Ancient DNA sequencing technology has recently become a powerful tool for researchers attempting to uncover the
reasons why modern humans have survived while our closest species relatives, the Neanderthals, went extinct. This review
summarizes current studies of the Neanderthal genome and how these data inform our understanding of Neanderthal population structure and the evolutionary relationship between Neanderthals and modern humans. Additionally, the implications of evidence of interbreeding between Neanderthals and modern humans are examined in terms of the fitness consequences and inferred functions of Neanderthal introgressed DNA in living humans, and the challenges associated with determining whether or not a variant is adaptive are also discussed. The Neanderthal genome has thus far proven incredibly informative for understanding Neanderthal populations and their relationships with modern humans,
but additional work is necessary to link genetic differences between modern humans and Neanderthals to phenotypic differences that may have afforded modern humans a fitness advantage over the Neanderthals.