With the genome of the western gorilla, authors Aylwyn Scally et al have contrived very successfully to contrast ourselves and other ape genomes as they have changed in evolution. In Nature, they reveal a speciation away from the chimpanzee line 6 million years ago and a ten million year gap since we speciated from a gorilla line.
There has even been a parallel evolution involving genes for hearing. The gorilla speciation shows that east and western groups must have separated 1.75 million years ago, although there has been some interbreeding, as might be expected.
a) Distribution of gorilla species in Africa. The western species (Gorilla gorilla) comprises two subspecies: western lowland gorillas (G. gorilla gorilla) and Cross River gorillas (G. gorilla diehli). Similarly, the eastern species (Gorilla beringei) is subclassified into eastern lowland gorillas (G. beringei graueri) and mountain gorillas (G. beringei beringei). Areas of water are shown pale blue. Inset, area of main map.
b) Western lowland gorilla Kamilah, source of the reference assembly (photograph by J.R.).
c) Eastern lowland gorilla Mukisi (photograph by M. Seres).
d) Isolation-migration model of the western and eastern species. NA, NW and NE are ancestral, western and eastern effective population sizes; m is the migration rate.
e) Likelihood surface for migration and split time parameters in the isolation-migration model; colours from blue (minimum) to red (maximum) indicate the magnitude of likelihood.
Scientists in the past have created controversy with their references to our close similarities to other hominids. However they were correct. It seems we aren't that much further from gorillas than chimpanzees, although orangs are much further down the tree!
a) Here the orang-utans appear on the right (O), speciating in the Middle Miocene, and H,C and G are humans, chimpanzees and gorillas, reading from the left.
b) The five fossils mentioned are - The lower bar shows human mutation rates such as European (CEU) and Yoruban African (YRI)
The challenge for the many authors involved was, apart from the collaboration, to assemble a complete genome, including three gorilla species for which little data was available. The present-day isolation of the gorillas means we don't really appreciate how genetically-related they can be. In the past fossil great apes must have mutated at different rates, just as humans mutate less now. Sahelanthropus and Chororapithecus are almost impossible to relate to either gorilla or man unless the rate decreased early in evolution. This lack of ability to actually observe past rates of mutation leaves some uncertainty. For example the range for gorilla/human split could be from 8.5 to 12 mya. Sivapithecus looks a likely lad, lasting for a long period in the fossil record, before his sad loss. We can do with such persistence nowadays!
With Homo virtually extinct as a genus, it seems almost a shame we can't go back virtually to the Middle Miocene and observe the great apes of Eurasia and Africa at the time. These apes have been dispersed and fragmented since that time, but the cruel processes involved may have led to our own success. We had our crises too, similar to the current conditions of the other great apes. In 100,000 years one species has bucked the trend, we know not how. Three of the other genera definitely exchanged genetic material (cross-bred), helping them survive, so it is a possibility that Homo sapiens was subject to the same solutions for survival as these survivors. But survive, at some others' expense, we certainly have.
It's now our responsibility to ensure a solution for the sure survival of these wonderful endangered relatives, by every means at our disposal.
The threats they face are now purely from us.