WHY DO BIOLOGISTS ARGUE LIKE THEY DO

''Theoretical pluralism'' obtains when there are good evidential reaso ns for accommodating multiple theories of the same domain. Issues of ' 'relative significance'' often arise in connection with the investigat ion of such domains. In this paper, I describe and give examples of th eoretical pluralism and relative significance issues. Then I explain w hy theoretical pluralism so often obtains in biology-and why issues of relative significance arise-in terms of evolutionary contingencies an d the paucity or lack of laws of biology. Finally, I turn from explana tion to justification, and raise questions about the purpose and value of concerns and disagreements about relative significance.