A female rhino that has survived a brutal dehorning by poachers using a chainsaw four months earlier at the Tugela Private Game REserve, Colenso, Natal, South Africa, Nov. 9, 2010. (Brent Stirton/Reportage Betty Images/National Geographic Magazine)
A male polar bear climbs precariously on the face of a cliff above the ocean at Ostrova Oranskie in northern Novaya Zemlya, attempting to feed on seabird eggs. (Jenny E. Ross)
serotonin - happiness, satisfaction
dopamine - love, passion, pleasure
acetylcholine - learning, memory, dreaming







