Background: Global analysis of 3 human genomes of increasing levels of evolution (Neanderthal /Sapiens Build34 / Sapiens hg38) reveals 2 levels of numerical constraints controlling, structuring and optimizing these genome's DNA sequences. A global constraint -called "HGO" for "Human Genome Optimum" -optimizes the genome at its global scale. The same operator applied to each of the 24 individual chromosomes reveals a hierarchical structure of these 24 chromosomes.