When the baby gorillas Massabi and Koto were captured by hunters 11 years ago, few would have given much for their chances of returning to the wilderness.
With their habitats ravaged by deforestation, conflict, mining and the animal trade, the world's great apes are under a relentless assault which has seen their numbers dwindle from millions to as few as 350,000.
But Massabi and Koto are proof that, at least in one place, the slide towards extinction is being reversed.
It was announced yesterday that the two apes have become only the second and third gorillas ever to be reintroduced to the wild and produce offspring.
The new mothers gave birth approximately 10 days apart in the Lefini reserve in the Republic of Congo, where they have been carefully restored to their natural habitat in a unique project by Britain's John Aspinall Foundation.
The two orphaned gorillas, who were confiscated from their captors before they could be sold to foreign collectors, are among a group of 45 of the primates that have been reintroduced to protected reserves in the Congo and Gabon.
Amos Courage, the director of the project, said: "This is enormously important symbolically. These two orphans have been reintroduced in an area that had a good population of gorillas in the 1950s. That population was almost hunted to extinction. Now we have two mothers who were themselves orphans and have been able to breed in the region they once inhabited.
"These are not huge numbers, but they get across a very important message that the great apes are coming back to areas that once were theirs."
An international treaty providing the first comprehensive strategy to save the world's great apes was signed last year by the 23 states with primate populations and a group of donor countries, led by Britain.
The deal, billed as the last chance to save humanity's nearest relatives, set the target of significantly slowing the loss of great apes and their habitat by 2010 and securing the future in the wild of all the species - including chimpanzees, orang-utans and bonobos, or pygmy chimpanzees - by 2015.
Experts have warned that unless there is urgent action, 90 per cent of the jungle and wilderness occupied by gorillas will suffer from incursions from human development over the next 25 years.
It is estimated that there are just 5,000 gorillas left in the Republic of Congo and its neighbour, the Democratic Republic of Congo.
The slow journey of Massabi, who is now 13, and Koto, who is 11, from the cages of the hunters back to Lefini began when they were found by the Congolese authorities at a port waiting to be placed on a boat and shipped abroad to private collectors.
They were handed over to the John Aspinall Foundation, named after the 1960s playboy turned eccentric zoo-keeper and conservationist. The organisation has set up the only projects in the world where captive primates are returned to their natural habitat.
Often the apes are orphans whose mothers have been butchered for the bushmeat trade and the babies kept to be sold on as exotic pets. So far, the foundation has reintroduced 45 great apes. They include six "second-generation" gorillas which were born in Howletts, Aspinall's private zoo in Kent, and successfully reintroduced into the wild in Gabon in 2003.
The project in Lefini, situated to the north of the Congolese capital, Brazzaville, slowly reintegrates orphaned and captive gorillas back into wild family groups. The vast reserve, extending over 250,000 acres, boasted a dense population of lowland gorillas until the 1950s. But their numbers dwindled in the face of hunting and illegal logging, until the area was declared a protected reserve 15 years ago.
Massabi and Koto, who have been cared for by the foundation for eight years, are now part of a group of four male and five female gorillas which roam in the reserve's equatorial jungle.
Monitors from the foundation, who maintain a careful watch on the group, discovered them carrying their babies this month and are optimistic they will survive. A third female in the same group may also be pregnant.
The continued success of the programme, which had its first live birth in 2003, will depend on persuading the offspring of gorillas such as Massabi and Koto to be more wary of their human guardians.
Mr Courage said: "At the moment, the gorillas are very used to us and unperturbed by our presence. We want the next generation, like the babies that have been born, to be more stand-offish. They need to re-learn to fear humans."
The world of the gorilla
Lowland gorillas are endangered, but they remain far more common than their relatives, the mountain gorillas. They live in dense rainforests, and it is difficult for scientists to accurately estimate how many survive in Cameroon, Central African Republic, Congo, Equatorial Guinea, Gabon, Angola, and the Democratic Republic of Congo. Lowland gorillas tend to be smaller, with shorter hair and longer arms. Gorillas can climb trees, but are usually found on the ground in communities of up to 30. These troops are organised into fascinating social structures. They are led by one dominant, older adult male, often called a silverback because of the swath of silver hair that adorns his otherwise dark fur.
* Type: Mammal
* Diet: Omnivore
* Average lifespan in the wild: 35 years
* Size: Standing height 4ft to 6ft (1.2m to 1.8m)
* Weight: 150lb to 400lb (68kg to 181 kg)