cis-regulatory elements changes affect the transcription start sites (TSS) of genes. 471 DNA sequences are found to be enriched or depleted in regards to histone trimethylation at the H3K4 histone in chimpanzee, human, and macaque prefrontal cortexes. Among these sequences, 33 are selectively methylated in neuronal chromatin from children and adults, but not from non-neuronal chromatin. One locus that was selectively methylated was DPP10, a regulatory sequence that showed evidence of hominid adaptation, such as higher nucleotide substitution rates and certain regulatory sequences that were missing in other primates. Epigenetic regulation of TSS chromatin has been identified as an important development in the evolution of gene expression networks in the human brain. These networks are thought to play a role in cognitive processes and neurological disorders. An analysis of methylation profiles of humans and primate sperm cells reveals epigenetic regulation plays an important role here as well. Since mammalian cells undergo reprogramming of DNA methylation patterns during germ cell development, the methylomes of human and chimp sperm can be compared to methylation in embryonic stem cells (ESCs). There were many hypomethylated regions in both sperms cells and ESCs that showed structural differences. Also, many of the promoters in human and chimp sperm cells had different amounts of methylation. In essence, DNA methylation patterns differ between germ cells and somatic cells as well as between human and chimpanzee sperm cells. Meaning, differences in promoter methylation could possibly account for the phenotypic differences between humans and primates. Research has also shown surprisingly amounts of conserved tissue-specific methylation, in line with phylogenetic relatedness Chickens Red Junglefowl, an ancestor of domestic chickens, show that gene expression and methylation profiles in the thalamus and hypothalamus differed significantly from that of a domesticated egg-laying breed. Methylation differences and gene expression were maintained in the offspring, depicting that epigenetic variation is inherited. Some of the inherited methylation differences were specific to certain tissues, and the differential methylation at specific loci was not altered much after intercrossing between Red Junglefowl and domesticated laying hens for eight generations. The results hint that domestication has led to epigenetic changes, as domesticated chickens maintained a higher level of methylation for more than 70% of the genes. Role in evolution The role of epigenetics in evolution is clearly linked to the selective pressures that regulate that process. As organisms leave offspring that are best suited to their environment, environmental stresses change DNA