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In his book " Systematics and the Origin of Species " ( 1942 ) he wrote that a species is not just a group of morphologically similar individuals , but a group that can breed only among themselves , excluding all others .
 Systematics and the Origin of Species
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 Systematics and the Origin of Species