Can Morality come from Evolution Alone?

My Dear Atheist,

You wrote me to explain why you think it is no longer necessary to believe in God. I appreciate that. It was a friendly gesture. I hope you don't mind if I return my own thoughts - especially in response to what you wrote on morality and ethics. You say,
Altruism is an evolutionary response to the pressures of competition in the world – we can’t help but find it enjoyable
So, according to your theory, we act in a moral way because evolution has designed it that we get pleasure from doing so. Please let me briefly share four issues I have with your new theory. 

Animal Morals?First of all, when some of our 'evolutionary animal cousins' eat their own children or when a male forces sex on a female, is this morally wrong? Can animals act in an immoral way? You argue for a universal moral metric stick. But given the evolutionary process, how? Was there a definite moment in history when the organic motions we call cannibalism and rape became ‘wrong’? If it's ok for some animals (and they seem to enjoy it) when did it become wrong for us? 

Past Morals?Secondly, if altruism evolves, what does this mean for people who do not share our modern, Western moral standards? What about Ghengis Khan and crew? Did they act that way because they lived 900 years ago and evolution had not advanced their altruism enough yet? Are we morally superior because 900 years has biologically advanced us? What about ISIS? They do similar things to the Khans. Are they genetically inferior to you and me? If our species is to advance, should we get rid of these altruistic retards?
But then, if morality comes from our evolution, why berate immoral people? Why do you give, as you did in your letter, the ancient Israelis such a hard time? They were just doing what genetically gave them pleasure. You might as well call salmon to repent for not having legs.

Future MoralsThird, if altruism has developed to where it is now to help our species survive, we should expect it to change in the future. Right?

What if our hard wiring changes so that we see evil as what we now see as good – and vice versa? What if we start getting pleasure from other sorts of behaviours? Birth rates in the West are low. Perhaps our hardwiring will change in order to increase our offspring. It may have us do things to our women that we now consider unethical so that they will have more babies. What if ISIS and their sex slavery, instead of being backwards, is really the next step in the evolutionary process to replenish the species and make a stronger race?
If morality evolved, then that means morality changes. Your eternal standard - which you say evolution can provide - is a concept foreign to the material universe you live in. The current morals of homo sapiens are just a stopover on the road to something else. No use in getting too attached to them.

Fun ImmoralityLastly, why should I be moral? Because it gives me pleasure? Really? I'm sure I could find many things pleasurable that we would generally consider to be immoral. So could you. In a given situation, why should I obey the 'altruism impulse' which you say that evolution gave me, but not my impulse for sexual satisfaction or longing for power. Evolution gave me those impulses too. Why is it 'wrong' to follow the one but not the other?
I leave it with you to respond. 
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