I think he had a Sperm Donor that he knew, because he wanted a smart, trust worthy person that he could believe would not take his kids away in the future. I'm sure he also wanted to know what his kids would look like. MJ wanted to make sure they were not in his Race or likeness at all, his Dad made sure he believed he was ugly, so why would he want to have his own kids. Poor guy can't get any peace in death now either.