Part of that evolution involved the loss of a prehensile tale as well as a relative loss of strength. So, it's not clear that humans are any more "complex" than their primate ancestors.
Can you name a creature that has de-volved??? Is de-evolution the norm??
There is no such thing as "de-evolution." However, there are plenty of examples of species that have lost certain abilities and/or traits as they have evolved to adapt to their environment. Penguins can't fly. Land-dwelling animals have lost the ability to breathe in water. Hooved animals have seen their fingers and toes merge into one structure. Whales have lost the use of their legs. Fish that live in caves or in the deep oceans have lost the ability to see. Ants, as descendants of wasps, have mostly lost the ability to fly. The list goes on and on.
Most parasites.