle instead, she repaid him with what most of us would recognize as gratitude: holding both of his hands, and whimpering sadly if he tried to leave.Transcripts for each segment will be available the week after the show airs on sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.