"For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves" (Romans 2:14).
In Romans 2 Paul is proving that there is a right and wrong and that people know it.  The evidence is in the moral and legal behaviour of the human race.  Every time a person judges another, he is affirming that there is a right and a wrong.  "Therefore thou art inexcusable, O man, whosoever thou art that judgest: for wherein thou judgest another, thou condemnest thyself; for thou that judgest doest the same things" (Romans 2:1).
Evolutionists dictate that our characteristics are there because they offer an evolutionary advantage.  So they are stuck with the almost amusing contradiction of loudly proclaiming the survival of the fittest ("might is right") and then now adding the survival of the most moral. If it is an evolutionary advantage to kill and eat your enemy, how can it also be an evolutionary advantage to do unto him as he you would have him do unto you?
In Romans 2:14, Paul considered the nations that did not have the written law of God like the Jews did.  He observed a culture of laws that arose out of their moral behaviour and went on to give three logical conclusions in the next verse.
"Which shew the work of the law written in their hearts" (Vs. 15a).  Universal legal behaviour shows a legal principle working within.  Everybody has a sense of right and wrong inherent in their humanity.  "their conscience also bearing witness" (Vs. 15b).  When we violate that moral code, we have a judge within us that condemns us, our conscience.  "and their thoughts the mean while accusing or else excusing one another" (Vs. 15c).  We show this further by our thoughts about the behaviour of others.
Paul's lesson to us is clear.  With such a built-in system of judgment of right and wrong, and of punishment, we have a ready proof that we realize deeply there is such a thing as sin.  We should be ready to accept the way made by God to gain His forgiveness and to be freed from the dominion of that sin in our lives.  The message of Romans, and the whole Bible, is that this way is through the salvation provided by God's Son when He gave Himself as a sacrifice for our sin on the cross.