moral evolution

Skimming the comment section of a post a few days ago, I ran across a dispute about whether modern reactions to a problem would differ from those of the 15'th century. The riposte was "500 years of moral evolution." Hmm. I assume he meant "improvement across the board," though evolution can make things significantly worse from a general point of view--for example the blind snakes found in caves. It doesn't hurt them to be blind in the dark, but we'd say it's better to be able to see.

Some things are better--going by Christian standards. Torture and slavery are deprecated and illegal most places. But has there really been evolution to something better, or merely change to a different set of values? I know some people who care about immigrants, and are eager to open our borders as much as we can, whose belief is based strongly in their Christian faith and who care deeply about their families. On the other hand, I know some whose love and sense of duty for family is rather more attenuated than their ancestors'. They care for the stranger as much as for their families, which is in their case is mostly abstractly.

Why are we so certain our popular sexual mores are superior to our ancestors', and our neighbors'? I've never seen that proven, just asserted that autonomy is more important.