Here is, I think, conclusive evidence of gene transfer from Gorillae to gracile Australopithecines 3 million years ago. The data that is interpreted as deletions here, is gene transfer from the gorilla lineage to the human lineage, which then did not transfer to chimpanzee, resulting in the same genome sequences as deletion.

The corresponding analysis for deletions shows a markedly different pattern, with the rate occurring in a more clocklike manner throughout most of the tree with the notable exception of the ancestral lineage of chimpanzees and bonobos. We observe an approximate twofold increase in the rate of deleted base pairs leading to a distortion specifically along this branch (P = 4.79 3 109 ).
Evolution and diversity of copy number variation in the great ape lineage (Sudmant, 2013)

Sudmant et al ties the absence of 59 genes in the chimpanzee-lineage to a population bottleneck 3 million years ago. Within an interbreeding model, that deletion was instead gene transfer from the gorilla lineage to human lineage, and vice versa, resulting in the same genome sequences, and set at 3 million years ago, at the time of the Pthirus gorillae host switch (Reed et al, 2007)

This increase results from an excess of large (>5 kb) chimpanzee–bonobo ancestral deletions, which affect significantly more genes when compared with all other great ape lineages (Fig. 4C) (P = 4.397 3 108 ). Notably, this excess of deletions corresponds to a predicted collapse in the ancestral chimpanzee–bonobo effective population size (Ne) ;3 mya (Prado-Martinez et al. 2013; Supplemental Section 5).

Empirical evidence of the "companion-species" hypothesis for the origin of eusociality in humans

I put out the "companion-species" hypothesis the other day, as a model for eusocial evolution in humans. Humans are the only mammal that are eusocial.

https://en.wikipedia.org/wiki/Eusociality

The idea is that the Pthirus gorillae host switch, which Reed et al put at 3.3 million years ago, was the result of interbreeding between Au. afarensis and gorilla ancestors.

Paranthropus appears in the fossil record around that time, and would be a hybrid (therefore, the gorilla-like sagittal crest and so on. )

Paranthropus are found along the rift valley where Homo is also found

"The cave was discovered in 1948, and initial excavations were carried out by paleontologist Robert Broom. His team uncovered several remains of Paranthropus robustus and early Homo species. It was the first site at which both Paranthropus and Homo had been found together, indicating that they were contemporary.[4] "
https://en.wikipedia.org/wiki/Swartkrans

References

Pair of lice lost or parasites regained: the evolutionary history of anthropoid primate lice (Reed et al, 2007)