Large differences between LINE-1 amplification rates in the human and chimpanzee lineages.

The genomic evolution and causes of phenotypic variation among humans and great apes remain largely unknown, although the phylogenetic relationships among them have been extensively explored. Previous studies that focus on differences at the amino acid and nucleotide sequence levels have revealed a high degree of similarity between humans and chimpanzees, suggesting that other types of genomic change may have contributed to the relatively large phenotypic differences between them. For example, the activity of long interspersed element 1 (LINE-1) retrotransposons may impose significant changes on genomic structure and function and, consequently, on phenotype. Here we investigate the relative rates of LINE-1 amplification in the lineages leading to humans, bonobos (Pan paniscus), and chimpanzees (P. troglodytes). Our data indicate that LINE-1 insertions have accumulated at significantly greater rates in bonobos and chimpanzees than in humans, provide insights into the timing of major LINE-1 amplification events during great ape evolution, and identify a Pan-specific LINE-1 subfamily.