Argument: Marriage can evolve, but only in context man and woman
Margaret A. Somerville. "The case against "Same-sex marriage." Marriage Institute. April 29, 2003: "One argument in favour of same-sex marriage is that the culture of marriage has changed over the years and that recognizing same-sex marriage is just another change. A common example given is the change in the status of the woman partner, in that marriage is now seen as a union of equals. But that change goes to a collateral feature of marriage, not its essential nature or essence as recognizing same-sex marriage would. In short, these two changes are not analogous; rather, they are fundamentally different in kind."
Susan Shell. "The liberal case against gay marriage." Public Interest. Summer, 2004: "An emphasis on what unites all Americans with regard to marriage might help stem the slide toward thinking that marriage can be anything we choose. It might help remind us that liberalism is not only about choice; it is also about acknowledging reasonable political and moral limits."
Jack Kerwick. "The failed case for gay marriage." Intellectual Conservative. February 19th, 2010: "Response to (3): [(3). It is true that the legalization of "same-sex marriage" would require a modification of "the traditional definition" of marriage, but the history of the understanding of marriage is nothing short of the history of the modifications that it has endured. The ideal of monogamous marriage, for example, with which contemporary critics of "same-sex marriage" unfailingly equate "traditional marriage," isn't "traditional" at all, as far as history is measured; rather, by this standard, it is a relatively recent development.] It is of course true that, historically, the concept of marriage admits of a multiplicity of conceptions. On this score I will say more below, but for now it should suffice to point out that while it is wildly unlikely that the understanding of any idea can escape modification, given the constant flux characteristic of our world, not all changes are of the same order or kind. Some changes are identity enhancing, while others extinguish the identity of the being to which they occur.
Thus, that the understanding of marriage has undergone alterations suggests that critics who (foolishly) speak as if this is the very first time any such changes have been proposed are driven by either ignorance or dishonesty, but it does not establish that the modifications that are now being recommended should be endorsed."
David Blankenhorn. "Protecting marriage to protect children." LA Times. September 19, 2008: "Marriage as a human institution is constantly evolving, and many of its features vary across groups and cultures. But there is one constant. In all societies, marriage shapes the rights and obligations of parenthood. Among us humans, the scholars report, marriage is not primarily a license to have sex. Nor is it primarily a license to receive benefits or social recognition. It is primarily a license to have children."