What is the molecular evidence that humans once interbred with Netherlands? With other how - extinct species?

"The proportion of Neanderthal-inherited genetic material is about 1 to 4 percent [later refined to 1.5 to 2.1 percent]. It is suggested that 20 percent of Neanderthal DNA survived in modern humans, notably expressed in the skin, hair and diseases of modern people. Extinction of a particular animal or plant species occurs when there are no more individuals of that species alive anywhere in the world - the species has died out. This is a natural part of evolution. But sometimes extinctions happen at a much faster rate than usual.