with animals like fish and lizards is that their brains dont really make choices in the same way. they much more genetically driven in their choices compared to mammals and great apes. what the examples of animals being homosexual shows that even when driven by mostly genetic impulses homosexuality occurs. which means it's more like being born black, asian, or blue eyed (minus the fact that those examples are inherited while homosexuality, currently has no proof of inheritance).
not to say that gay marriage shouldn't be allowed even if it WERE a choice. proving that it's natural is simply a destruction of one of the religious group's main arguments, that being the one where they say it's unnatural therefore it's "wrong."
OK, I hear your second argument although the religious argument "it's unnatural therefore it's wrong" is pretty weird.
If the unnatural attribute is a rational reason for banning something, religions has to be banned foremost. Never heard about a lizard church...
