Thanks for posting the better chart for me. The description is found somewhere in the middle of my Comment #54. Green is human, red is Neanderthal, and blue is chimp.
If, in fact, bonobo divergence from chimp occurred at a very specific time, that raises an interesting question. Is there a gene or cluster of genes for sexy behavior that we both mutated to, or was there something different about the bonobo environment and our own that caused a different evolutionary path than that of the other chimps?
I think it was just something that ‘worked’ for them - who knows what the more ancestral trait was - hard to tell.
Human sexuality is about the pair bond - thus the face to face - the enlarged sexual display at the front of the female, etc. Also the females and males of our species are very close in size - which is a good indication of a pair bonded species - the larger a male is in proportion to the female the larger the expected “harem” size each male will achieve. Our testicle size in proportion to our body size is compatible with our pair bond - but with a ‘crypto-paternity’ rate of 10%; while both species of chimps have large testicles to represent their promiscuity among the band - gorillas are much smaller (harem) - gibbons as well (pair bond -100%).