If they handed out prizes for gurning, then this lot would swing to the top of the queue.
These intimate portraits of Bonobos, gorillas and orangutans are part of a project by German photographer Volker Gutgessell who has spent the last four years visiting Frankfurt Zoo.
Standing patiently for several hours a day, 58-year-old Mr Volker has become a master at capturing the behaviours and expressions of his subjects.

Pensive primate: A Bonobo at Frankfurt Zoo is captured on camera looking lost in thought

Mr Volker said: 'I stand for many hours watching both the apes and the families that visit them. I see the way the parent chimps and gorillas treat their children.
'In all the years I've visited them, I've never seen an ape parent hit its child.'
One of the photographer's most remarkable images shows a Bonobo mother gently cradling her child.

Gawker: A chimp is captured looking startled as part of photographer Volker Gutgessell's four-year project

Another hilarious shot shows one of the naughty baby monkeys mocking an elder by baring its top teeth.
Mr Volker said: 'They are so cute with them and have endless patience - even though the little ones can be naughty sometimes.
'The human parents I see visiting the apes can actually learn a lot from them.'

Smacker: A touching show of affection between two of the creatures

Mr Volker used to travel the world as a media manager until he slipped a disc and was left with chronic back pain in 2004. Then in 2007, Volker developed tinnitus as a result of his injury, causing a constant ringing in his ears.
As Volker cannot hear, he feels a special connection to the primates through visual communication - picking up on the body language of his ape 'models' while shooting them.
Volker said: 'The more you watch them, the more similarities you see between us and them. Their movement is so strikingly similar to ours it becomes quite easy to read what's going on.

Chewing it over: A monkey at Frankfurt Zoo looks lost in his own thoughts

'Eye contact is very important - sometimes they see into the camera lens and become transfixed. The bonobos are funny creatures - they're my favourite.
'They live in a society where the males are ruled by the females. So you see the males trying desperately to socialise as much as possible by preening the females - they can't do enough for them!'
Although his photographs are intended to amuse, there is a serious message behind Mr Volker's work.
My urgent message is for us to learn from the gentle conduct of our animal relatives the primates,' he said.

Surprise me! A baby orangutan is caught off guard by the photographer

Don't look so sour: One adult primate appears unhappy about the interruption to snacktime

Let rip: An adult male gorilla makes himself heard at Frankfurt Zoo

Read more: Monkey see, monkey do: The remarkably human faces pulled by our primate cousins | Mail Online