Neanderthal inheritance

At http://phys.org/print381383366.html … Palaeolithic humans and genetics. At the end of the piece we are told there was admixture with Neanderthals around 45,000 years ago. The prehistoric human population had around 3 to 6 per cent of Neanderthal DNA. Today, this has declined as Neanderthal DNA is slightly toxic to modern humans (or some of us it seems). Natural selection is removing Neanderthal ancestry – which makes you wonder why it has taken so long to diminish to 2 per cent. Is it possible Neanderthal or Homo erectus DNA was once much more plentiful in prehistoric humans. Only a small sample of genetic material is available.