Homosexuality is a natural state; it exists in nature and has done at the same level since before data about it started being collected.
If your concern is the continuation of the species then monogamy makes no sense.
Ancient tribes had transgender people, transgender people are not new, they just don't have to hide to the same extent for fear of violence from bigots like you and your ilk.
Homosexuality, polyamory and trans people are not new, it only seems so to you because the information available on the internet has burst your bubble of ignorance.
I recommend doing some research instead of just repeating what your prejudiced social group has told you.