... by 'superior' modern human genes which spread after interbreeding between the two species more than 100,000 years ago

• German experts were able to analyse male Neanderthal DNA for the first time
• They found evidence of early interbreeding between Neanderthals and humans 
• Bad mutations had arisen in the Neanderthals' own Y chromosomes, they said
• Natural selection therefore favoured the modern human male chromosomes 
• As the Neanderthals bred with each other, human genes grew more common 
• The original Y chromosomes likely vanished within tens of thousands of years

Neanderthals' original Y chromosomes were gradually wiped out in the wake of interbreeding with modern humans more than 100,000 years ago, a study found.

Once injected into the Neanderthal gene pool, the 'superior' Y chromosomes from the humans spread throughout the ancient hominid population by natural selection.

This saw the Neanderthals' own Y chromosomes — which had acquired bad mutations as a result of their small population size — ultimately get totally replaced.

The process would have taken in the order of tens of thousands of years, German experts predicted based on models of the Neanderthals' shifting genetic makeup.

The findings support the results of previous studies, which found genetic transfer occurred from humans to Neanderthals prior to the major out-of-Africa migration. 

The presence or absence of a Y chromosome in mammals typically determines an individuals' sex — with the Y chromosome only passed down from father to son.