A dream come true
I had dreamed of finding a study site like this: a dense population of orang-utans in an area where we could follow them wherever they roamed - where we might finally unravel the truth about the orang's mysterious social life.
In the forests of Suaq Balimbing in Sumatra, we had discovered that the orang-utan density was off the chart - more than 10 individuals per square kilometre - at least double that ever recorded elsewhere.
Then, to top it all, one of the team casually mentioned that he had seen an orang-utan female poke a stick into a tree-hole. This kind of tool-use had never been seen in wild orang-utans! We had to stay.
Different tools for different tasks
Five years on, we have seen hundreds of instances of orang-utans making and using different tools made from branches for different occasions - extracting honey from bees' nests, 'fishing' for termites by poking twigs into tree-hole nests and extricating the fatty seeds from well-protected Neesia fruits.
In zoos, the red ape is a highly technical and sociable creature - youngsters play-wrestle, adults have a huge appetite for sex, and are infinitely tolerant of insolent youngsters stealing their food. Captive orang-utans spend hours examining anything within reach and they are true escape artists, able to get out of the most solidly constructed cage. Yet in its natural forest home, the orang-utan is, the textbooks say, an unskilled recluse.
So why are the Suaq orang-utans technologically sophisticated? The answer came to us when we looked at their social life, which was more like that of their gregarious zoo cousins than had ever been seen before. Part of the reason for this was that, because of the unusually high productivity of the forest, there were so many orang-utans in Suaq and they just couldn't help bumping into each other.
They actively sought each other's company, travelling from tree to tree together and even sharing food. Mating associations lasted much longer than elsewhere, and new mothers often fed and travelled together, usually accompanied by their older, independent youngsters, who played vigorously among themselves.
We realised that all this social contact could account for the widespread tool use. When animals regularly interact, new, beneficial behaviour - such as tool-use - can spread rapidly once it has been invented.
A fragile culture
So an animal's environment and its mental abilities merely set the scene. Any new technique will only catch on once a threshold of relaxed social contact is reached and maintained. This underscores the fragility of culture and technology. Once a culture has gone extinct, it may be lost forever. Reduced habitat quality as a result of selective logging may already be enough to send the orang-utans back to the hominoid equivalent of the Dark Ages.
From an original article in the November 1998 issue of BBC Wildlife Magazine - Out of the dark ages.