 To help clarify species and subspecies boundaries , and to establish whether morphology @-@ based classifications were consistent with evolutionary relationships , the phylogenetic relationships within the genus Nycticebus were investigated by Chen and colleagues using DNA sequences derived from the mitochondrial markers D @-@ loop and cytochrome b . Previous molecular analyses using karyotypes , restriction enzymes , and DNA sequences were focused on understanding the relationships between a few species , not the phylogeny of the entire genus . The analyses published in 2006 by Chen and colleagues ' proved inconclusive , although one test suggested that N. coucang and N. bengalensis apparently share a closer evolutionary relationship with each other than with members of their own species , possibly due to introgressive hybridization since the tested individuals of these two taxa originated from a region of sympatry in southern Thailand . This hypothesis was corroborated by a 2007 study that compared the variations in mitochondrial DNA sequences between N. bengalensis and N. coucang , and suggested that there has been gene flow between the two species . 
