Human Neanderthal Hybrid Update

Apparently the documentary I saw was belated or a rerun. Did a little digging and found out that the bones were found in Portugal near the coast north of Lisbon. It was a skeleton of a four-year-old boy with features of modern human but limbs proportionately Neanderthal. Research from DNA tests found links of modern human with Cro-Magnon but no apparent link with Neanderthal. Don't know if it's possible that their DNA 'disappear' with interbreeding or they just evolved and 'became' modern human hence the lack of trace of DNA. Just my wild imagination.