All non-Africans inherit approximately 2% Neanderthal ancestry. Melanesians inherit additional 2-5% Denisovan ancestry. Initial Neanderthal admixture proportion reached 6-9% in ancient Eurasians. Neanderthal ancestry steadily declined due to purifying selection. Multiple independent admixture pulses explain varying archaic levels across populations. East Asians retain more Neanderthal DNA than Europeans. Neanderthal ancestry depleted on X chromosome indicating male Neanderthal-female human bias. Africans carry archaic ancestry from unidentified African hominins. Large genomic deserts lack archaic DNA due to selection against deleterious variants. Neanderthals accumulated weakly deleterious alleles from small population size. Surviving archaic alleles boost immunity via genes like OAS1 and TLR1. Neanderthal BNC2 allele influences European skin pigmentation. Denisovan EPAS1 enables Tibetan high-altitude adaptation. Archaic sequences disproportionately affect gene regulation and expression. Human gene flow into Neanderthals occurred 100-300 kya.