Simple explanation: both matings occurred, but Neanderthal communities went extinct. So since the child is reared in the community of the mother, we only get Neanderthal male admixture
That was my first assumption on reading the title, but the article mentions two other things:
The male-gene bias apparently persisted for subsequent generations after the initial human/Neanderthal pairing: male children of mixed ancestry had more offspring than their female siblings
In Neanderthal communities, the bias was reversed (i.e., more human DNA was retained in the X-chromosome female line.)
Simple explanation: both matings occurred, but Neanderthal communities went extinct. So since the child is reared in the community of the mother, we only get Neanderthal male admixture
That was my first assumption on reading the title, but the article mentions two other things:
The male-gene bias apparently persisted for subsequent generations after the initial human/Neanderthal pairing: male children of mixed ancestry had more offspring than their female siblings
In Neanderthal communities, the bias was reversed (i.e., more human DNA was retained in the X-chromosome female line.)