I'd say we're in a transition from less rational to more rational.
At the very least we have the capability of empathy so there has been some ratio to this whole morality thing for some time now.
Whatever the reasons for its evolution, it allows us to think of ourselfs as if in the shoes of another. We even anthropomorphize, which brings us into trouble when we project our moral delineators on unsuspecting systems.
And i think that this kind of reflection is realy the basis for any rational moral structure. Reflection being, in a way, a simulation where you analyze the situation from someones viewpoint.
But it somehow seems to me that there is no way to make morality perfecty rational. It will always require a viewpoint and choosing the viewpoint is a moral choice in itself. Is it good, per se, to decide what is good?
I hope for the sake of humanity that you are right that we are in a transition from irrational to rational.
There is a way to make ethics rational. Read about universally preferable behavior.
The point can be made pretty hard.
Ethics is based on impulses from our genes. This is by now a medical fact. In the basis these impulses are selfish in a very direct way. They re there to protect the individual. But humans evolved as social animals and so parts of these genes had to start coding for impulses that lead to behaviour that is beneficial to the local society.
Social progress has allowed us to see these impulses from a bigger viewpoint so we can apply them to ever bigger structures.
So now you no longer just fight for the rights of yourself or your family, you fight for the rights of all woman, for the rights of all humans and even for the rights of animals.
That much has more or less been achieved on a social level on basis of these vague impulses from our genes.
What science allows us to do is to find rationale in our projections outward into the bigger system.
We have found enough rationale to be sure that many animals are capable of experiencing pain in a similar way as humans do. So then it becomes science that allows us to extend our ethics to other systems in a meaningfull way.
So the more we know about the universe the more we can extend our notions of what is a good balance of cooperation.
But they are human notions neverteless so your mileage may vary.
Anyway, i don't believe in mumbo jumbo like universally preferrable behaviour.
Anything truely universal will not touch our human condition. We, together with our ethics, are amazingly specific. If we had no sufficently developed brains there would be no ethics to think about. You would be worried about how to get food and about not being eaten. Which is the de facto situation for most of life on earth.
For any ethics to be defined you first would need to set a goal. For us, it's survival of the species and anything we want to extend that to. Calling any of it universal would be the paramount of human arrogance. But what could you expect from a book written by a radio show host, right?