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...

Doug Gimesy / Researcher placing a piece of platypus tissue (Ornithorhynchus anatinus) into a vial. From this piece, the DNA will be analysed back in the lab to help compare differences that may exist between popu...

Nigel Cattlin / Aerial view of Cereal crop variety trials plots to test differences between varieties such as yield and disease resistance.

David Perpinan / Sexual differences between female (left) and male (right) adult Egyptian tortoises (Testudo kleinmanni). dorsal view. Captive animals. small repro only

Rolf Nussbaumer / Sword-billed Hummingbird (Ensifera ensifera) male feeding from passionflower (Passiflora mixta), Papallacta, Ecuador, Andes, South America. January.

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...