I don’t think the point is whether you can be moral without God, at least relatively moral anyway. The point is where do morals originate. The Bible says that the Law (10 commandments) was written on our hearts so we have no excuse. See Romans 2:14-15. Take God out of the equation and I suppose morals developed by (non existent) macroevolution or perhaps the Big Bang caused them and they floated around space waiting for a worthy host and man finally fit the bill?
Maybe early man realized through reasoning that is was best to treat others as they wanted to be treated for the betterment of everyone. Humans have reasoning power...we have put men on the moon while animals have not...