Christophe Courteau / Mountain gorilla (Gorilla beringei beringei) blackback, juvenile male demonstrating power. Volcanoes National Park, Rwanda.

Eric Baccega / Young woman from the Bodi tribe displaying elaborate scarification on the skin of her back, Omo Valley, Ethiopia, March 2015.

Eric Baccega / Young man from the Bodi Tribe having new scars made on his chest with razor blade, to make decorative skin scarifications. Omo Valley, Ethiopia, March 2015.

Sven Zacek / Black grouse (Tetrao tetrix) male displaying at lek on frosty morning, rear view. Vorumaa, Southern Estonia.

Nick Upton / Siberian flying squirrel (Pteromys volans) entering nest hole in Downy birch (Betula pubescens) tree trunk. Mature mixed forest, near Lisaku, Ida Virumaa, Estonia. April.

David Fleetham / Sea urchin crab (Echinoecus pentagonus), female inside Common banded urchin (Echinothrix calamaris) rectum. Hawaii.

Nayan Khanolkar / Bengal tiger (Panthera tigris tigris), female scent marking tree. Camera trap image. Pench National Park, Madhya Pradesh, India. January 2018.

Graham Eaton / Crenulation cleavage developed in Pre-Cambrian age, metamorphic, Chlorite Schist. Llyn, Wales, UK, May

Graham Eaton / Crenulation cleavage developed in Pre-Cambrian age chlorite schist, a metamorphic rock Llyn, Wales, UK, May

Jabruson / Ouled Rachid tribeswoman with baby strapped to her back, Kashkasha village near Zakouma National Park, Chad, 2010.

Sue Daly / Wild rose (Rosa canina) hip, Sark, British Channel Islands, Sept 2013

Enrique Lopez-Tapia / Back of girl at carnival, Eticoga, Orango Island, Bijagos UNESCO Biosphere Reserve, Guinea Bissau, February 2015.