I am intrigued by this claim. Why do you say so?
Morality is essentially another way of saying "right or wrong." What is right or wrong is NOT instinctual, they're ingrained societal imperatives.
For example, A person everyone today would call a sociopath, when put back in say... ancient Greece would be known as one of their greatest leaders, or an epic hero.
Another example from ancient Greece. Back then it was normal and expected for men to strip naked, coat themselves in olive oil, and wrestle in the nude. I'm sure most (american at least) men's involuntary shudder at that mental image will tell you everything you need to know about its "morality" today. (note: I have no problem with gay men)
When broken down to it's most basic structure (it's, naturally, far more complex in reality), enough of a population feels a certain act is "wrong," so they form rules/laws against that act. Eventually the belief that act is wrong becomes a part of the society as a whole, and it starts to be "morally reprehensible" to do that act. The tie-in is, that those beliefs that an act is right or wrong are based on emotional reaction.
A killing is morally wrong because we take a look at the effects and are horrified, even if we're the one who did it.
For the majority of human history, a killing was just that, the end of a life. In many cases it was a
good thing, proof of your manhood or some such. Therefore, it
wasn't morally wrong. It could even be morally right.
The same works for positive morals, as seen by the actions of people portrayed as heroes by the population. Look at Odysseus from the Iliad and Odyssey, and compare his actions to Superman, or Batman, or any of the modern day "heroes." You'll find more in common with the villains than the heroes in that example.
All that's not even getting into the various moral states sex has been under over the millennia.
At any rate, I'm 1/2 asleep while typing this, so might not be the best explanation, but should get the basics of what I mean across.