Fiona Rogers / Eastern chimpanzee (Pan troglodytes schweinfurtheii) infant male 'Gizmo' aged 2 years, portrait. Gombe National Park, Tanzania.

Anup Shah / Eastern chimpanzee (Pan troglodytes schweinfurtheii) adult male 'Frodo' aged 35 years portrait. Gombe National Park, Tanzania.

Mark Bowler / Red howler monkey (Alouatta seniculus) howling, captive, digitally modified

Edwin Giesbers / Western lowland gorilla, (Gorilla gorilla gorilla) with finger on chin, captive, occurs in Central Africa. Critically endangered.

Enrique Lopez-Tapia / Arbore man smiling, with traditional clothes. Lower Omo Valley. Ethiopia, November 2014

Fiona Rogers / Eastern chimpanzee (Pan troglodytes schweinfurtheii) male baby 'Gizmo' aged 1-2 years portrait. Gombe National Park, Tanzania.

Mark Taylor / Bulldog puppy with chin on paws, against white background

Cyril Ruoso / Orangutan (Pongo pygmaeus) close-up portrait of any adult resting chin in hand, Kalimantan, Indonesia

Diane McAllister / Japanese Macaque (Macaca fuscata) positioned on the edge of the hot springs with head on rock, paw under chin, staring, Jigokudani, Japan, January

Mark Moffett / Giant Panda (Ailuropoda melanoleuca) using thumb to eat bamboo, Wolong Nature Reserve, China Conservation and Research Center for the Giant Panda, China

David Hall / Diver extending his hand towards a Harbor seal (Phoca vitulina) which touched the diver's glove with its chin, Croker Rock, Queen Charlotte Strait, British Columbia, Canada. September. No model re...