Andrew Parkinson / 2020VISION / An adult male Mallard (Anas platyrhynchos) comes in to land, backlit by evening sunlight, Derbyshire, England, UK, March. Did you know? In addition to the colour differences between male and female du...

Bruno D'Amicis / Visible differences between monospecific Spruce (Picea abies) forest affected by Bark Beetle (Curculionidae), and mixed forest (right), from a high perspective. West Tatras, Slovakia, September 2007.

Nick Garbutt / Female Silvered langur (Trachypithecus cristatus / Presbytis cristata) carrying very young infant (less than 2 weeks). Bako NP, Sarawak, Borneo, Malaysia

Luiz Claudio Marigo / Aerial view of the meeting of the brown waters of River Mamoré and the black waters of River Guaporé / Itenez during the great flood of 2008, at the border of Brazil (Rondônia State) and Bolivia (B...

Luiz Claudio Marigo / Aerial view of Madeira River, where it is formed by the meeting of the waters of Beni River (clearer water, left) and Mamoré River at the border of Brazil (Rondônia State) and Bolivia (Beni Departme...

Mark Moffett / Ant (Acanthomyrmex sp) pair showing differences in size and morphology, Tangkoko Nature Reserve, Indonesia

Barry Mansell / Treefrogs {Hyla crucifer} (light) + {Hyla crucifer bartramiana} (dark) Florida, USA

Paul D Stewart / Elephant skeleton engraving in Cuvier's 'Ossamens Fossiles' (1812). Cuvier, the master of comparative anatomy, referenced modern species with extinct fossils to reveal their affinities and differences...

Paul D Stewart / Illustration of bear skulls of living and extinct species, engraving in Cuvier's 'Ossamens Fossiles' (1812). Cuvier, the master of comparative anatomy, referenced modern species with extinct fossils t...

Petra Wegner / Eight Miniature Poodles, black, apricot-white, silver, black-and-tan, apricot and harlequin, sitting and lying

Petra Wegner / Rex Lop-eared Dwarf Rabbit, blue-white and apricot, Satin Dwarf Rabbit and Lion-maned Dwarf Rabbit

Petra Wegner / Miniature Poodles, black-and-tan, black-and-white, harlequin and apricot-white

George McCarthy / Adder with young showing size and markings difference {Vipera berus} Surrey UK