What is “nature”?

Rom 1: 26-27
(KJV)
For this cause, God gave them up unto vile affections: for even their women did change the natural use into that which is against nature:
And likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is unseemly, and receiving in themselves that recompense of their error which is meet.
(NIV)
Because if this, God gave them over to shameful lusts. Even their women exchanged natural relations for unnatural ones. In the same way the men also abandoned natural relations with women and were inflamed with lust for one another. M en committed indecent acts with other men, and received in them selves the due penalty for their perversion.

This is one of the passages that some Christians use against gay people to say that they are “going against nature.” But you have to look at what the word “nature” means here. If you look at another passage, this same word is used in reference to hair length.

1 Cor 11: 13-15
(KJV)
Judge in yourselves: is it comely that a woman pray unto God uncovered?
Doth not even nature itself teach you, that, if a man have long hair, it is a shame unto him?
But if a woman have long hair, it is a glory to her: for her hair is given her for a covering.
(NIV)
Judge for yourselves: is it proper for a woman to pray to God with her head uncovered? Does not the very nature of things teach you that if a man has long hair, it is a disgrace to him, but that if a woman has long hair, it is her glory? For long hair is given to her as a covering.

In this passage, if you take “nature” to mean “the immutable biology of the natural world,” then you would have to assume that if you didn’t touch a man’s or a woman’s hair, the man’s hair would not grow long, but the woman’s would. But that’s not true. We know that if you don’t cut anyone’s hair, it’s going to grow just as long, whether they are a man or a woman. So obviously, “nature” here means something else. Cruden’s Complete Concordance says that this word can mean, among other things, “natural endowment or instinct” or “the existing system of things in the world.” Although the first definition might be something immutable, the second could definitely be something mutable, changeable. I think the key lies in 1 Cor 11: 16.
(KJV)
But if any man seem to be contentious, we have no such custom, neither the churches of God.
(NIV)
If anyone wants to be contentious about this, we have no other practice—nor do the churches of God.

Here Paul equates “nature” with “custom.” So it seems what he’s talking about is the long-held customs of the time, culture. Culture, customs, traditions are things that change. In all these passages, the words “nature” and “natural” all come from the same Greek root word. So if Paul is talking about customs regarding hair, is he talking about customs in the passage from Romans? Has “nature” changed? And how does this change how this passage is used?

With questions come more questions. What do you think?