Unnatural Selection

 is a gameplay achievement and trophy in Red Dead Redemption

Description
"Kill one of every animal species in the game in any game mode."

Tips

 * Animal kills do not cross over from Single Player to Multiplayer. You must kill the full list of animals in one or the other, and not a combination, in order to acquire this achievement/trophy.
 * It is not necessary to skin the animals. Track what kind of animals killed in "stats->misc", just compare this list with the animals in the stats.
 * Animals you haven't killed won't be listed at all. There are no "zeros" displayed.
 * There are animals that do not count towards this achievement: Cows, goats, and pigs.

List of Species
To unlock this achievement/trophy, the player must kill each of the following animals at least once:
 * 1) Armadillo - The Frontier and in Mexico.
 * 2) Bear - The Tall Trees area in the North.
 * 3) Beaver - These are in the Tall Trees area in the North.
 * 4) Bighorn - The mountains in the Frontier and Mexico, and in the Tall Trees area in the North.
 * 5) Boar - Pike's Basin, the Tall Trees area, just North of MacFarlane's Ranch or in the marsh near Thieves' Landing.
 * 6) Bobcat - Mexico and the Tall Trees area.
 * 7) Buffalo - Buffalo can be found in the Great Plains, most commonly to the Northwest of Blackwater.
 * 8) Cougar - In the mountains and hills on the Frontier and Mexico.
 * 9) Coyote - On the Frontier and Mexico, listen for their whiny howls.
 * 10) Crow - All three areas, listen for their caws.
 * 11) Deer - All three areas.
 * 12) Eagle - Tall Trees and Nekoti Rock areas of the North.
 * 13) Elk - Tall Trees area.
 * 14) Fox - Near Riley's Charge on the Frontier and in the Tall Trees area in the North.
 * 15) Hawk - The Frontier and Mexico.
 * 16) Horse - Wild
 * 17) Horse - Domesticated
 * 18) Owl - All three areas, only at night.
 * 19) Rabbit - All three areas.
 * 20) Raccoon - All three areas.
 * 21) Seagull - At the docks in Blackwater.
 * 22) Skunk - Around MacFarlane's Ranch on the Frontier.
 * 23) Snake - All three maps, listen for snake hissing or rattling while you are riding then check around on the ground.
 * 24) Songbird - Near the towns on all three maps.
 * 25) Vulture - All three areas, usually near death, e.g., completed gang hideouts, signs of trouble in missions.
 * 26) Wolf - All three areas, but in abundance in Mexico and the Tall Trees area.

Trivia

 * The name of the achievement is a parody of Darwin's theory of natural selection. Players must seek out and eliminate animals, intervening in the natural process.
 * While shooting an animal Marston will occasionally shout "I love natural selection!" or "Blame Darwin!"
 * The picture seems to be a meat cleaver and a pair of small meat hooks used when butchering. This is because it is resembling a butchering of the animals, which means a unnatural killing of something or doing it in a horrific way.