Christians: do you claim to have an ‘ultimate moral foundation’?

Or do you accept that human society has been progressively getting more and more complex over the last few thousand years and our sense of right and wrong too has been progressively getting more and more complex? So there is no ‘ultimate moral foundation;’ our morals have been evolving along with our society and we made the morals, not some imaginary god, right? We recognized that murder and stealing were wrong so we outlawed them, right? This is a much more rational explanation for morals than “God gave us morals and atheists have no morals because they don’t believe in God,” right?