Passage Summary: An ethicist argues that because whooping cranes are rare, saving one is more important for the species than saving a common sandhill crane, so we should prioritize the rare ones.

Conclusion: We have a stronger moral obligation to protect an individual whooping crane than an individual sandhill crane.

Reasoning: Whooping cranes are endangered, making each individual more vital to the species' survival than a member of a non-endangered species like the sandhill crane.

Analysis: The argument moves from a biological fact regarding rarity to a moral conclusion about our duty to protect. The underlying principle must bridge this gap by linking the importance of an individual to its species' survival with the level of moral obligation we have toward that individual. We are looking for a rule that states the more critical an organism is to its species' existence, the greater our duty to preserve it.