Fossil candidates like Sahelanthropus tchadensis, Orrorin tugenensis, and Ardipithecus ramidus have been debated as either being early hominins or close to the CHLCA.
Mann and Weiss (1996), proposed that the tribe Hominini should encompass Pan and Homo, grouped in separate subtribes.
)[2] A "chimpanzee clade" was posited by Wood and Richmond, who referred it to a tribe Panini, which was envisioned from the family Hominidae being composed of a trifurcation of subfamilies.
Sahelanthropus tchadensis is an extinct hominine with some morphology proposed (and disputed) to be as expected of the CHLCA, and it lived some 7 million years ago – close to the time of the chimpanzee–human divergence.
[11][12] The earliest fossils clearly in the human but not the chimpanzee lineage appear between about 4.5 to 4 million years ago, with Australopithecus anamensis.
[17] A 2016 study analyzed transitions at CpG sites in genome sequences, which exhibit a more clocklike behavior than other substitutions, arriving at an estimate for human and chimpanzee divergence time of 12.1 million years.
Different chromosomes appear to have split at different times, possibly over as much as a 4-million-year period, indicating a long and drawn out speciation process with large-scale gene flow events between the two emerging lineages as recently as 6.3 to 5.4 million years ago, according to Patterson et al.
[23][24] Such a scenario would explain why the divergence age between the Homo and Pan has varied with the chosen method and why a single point has so far been hard to track down.