The more you look, the more similarities between humans and other apes there are.
The idea De Waal champions that humanity has “two inner apes” – the aggressive chimp and the peaceful bonobo – may well help us think about what’s going on, but only to a limited extent. Humans are neither chimps nor bonobos.
Similarly, Grandin’s conclusion that “De Waal's most hopeful message is that peaceful behavior can be learned” looks just great; but – strictly from the evidence cited – that conclusion can only be applied to juvenile rhesus and stumptail monkeys in the study.
There may well be evidence from historical, political, cultural and other studies of humans that peaceful behaviour can be learned, but one should be cautious about a “message” from even the most careful study of other animals.