Science News, a long time ago, reported finding on "homosexual " frogs. They found that some male frogs of a certain species became homosexual when there were too many males and not enough females. They found that the frogs brains changed in a specific area and that when the ratio came back to normal, the frogs did also both in behavior and brain.
They were not sure if the behavior caused the brain change or the brain change brought on the behavior.
So, at least for one species of frog, it is "natural", but only when there are too many males. But the finding also says that it is reversible.
It would be interesting to see if those frogs that changed were less aggressive than others that did not, and took the easy way out.
China is going to be having a similar problem due to its one child policy and parental penchant for boys. Girls have either been aborted, killed at birth, or abandoned and adopted out of the country. In a few years it's going to become evident that there are far more men than women and that not every man will be able to find a wife because there aren't enough to go around. Then the sociologists can start looking at what is happening.