Nature herself talks about the decrees of God
Dr. Roberto Miranda(Audio: Spanish)
The apostle Paul is saying that far from being a human right or an acceptable behavior by God, homosexuality is rather the consequence or the manifestation of God's wrath on a humanity or on a sector of human beings that has stubbornly resisted His Will and try to ignore what God says precisely about what behavior He wants men and women to follow in the sexual area and in the area of marriage.
So Paul tells us in Romans 1:18 onwards that there are people who have been determined to obscure and hinder what God has declared in nature itself. The first argument that we as Christians have to offer against homosexual behavior is that nature itself is clear regarding what God wants concerning the sexual behavior of human beings, indeed the animals themselves are clearly structured in terms of a male or a female and in the animal world animals behave in a heterosexual, non-homosexual manner.