Complex sentence: In the 1970s, traditional views on the moral standing of animals were notably challenged by Richard D. Ryder and Peter Singer, who introduced the notion of speciesism, which they defined as discrimination on the basis of species for what they saw as morally irrelevant reasons.
Split into simpler sentences: In the 1970s, traditional views on the moral standing of animals were notably challenged by Richard D. Ryder and Peter Singer, who introduced the notion of speciesism. This is defined as discrimination on the basis of species for what might be considered morally irrelevant reasons.