Sylvain Cordier / Gelada baboon (Theropithecus gelada) female carrying baby on back, dominant male in background. Debre Libanos, Rift Valley, Ethiopia.

Sylvain Cordier / Common Loon (Gavia immer) on lake carrying chick on back , Michigan, USA. June.

Morley Read / Slow motion clip of Leafcutter ants (Atta) carrying pieces of leaves back to their nest, Amazon rainforest, Napo Province, Ecuador.

Remi Masson / Eurasian beaver (Castor fiber) carrying branches back to lodge, dropping them when alarmed. River Rhone, Rhone-Alpes, France, June.

Brian Bevan / Close-up of a group of Wood ants (Formica rufa) carrying a dead insect back to their nest, Bedfordshire, England, UK, August.

Brian Bevan / Close-up of a group of Wood ants (Formica rufa) carrying a dead Common wasp (Vespula vulgaris) back to their nest, Bedfordshire, England, UK, August.

Marie Read / Eared grebes (Podiceps nigricollis), pair, one adult feeding one of two chicks riding on the other adult's back, Bowdoin National Wildlife Refuge, Montana, USA

Marie Read / Eared grebes (Podiceps nigricollis), pair, one adult carrying food (damselfly) for two chicks riding on the other adult's back, Bowdoin National Wildlife Refuge, Montana, USA

Marie Read / Eared grebes (Podiceps nigricollis), pair, one adult feeding chick riding on the other adult's back, Bowdoin National Wildlife Refuge, Montana, USA

Alex Hyde / Leaf-cutter ants (Atta cephalotes) carrying pieces of leaf that they have harvested back to their underground fungus garden in their nest, Osa Peninsula, Costa Rica. Photographed in mobile field studi...

Alex Hyde / Leaf-cutter ants (Atta cephalotes) carrying pieces of leaf that they have harvested back to their underground fungus garden in their nest, Osa Peninsula, Costa Rica. Photographed in mobile field studi...

Alex Hyde / Leaf-cutter ant (Atta cephalotes) carrying pieces of leaf that they have harvested back to their underground fungus garden in their nest, Osa Peninsula, Costa Rica

Bence Mate / Leaf cutter ants (Atta sp) silhouetted carrying plant matter, Laguna del Lagarto, Santa Rita, Costa Rica

Bence Mate / Leaf cutter ants (Atta sp) carrying plant matter, Costa Rica.

Suzi Eszterhas / Ring tailed lemur (Lemur catta) mothers with two-week babies. Berenty Private Reserve, Madagascar

Tony Heald / Asian elephant (Elephas maximus) domesticated elephant working, picking reeds, Kaziranga National Park, Assam, India, March 2009.

Pete Oxford / Nyshi man, Arunachal Pradesh, North East India, November 2014.

Cyril Ruoso / Woman with baby collecting Madagascar periwinkle (Catharanthus roseus) flowers and leaves, used in herbal medicine, and containing molecules which are used in the treatment of leukemia cancer. Berenty...

Cyril Ruoso / Woman with baby looking at Sisal (Agave sisalana) fibres drying for rope making, Berenty Reserve, Madagascar.

Krijn Trimbos / Great crested grebe (Podiceps cristatus) carrying chick on back, The Netherlands, May.

Danny Green / Japanese Macaque (Macaca fuscata) carrying young on back through snow, Nagano, Japan, February

Danny Green / Japanese Macaque (Macaca fuscata) carrying young on back through snow, Nagano, Japan, February

Bernard Castelein / Ring-tailed lemur (Lemur catta) female carrying two babies. Anjaha Community Conservation Site, near Ambalavao, Madagascar.

Konrad Wothe / Tracking shot of Leafcutter ants (Atta cephalotes) carrying bits of leaves back to their nest, Pucallpa, Huanuco Region, Peru.

Suzi Eszterhas / Koala (Phascolarctos cinereus) mother and joey aged sixth months, Queensland, Australia, captive.

