We humans are a diverse species, both at the phenotypic and the genetic levels. The genetic diversity of current human populations has been shaped by various demographic and evolutionary as well as some cultural factors. Thus, studying how genetic variation is distributed through individuals around the world can provide insights into (i) when and where our human ancestors first appeared on the planet, (ii) the dynamics of admixture with other Homo species not existing anymore, (iii) migration waves that brought humans across the world and (iv) processes of adaptations towards environmental and other factors that shaped human genomes and phenotypic traits. Additionally, the quantification of genetic variation between human populations provides data evidence for elucidating whether humans can be classified according to genetically homogeneous groups or not, with implications for medical and forensic studies. Hence, studying human genetic diversity is important for better understanding of our past, presence and future.

Key concepts:

• Studying human genetic variation adds important insights for inferring human origins.
  
• Human genetic variation is highest in Africa, and non-Africans reflect a subset of diversity of Africans.
  
• Most genetic evidence supports a single common origin of modern humans in Africa and a recent spread out of Africa into different regions at different periods of time.
  
• Studying human genetic variation allows to some degree the reconstruction of human migration and adaptation history.
  
• Human genetic variation in Europe is gradually distributed with higher autosomal diversity in the south and lower ones in the north.
  
• European genetic variation implies that Europe was mainly settled from the south to the north and/or that the effective population size was larger in the south than in the north.
  
• Overall genetic variation between individuals is small and most of it is between individuals from the same population, whereas only a small proportion is expressed between continents.
  
• Some strong differences observed in particular loci between individuals from different, for example, continental regions have been driven by local positive selection.
  
• If applications of genetic variation, for example in medicine or forensics, include genomic regions with strong differences among continental groups, population substructure needs to be considered.
  
• It is as error prone to ignore the small proportion of genetic loci with strong differences between individuals from different geographic regions, including coded phenotypes, as it is to extrapolate from them to claim ‘racial’ differences between humans, which do not exist when considering the genome as a whole.