Discourse 5- Rationality

In part 5 of Discourse, D says that a majority of our biological processes can be explained by science, but our rationality cannot be explained by science. He says that since it cannot be explained, it must be a gift from God. He goes on to say that animals do not have intelligence and that animals do not use language to express themselves. I definitely disagree with D on this point. Given, in his defense, he wrote the Discourse years before any studies about animal behavior and language were done, but it has been prove many times that animals have their own language and use rationality for problem solving.