(see Toba catastrophe theory)

Another study (Chen & Li, 2001) sequenced 53 non-repetitive, intergenic DNA segments from a human, a chimpanzee, a gorilla, and orangutan.When the DNA sequences were concatenated to a single long sequence, the generated neighbor-joining tree supported the "Homo"-"Pan" clade with 100% bootstrap (that is that humans and chimpanzees are the closest related species of the four).