If you want to read an accessible book on the evolution of human intelligence and how to understand animal intelligence as a result read Carl Sagan's Dragons of Eden. Its a little dated now but it, like everything Sagan did, is grounded deeply in the philosophical and spiritual as well as the scientific.
One interesting passage talks about the abilities for chimpanzees to learn sign language (as was a popular experiment at the time). He explains that in some cases juvenile chimpanzees have learnt 100 words - equivalent to 1/10th of 'basic English'. He postulates that, given a fully devised rational education program, its possible to teach a chimpanzee full 'basic English' (along with the true understanding that comes with that) by the time its an adult. Furthermore, if taught, its possible a chimpanzee culture could develop in a particular group and over time artificial evolution would lead to them becoming excellent communicators. Food for thought.