Quite an interesting question i must say. As the evolution process has observed over the period of centuries, in the same species some creatures inherits the way of living and follows them for the rest of the life. However some others goes out of the box to fight for their existence, often affected by the surroundings.
For example, in human kind there are people who look for physical research data to believe the fact, lets call them H1, where others, H2 kind, accepts it as they were told so by some person or people they are influenced by. Humans who look out for research and data tend to use their brain more than the one's who just accepts the fact. As evolution process suggests, evolution and growth of mind in H1 will be more obvious then H2. It works and has worked the same way during the entire process of evolution from Amoeba to Humans and so will it continue to. In the end, if H2 are able to survive, they will be as they are today where H1's brain will evolve and grow to a better one.
This is the same way, why monkeys and apes are still around though humans have evolved from them.