It may very well be that pleasure in sex helps ensure procreation (LOL - look at the number of unplanned procreation that happens as a result of pleasure!), it may well be that animals do or not indulge in sexual behaviour with the same sex or solely for pleasure.
But what does any of it prove?
Our own human boundaries of what we can achive in support of nature, despite nature or against nature are so broad to have removed any link between 'natural' and 'right or wrong'.
Homosexuality just IS. There is growing resarch that it is innate, many many homosexual people will attest to having been aware of their sexuality a v early age. It just IS, it exists, and the only possible basis fo deciding whether something that exists is 'good ' or 'bad' is 'does it harm anyone?'.
No-one who doesn't want to take part has to. Gay relationships are as consensual as straight. No one is harmed, it does no damage to bystanders.
And for people who will tell their children not to persecute gay people even though you consider it wrong or sinful or unnatural - please, please as parents, think how devastating it would be to feel you are, to the core of your being, something that the person who you look to for unconditional love considers 'unnatural'.
I can tell you that many many young people who are alone and frightened on the streets of London have left home because they are afraid of coming out to their parents - parenst just like you, with your own justification - or have been thrown out bcause they are gay.
So, so sad. Is THAT really worth telling children that a loving relationship between two people following their innate inclination is not 'natural' or 'normal'?
Homophobia is so lacking in human empathy or compassion.