Additionally they estimated the effective population size of the common ancestor of humans and chimpanzees to be ~ 100,000 . This was somewhat surprising since the present day effective population size of humans is estimated to be only ~ 10,000 . If true that means that the human lineage would have experienced an immense decrease of its effective population size ( and thus genetic diversity ) in its evolution . ( 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 ) . When three species are fairly closely related to each other ( like human , chimpanzee and gorilla ) , the trees obtained from DNA sequence data may not be congruent with the tree that represents the speciation ( species tree )
Toba catastrophe theory
Toba catastrophe theory
Human evolutionary genetics