RESEARCH HIGHLIGHTS LINKS FOR WEB HUMAN EVOLUTION genes have evolved rapidly at the within these genes, including those International HapMap level of coding sequence in humans, such as olfaction and reproduction Project: http://www. hapmap.org and ties in with how gene-expression that have previously been highlighted Following changes might have evolved, with as targets of selection. However, a transcription-factor modifications number of new categories also stood the affecting the regulation of their target out, including genes that are involved genes. in metabolism. Intriguingly, this In a second study, Voight and might correspond to changes in the signposts of colleagues used a different strategy human diet during the expansion to identify regions containing alleles of agriculture, which fits in with the selection that have been under very recent authors’ estimates of the timing of selection and have not yet reached the selection that is captured in their Despite our fascination with the evo- fixation in the human genome. They study. lutionary processes that have led to took advantage of SNP data from the Much remains to be learned from the unique characteristics of humans, International HapMap Project for the approaches that were used in insights into the genetic basis of three different populations to locate both of these studies: for example, these changes have been limited. genomic regions that contain unusual the expression-based method has so Only a handful of genes have been patterns of linkage disequilibrium far been used only for genes that are pinpointed as strong candidates for that are indicative of an ongoing expressed in the liver, and the authors having undergone adaptive changes selective sweep — a process that of the second study stress that much in the human lineage, and our knowl- alters linkage disequilibrium patterns uncertainty remains about the actual edge of the underlying mechanisms and ultimately drives down genomic genetic targets of selection and the is also sparse. However, as illustrated diversity in the region surrounding a nature of the adaptation. Clearly, by two recent papers that use differ- positively selected allele. This analysis exploring the genetic basis of human ent strategies to identify regions and revealed many such regions through- evolution is a challenge that has only genes that have experienced selection out the genome, some of which just begun. during human evolution, the tools contain genes that have been shown Louisa Flintoft are now becoming available to make to have undergone positive selection ORIGINAL RESEARCH PAPERS Gilad, Y. et al. greater progress in this area. in previous studies. Expression profiling in primates reveals a rapid One theory is that changes in gene The authors also picked out the evolution of human transcription factors. Nature regulation have been key to human genes within their regions of interest 9 March 2006 (doi:10.1038/nature04559) | Voight, B. F. et al. A map of recent positive evolution, a hypothesis that can be that are the best candidates for hav- selection in the human genome. PLoS Biol. 4, e72 tested by examining gene-expression ing experienced selection. Several (2006) differences between humans and functional categories were enriched other primates. Gilad and colleagues used a multi-species microarray to assess differences in expression in the liver between over 1,000 human genes and their orthologues from three other primates. They identified 19 genes that are expressed at the same levels in the three non-human primates, but at higher or lower levels in humans compared with these other species. This is strong evidence that changes in the expression of these genes have been selected for specifically in the human lineage. Notably, the genes that show increased expression in humans were particularly enriched for transcrip- tion-factor genes. This is consistent with previous findings that such NATURE REVIEWS | GENETICS VOLUME 7 | MONTH 2006 | 1 © 2006 Nature Publishing Group .