Oliver Scholey / Grizzly bear (Ursus arctos horribilis) female with cub riding on back, Katmai National Park, Alaska, USA, August.

Ben Cranke / Wattled Jacana (Jacana jacana) perched on resting Capybara (Hydrochoerus hydrochaeris) Mato Grosso, Pantanal, Brazil. July.

Nick Garbutt / Infant Golden-crowned Sifaka (Propithecus tattersalli) on its mother's back. Forests adjacent to the village of Andranotsimaty, near Daraina, northern Madagascar. Critically endangered species.

Jabruson / Boy carrying bushmeat to market, Black-fronted Duiker (Cephalophus nigrifrons). Mbomo, Odzala-Kokoua National Park, Republic of Congo.

Enrique Lopez-Tapia / Tourists riding on domestic Indian elephant (Elephas maximus) crossing Narayani River in the dawn mist during wildlife safari, Royal Chitwan National Park, Nepal.

Enrique Lopez-Tapia / Tourists riding domesticated Indian Elephant (Elephas maximas) on safari, Royal Chitwan National Park, Nepal. October 2011.

Diane McAllister / Japanese Macaque (Macaca fuscata) juvenile riding on its mother's back, along snow trail in Jigokudani, Japan.

Andy Rouse / Verreaux Sifaka (Propithecus verreauxi) mother carrying baby. Madagascar

Andy Rouse / Verreaux Sifaka (Propithecus verreauxi) jumping across ground with baby on its back, Madagascar

Anup Shah,Anup Shah / Olive baboon (Papio cynocephalus anubis) female with infant on back, carrying away a gazelle carcass having taken it from a male. Masai Mara National Reserve, Kenya, July

Andy Rouse,Andy Rouse / Ring tailed Lemur (Lemur catta) mother carrying baby on back. Madagascar.

Fiona Rogers / Western lowland gorilla (Gorilla gorilla gorilla) infant 'Sopo' aged 18 months riding on his mother 'Mopambi's' back, Bai Hokou, Dzanga Sangha Special Dense Forest Reserve, Central African Republic. D...

Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) female 'Mopambi' carrying her infant 'Sopo' aged 18 months on her back crossing a river in Bai Hokou, Dzanga Sangha Special Dense Forest Reserve, Cent...

Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) female 'Mopambi' carrying her infant 'Sopo' aged 18 months on her back feeding on sedge grasses in Bai Hokou, Dzanga Sangha Special Dense Forest Reser...

Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) female 'Mopambi' carrying her infant 'Sopo' aged 18 months on her back walking through Bai Hokou, Dzanga Sangha Special Dense Forest Reserve, Central...

Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) female 'Mopambi' carrying her infant 'Sopo' aged 18 months on her back walking through Bai Hokou, Dzanga Sangha Special Dense Forest Reserve, Central...

Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) female 'Mopambi' carrying her infant 'Sopo' aged 18 months on her back walking through Bai Hokou, Dzanga Sangha Special Dense Forest Reserve, Central...

Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) female 'Mopambi' carrying her infant 'Sopo' aged 18 months on her back walking through Bai Hokou, Dzanga Sangha Special Dense Forest Reserve, Central...

Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) female 'Mopambi' carrying her infant 'Sopo' aged 18 months on her back walking through Bai Hokou, Dzanga Sangha Special Dense Forest Reserve, Central...

Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) female 'Malui' carrying her stillborn infant on her back, Bai Hokou, Dzanga Sangha Special Dense Forest Reserve, Central African Republic. December 20...

Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) female 'Mopambi' carrying her infant 'Sopo' aged 18 months on her back emerging from the forest into Bai Hokou, Dzanga Sangha Special Dense Forest Res...

Anup Shah / Western lowland gorilla (Gorilla gorilla gorilla) female 'Malui' carrying her stillborn infant on her back, Bai Hokou, Dzanga Sangha Special Dense Forest Reserve, Central African Republic. December 20...

David Pattyn / Great Crested grebe (Podiceps cristatus) swimming in early morning light carrying chick on back, La Dombes area, France, July