Final answer:
Altruism is the ethical trait that was essential for human survival, involving long-term parental care and other behaviors that improve offspring survival.
Step-by-step explanation:
Because human offspring take over 15 years to attain adulthood, it was essential humans developed altruism to ensure the survival of their offspring. Altruism refers to behaviors that reduce one's own fitness while increasing the fitness of another individual. In humans, this could involve a variety of behaviors such as long-term parental care, sharing resources, and teaching offspring survival skills. Evolutionary ethics suggest that altruistic behavior may have been advantageous for early human societies, ensuring not only the survival of their offsprings but also the continuation of their genetic lineage. This ethical trait was likely a result of both natural selection favoring those who engage in altruistic acts and the cultural transmission of these behaviors to successive generations.