Why do biologists argue like they do?

Theoretical pluralism obtains when there are good evidential reasons for accommodating multiple theories of the same domain. Issues of "relative significance" often arise in connection with the investigation of such domains. In this paper, I describe and give examples of theoretical pluralism and relative significance issues. Then I explain why theoretical pluralism so often obtains in biology-and why issues of relative significance arise-in terms of evolutionary contingencies and the paucity or lack of laws of biology. Finally, I turn from explanation to justification, and raise questions about the purpose and value of concerns and disagreements about relative significance.