Actually I believe the more reasonable or pertinent question is why are we so much different from apes and other animals. The similarities between man and ape are primarily physical, in almost every other important way we're very much different. In my opinion, this is the greatest challenge evolution faces. Science, specifically evolution, can't adequately explain the uniqueness of humans compared to all animals, not just apes. I also believe as a TE it is the single biggest challenge they must accurately account for. I have yet to hear any sort of evolutionary explanation that can adequately explain the human soul and spirit. Creation, through God's Word, certainly does!
Dolphins are more intelligent that most other groups of mammals also, does that mean we also descended from them? Whether one group of animals is smarter than another makes no difference, none can come close to comparing to the intelligence of human beings. This is why we are unique and made in the image of God.