President Barack Obama recently announced his support for same-sex marriage. He utilized the biological concept of "evolution" as an analogy to describe is changing views. Evolution, of course, describes the changes that living organisms experience over generations as they move from simple to more complex physical structures through mutations and natural selection.
What about marriage and evolution as a biological concept instead of an analogy?
I do not see how biological evolution supports same-sex marriage.
Marriage between a man and a woman is a social convention that we can define anyway we want as a society, but it is based upon natural processes. Over the course of four million years, biological evolution has selected two genders for the reproduction and rearing of offspring to perpetuate the human species. Human reproductive organs possess an evolved compatibility. The male's external reproductive organs and the female's mostly internal reproductive organs when properly functioning enable intercourse and reproduction. Although instinct does not determine human behavior the same way that it does in other species, natural processes involving various visual, auditory, and olfactory cues influence human mating. Facial appearance, voice pitch, and the more subtle influences of pheromones such androstadienone and copulence draw the sexes together. Sexual desire itself as a visceral urge is expressed through human reproductive faculties. These biological phenomena assist in establishing human mating generally and finding genetically advantageous mates specifically. The union between a man and a woman with the potentiality for children is an essential property of the concept of marriage.
For some interesting research on this see here.
Men and women engage in sexual intercourse. They have children. They form kinship networks based upon consanguinity.
Same-sex couples do none of these things. Through some malfunction of nature, probably through hormonal deficiency during intrauterine development, about one percent of people inherit an orientation for the same sex. They pick up on the wrong visual, auditory, and olfactory cues. Some of these people appear to have some kind of gender identity disorder as well.
This presents a biological and social problem. Same-sex couple cannot engage in sexual intercourse, properly speaking. Same-sex couples cannot give birth to biological children. Same-sex couples cannot form kinship networks based upon consanguinity. Consequently, there seems to be no compelling reason to provide legal recognition to same-sex relationships.