Do you believe that Moral Behavior is impossible without religion, or that higher animals like mankind evolve Moral Behavior over time?

First off, Marxism was never devised as a "Moral Code" at all, It was a theory of economics and historical direction and had little to do with morality. It's basic premise was that most of the benefits of industrial production should accrue to those who actually produced rather than all going to the owner class. It also proposed that this "historical direction" was part of the "natural order of human society" - it was wrong of course. But its corruption by the likes of Stalin and Mao is no more an indictment of Marxism than are the Crusades and the destruction of the native peoples of the "New World" by European Christians an indictment of the teachings of Jesus Christ.

Secondly, "man" has always "invent(ed) his own morality" and up until the last 2000 or 3000 years it had little relationship to any religion. Lao Tzu, a Chinese philosopher who lived more than 600 years before the birth of Christianity, devised a moral code for guiding man on the proper path that was premised on one simple, and rational, rule: "Do not do to others what you would not want done to yourself." This was not a code "handed down from on high," rather it was based on the belief of a shared experience and connection fundamental to all humans.

All of the great Greek moralists and philosophers - Plato, Aristotle, Socrates, et.al. - certainly did not draw their lessons from that of their gods. On the contrary, most Greek and Roman gods were capricious, selfish, morally bankrupt and often murderous entities (not unlike the Old Testament, Hebrew god, Yaweh, who had tendencies toward infanticide, massive cultural destruction, and in some cases, outright genocide).

History is replete with moral sensibilities remarkably similar across a broad range of human cultures dating all the way back to the time of the earliest homo sapiens - and there's even some archeological evidence of moral awareness in the time of the Neanderthals.

Btw, animals do not "behave rationally," as animals do not display an ability to reason. They are instinctual creatures (humans are also but their ability to reason allows them to transcend their hardwired instincts). They do sometimes display what we like to think of as "loyalty" but that's really a function derived from training not from reasoning.

Without the ability to reason there can be no rationality, nor morality, for that matter.