It also says that the relationship between male humans and female humans proceeds according to a design, or plan.
It also says, by the way, that deviating from the plan is abominable-but in this context, it's not the characterization of the deviation that is important, but the fact that is not part of the Creator's design.
As Darwin noted, natural selection is redundant to the notion of God being alive and well in the world. What most folks get wrong is that natural selection does not, per se, control the way man lives, though it is not entirely irrelevant. Man lives more often by unconscious selection or methodological selection. In the case of gays, the process of society relaxing it's restrictions against it is, obviously, a method by which the body of society diminishes in itself periodically of the gay influence. While the standard for most of the Roman Empire did eschew gay relationships, the upper crust did indulge, but with time, such behaviour is an end to itself. God is alive and well and active in the world, and yes, gays, while part of the plan, are not the essential part of the plan. The correct parallel is the tares and the wheat. Tares have a useful function, but they are not the bread of life as is the wheat. Sometimes they are left in the field for a time, but ultimately they are all separated from the wheat.