What gave humans the ability to talk, a characteristic not found in apes.
The short answer: We needed to be able to gossip.
The long answer: Early hominids leaving the forest found themselves in a unique situation in which cooperation among themselves in novel ways gave them a special evolutionary advantage. To do this they needed to communicate, and so they evolved complex facial expressions and voice sounds. As time went on, and communications needed to be more complex, combinations of sounds were the most effective means of doing so.
Why don't all the other animals talk? Most animals do have some basic means of communicating by voice, but nothing nearly as complex as what humans do. Hominids did this at great price. Early on they gave up much of their sense of smell so they could concentrate more brainpower to the difficult task of understanding each other. That led to bigger and bigger brains, but hominids were limited by the size of the head that could pass through the birth canal. So they evolved the novel solution that the brain continued to grow after birth. That's cool, but as a result, babies are very helpless for several years after birth. That required a lot of resources to feed and care for helpless babies, and it required mothers to get commitment from others in the species. Hominids were able to do that. All that patience in caring for babies led to the smartest creatures on earth, creatures that were able to talk and understand each other, creatures that were able to work together to find new ways to get food and protect themselves, creatures that could develop deep relationships based on mutual trust.
Which brings me back to my original point. Hominids needed deep trusting relationships, and to do that they needed to know whom they could trust. There is no better method to find out who will stab you when your back is turned but to gossip. And so hominids spent long hours around the fire in the evenings, telling stories about who did what. And from that, they learned who they could trust, and developed deep relationships with those they selected, and that allowed them to build the communities necessary to grow helpless babies into adults with big brains.
So we learned to talk so we could gossip and commit to each other and grow babies into adults with big brains.