The recent availability of genome-scale genotyping data has led to the identification of regions of the human genome that seem to have been targeted by selection. These findings have increased our understanding of the evolutionary forces that affect the human genome, have augmented our knowledge of gene function and promise to increase our understanding of the genetic basis of disease. However, inferences of selection are challenged by several confounding factors, especially the complex demographic history of human populations, and concordance between studies is variable. Although such studies will always be associated with some uncertainty, steps can be taken to minimize the effects of confounding factors and improve our interpretation of their findings.The past few years have seen an explosion of studies using molecular data to detect Darwinian natural selection [1][2][3][4][5][6] . With the recent availability of large-scale genotyping data, genome-wide scans for genes or genomic regions that have been targeted by selection have become feasible. These studies have greatly advanced our understanding of human evolution and molecular evolution in general, but they have also sparked considerable controversy.The interest in detecting selection is twofold. First, it stems from a natural curiosity about our evolutionary past and the basic mechanisms that govern molecular evolution. Much of the work in this field through the past four decades has focused on quantifying the relative importance of Darwinian selection and random genetic drift in determining levels of variability within species, as well as divergence between species (for example, REFS 7,8 ). However, as evidence accumulates for a strong role of selection, efforts are increasingly concentrating on identifying and characterizing particular instances of selection and adaptation at the molecular level. In humans, in particular, there has been a strong interest in identifying genes that have undergone recent selection relating to key human traits such as cognitive abilities 4,9,10 .Correspondence to R.N., rasmus@binf.ku.dk. DATABASES Entrez Gene: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=gene
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NIH-PA Author ManuscriptA second motivation for studying selection stems from the realization that inferences about selection can provide important functional information. For example, genes that are targeted by selection acting on segregating mutations are more likely to be associated with disease (for example, REF. 3 ). Even small fitness effects can, on an evolutionary timescale, leave a distinct pattern. Therefore, it might be possible to identify putative genetic disease factors by identifying regions of the human genome that currently are under selection 3,11 . In general, positions in the genome that are under selection must be of functional importance, otherwise selection could not be operating.The aim of this Review is to discuss some of the major findings regarding selection in humans, and explain...