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These groundbreaking laws foreshadowed and influenced the shifting attitudes toward nonhuman animals in their rights to humane treatment which Richard D. Ryder and Peter Singer would later popularize in the 1970 s and 1980 s .
 Richard D. Ryder, Peter Singer
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Richard D. Ryder, Peter Singer