It is difficult to prove that the Starchild (SC) IS alien, but there is already significant evidence that it is NOT entirely human. No expert, no scientist, and no doctor has ever been able to prove that the SC is 100% human. View images (whole exclusive DNA photographs) which present compelling evidence that the SC may very well prove to be a human-alien hybrid, with a human mother and an alien father.
But to summarise the findings: Carbon 14 dating reveals that the remains of the Starchild and the Adult Female are both 900 years old +/- 40 years. Bone chemistry scans indicates they lived in the same general area of high desert where their bodies were allegedly found. After death, their remains lay together in the same mine tunnel, corroborated by identical mineral encrustation on the surface of the bones. It would logically follow that both skulls would have experienced the same level of natural DNA degradation, and DNA should have been equally easy to extract from both. The Adult Female's maternal and paternal DNA was easily recovered, yet only the Starchild's maternal DNA was recoverable using the human-only primers that seek out human DNA. The incredible--but logical--conclusion is that the Starchild paternal DNA is simply not responsive to HUMAN primers, meaning that the Starchild's father is not entirely human.