What did a 184kg gorilla do when he escaped his London zoo enclosure? The silverback guzzled 5l of undiluted blackcurrant squash before being sedated and put back in his cell. It might be behaviour worthy of an unruly toddler, but primates fascinate us. Another of our evolutionary forebears, an orang-utan, stole the headlines this week after being snapped hunting for figs in the jungle of Borneo.I've been to that jungle and seen orang-utans on a boat trip in Kalimantan (Indonesian Borneo). The orang-utans lived in a semi-wild state in a national park, studied and fed fruit by scientists led by Biruté Mary Galdikas.On their feeding platform, the leading male, a complacent, obese creature, would scoff his fill first until he was almost comatose, then heave himself up into the canopy and digest, like an ageing uncle after Christmas lunch.During the sunset boat ride back, I looked up into the trees and was astonished to find them filled with dozens of monkeys. They weren't chattering and fighting, but sitting peacefully on branches overlooking the water, their tails hanging below them as they gazed into the dusk.Monkeys, we were told this week, can produce stone tools that archaeologists had, until now, always credited exclusively to humans. The monkeys don't actually use the tools, but make them as a by-product of smashing rocks whose dust they like to eat. This human-like behaviour by primates has thrown into doubt widely accepted tenets of evolutionary science.Some years ago, geneticists at the Harvard/MIT Broad Institute discovered DNA evidence suggesting human and chimp ancestors might have interbred for thousands of years. This challenged the idea that humans and chimps split off from each other cleanly on different evolutionary tracks.Another genetic study by the same scientists further challenged our idea of Homo sapiens as uniquely clever beasts. The data suggested that, after moving out of Africa and coming across Neanderthals, humans had interbred with them too. And there's a growing body of evidence that Neanderthals weren't the dumb, grunting creatures of Hollywood lore, but were capable of conceptual thought and possibly even religious rituals involving mysterious piles of stalactites.Our surprise at these discoveries just goes to show how attached we are to the myths of creationism, even if we think we're modern. We keep searching for that moment, that line in the sand, when humans stopped being animals and became instead that special creature made in God's image. Was it when we finally stood fully upright and donned loincloths? Was it when we invented sponge cake?Or perhaps evolution isn't a linear story, but a chaotic process full of dead-ends, switchbacks and lulls, arriving at the modern juice-swilling gorilla and his cousin, the juice-guzzling toddler.Humans are unique, of course, but only in being a particularly advanced breed of animal. It's helpful to remember that when I witness the strange, imitative mating rituals of the flirting couple, the chest-thrusting postures of the presidential candidate or the vicious squabbling of young children. The wonder is not how far we've come. The wonder is how savage we still are. ..