Thomas Marent / Gelada Baboon (Theropithecus gelada) male and females huddling for warmth, Simien Mountains National Park, Ethiopia
00547926
Alan Murphy / Northern Bobwhite (Colinus virginianus) female and male, Texas
00547902
Alan Murphy / Eastern Bluebird (Sialia sialis) male and female, Texas
00547538
Alan Murphy / Eastern Bluebird (Sialia sialis) male and female, Texas
00543764
Anup Shah / Cheetah (Acinonyx jubatus) chasing Impala (Aepyceros melampus) female, Masai Mara, Kenya
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Donald M. Jones / Bighorn Sheep (Ovis canadensis) ram and ewe during rut, Montana
00521544
Donald M. Jones / Bighorn Sheep (Ovis canadensis) ram and female, western Montana
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Vincent Grafhorst / African Lion (Panthera leo) pair mating, Khutse Game Reserve, Botswana
00449261
Vincent Grafhorst / African Lion (Panthera leo) male and female courting, Khutse Game Reserve, Botswana
00423279
Michael & Patricia Fogden / Black-faced Impala (Aepyceros melampus petersi) male, females, and young drinking at waterhole, Etosha National Park, Namibia
00298031
Piotr Naskrecki / Bearded Weevil (Rhinostomus barbirostris) species displays interesting sexual polymorphism, Costa Rica
00216500
Pete Oxford / Chachi Tree Frog (Hyla picturata) pair, Cotacachi-Cayapas Reserve, northwest Ecuador
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Pete Oxford / Chachi Tree Frog (Hyla picturata) pair, Cotacachi-cayapas Reserve, northwest Ecuador
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Pete Oxford / Chachi Tree Frog (Hyla picturata) pair, Cotacachi-Cayapas Reserve, northwest Ecuador
00197159
Konrad Wothe / Fiddler Crab (Uca maracoani) waving, Caroni Swamps, Trinidad, West Indies
00141722
Tui De Roy / Great Frigatebird (Fregata minor) courting males vying for female's attention, Genovesa Tower Island, Galapagos Islands, Ecuador
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Tui De Roy / Great Frigatebird (Fregata minor) recently formed pair, female inspecting male in courtship display with extended gular pouch, Genovesa Tower Island, Galapagos Islands, Ecuador
00135659
Norbert Wu / Old-world Chameleons, male and female preparing to mate, Africa
00123856
Mitsuaki Iwago / Australian Sea Lion (Neophoca cinerea) male approaching a female to mate, Australia
00123748
Shin Yoshino / African Lion (Panthera leo) male and female, Masai Mara National Reserve, Kenya
00115838
Mitsuaki Iwago / Ostrich (Struthio camelus) male and two females running, Serengeti National Park, Tanzania
00113768
Mitsuaki Iwago / African Lion (Panthera leo) couple fighting during mating, Serengeti National Park, Tanzania
00109045
Mark Moffett / Strawberry Poison Dart Frog (Oophaga pumilio) group showing color variation from different islands, Bocas del Toro, Panama
01653960
Doug Gimesy / White-cheeked gibbon (Nomascus leucogenys) female and two offspring, a male and female, sitting in tree. White-cheeked gibbons are sexually dimorphic with females having golden fur. Babies are born go...
01551869
Bernard Castelein / Dimorphic egret (Egretta dimorpha) in white phase, flying, Ankarafantsika National Park, Madagascar
01546896
Carol Walker / Group of young Merens mares running with a dog in pasture, Northen France, Europe. February.
01546288
Paul D Stewart / Illustration of Cowslips (Primula veris) from 'Darwinism' by Alfred Wallace 1889. In 1862 Darwin reported how Primula plants have two forms of flowers, pin and thrum eyed, differing in the height and...
01546249
Paul D Stewart / Portraits of Cowslip (Primula veris) flowers, pin and thrum eyed, showing heterostyly ie stigma at different positions. This was noted by Darwin and shows a mechanism to avoid self fertilisation.
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Willem Kolvoort / Dimorphic Egret (Egretta dimorpha) on edge of Aldabra lagoon with coral 'mushrooms', Natural World Heritage Site, Aldabra 2006
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Willem Kolvoort / Dimorphic Egret (Egretta dimorpha) on edge of Aldabra lagoon with coral 'mushrooms', Natural World Heritage Site, Aldabra 2006
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Willem Kolvoort / Dimorphic Egret (Egretta dimorpha) and Crab plovers (Dromas ardeola) on edge of Aldabra lagoon with coral 'mushrooms', Natural World Heritage Site, Aldabra 2006
01536556
Willem Kolvoort / Dimorphic Egret (Egretta dimorpha) and Crab plovers (Dromas ardeola) on edge of Aldabra lagoon with coral 'mushrooms', Natural World Heritage Site, Aldabra 2006