Hasani's mother, Monifa, abandoned the newborn shortly after giving birth.
Monifa was a first-time mom, and although she'd shown all the right instincts during the pregnancy, she was immediately disinterested in her new baby. She checked him occasionally in the first hours, but refused to hold him or feed him.
Zookeepers quickly checked to make sure Hasani was healthy then returned him to his nest. They tried to interest Monifa in her newborn, but it just didn't take.
"She just kept going as far away from him as possible. She really showed no nurturing instincts," said Corinne MacDonald, curator of primates at the zoo.
After nearly three days of watching the scene play out on Web cams installed in the gorilla facility, the zookeepers and vets made a decision to remove Hasani and hand rear him.
"We don't know why, or if this rejection happens in the wild because witnessing a gorilla birth is so rare, but it does happen in zoos," said Edwards.
For months the staff fed, nurtured and played with Hasani 24 hours a day. He was healthy and seemingly happy. But the goal from the beginning was to reintroduce the baby to his gorilla family.
But that introduction mandated an ambassador for the baby, another gorilla who would protect and care for Hasani. Gorilla surrogacy has been accomplished at other zoos across the world, but it's always a tenuous experiment.
"We worried, but we had plans in place for all the possible scenarios," says MacDonald.
The first task was to identify a mother candidate among the zoo gorillas. But for the staff at the San Francisco Zoo, the obvious choice was 27 year-old Bawang.
"She was watching the birth and she was very interested from the very beginning, and she has also raised three offspring successfully," MacDonald said.
Hasani's care and rearing had occurred in a fenced off area within the gorilla facility, and once when he had received a vaccination it appeared to affect Bawang even from the other side of the room.
"He cried out in fear and she ran over to the wall of her enclosure and vocalized that she was concerned for him," said MacDonald. They had never been in physical contact, but Bawang showed the nurturing instincts that Monifa, Hasani's biological mom, had not.
The next step was the surrogate training. The San Francisco Zoo has amazing video of the process with great narration from the zookeepers.
At 4 months of age, the actual physical introduction of Hasani and Bawang was a much anticipated event.
"I had such a strong feeling that Bawang would care for the baby, but there's always worry and we had to supervise them very closely in case there were any signs of aggression," MacDonald said.
The video of the first meeting is incredibly touching. It went slowly; Bawang let everything happen on Hasani's terms.
When Hasani made a tentative move to interact with Bawang, she picked him up and started to snuggle him. They played, they cuddled and they fed together.
"I think every mother out there can appreciate what Bawang did," MacDonald said.