Is a father's failure to serve mother with a paternity action faulty?

Father claims the court's criticism of his failure to serve mother with the paternity action was faulty because it was speculative whether mother would have responded and, in any event, the court could not establish paternity without a DNA test so serving mother would have been a futile act. He further speculates that it would have been fruitless to contact the maternal grandmother to obtain information given her hostility toward him and her complicity in mother's attempts to prevent him from parenting the minor. In assessing whether a juvenile court erred and whether that error was harmless, we do not engage in speculation. Any determination of error must be made on the basis of the evidence before us. (Coy v. Iowa (1988) 487 U.S. 1012, 1021-1022 [101 L.Ed.2d 857, 867]; see People v. Bolin (1998) 18 Cal.4th 297, 334; In re J.N. (2006) 138 Cal.App.4th 450, 461.)