What is natural is that which perpetuates the existence of the organism in question.
For a man having sex with a women means the genes he carries have a higher likely hood of success.
Not all ways of survival are direct. For example a man who cannot have children may still increase the popularity of his own genes by helping with his relatives children or simply helping society at large.
From this "selfish gene" perspective with a focus on natural selection. I don't think homosexual interactions cause any increase in the likelihood of gene survival. Though I may be wrong on this.
I don't recommend sodomy for anyone. I would never do that to a woman or a man.
Reason is the anus is an area of high concentration of ecoli. Anal insertion can cause small cuts in this area. Thus ecoli can go into these cuts and cause infection.
Though there may be a cultural and evolutionary reason that humans will attempt to push depopulation.
The argument that humans need depopulation now and homosexuality is an effective means of that, is one thing I'm definitely considering.
Overall I discourage sodomy for both men and women. But at the end of the day everyone has the right to do anything I'd it doesn't effect others negatively.
RE: 3 Golden Nuggets a day - on Cultural Bias and Feminism