What behavioral effect may have occurred as humans began to select for tameness?

A. Dogs became more independent.

B. Dogs lost their instinct to live in packs.

C. Dogs no longer worked in cooperative groups.

D. Dogs became more eager to form social relations with humans.

The correct option is D.

As a result of tameness, dog became more eager to form social relations with humans. Due to the years of relation between dogs and humans, dogs have acquire the capacity to understand and communicate with humans; this represent a form of physical and social evolution of dogs.