The human genome was sequenced in 2001, followed by the chimpanzee in 2005 and the gorilla in 2012.^[1]

The standard view of the great-ape family tree is that humans and chimps are more similar to each other than either is to the gorilla — because chimps and humans diverged more recently. What the gorilla genome project showed was that 15% of human genes look more like the gorilla version than the chimp version.^[1]

This is often explained by incomplete lineage sorting (ILS), that the last common ancestor gene pool has been inherited that way. Another explanation, is an hybridization event 3.3 million years ago, giving rise to the Paranthropus lineage, explaining the host switch of Pthirus gorillae to Au. afarensis pubic hair,^[2] which happened at that time, and those 15% gorilla genes within the human genome that were discovered only 5 years ago.^[1]

The Paranthropus lineage as a Au. afarensis — gorillae hybrid

The Paranthropus lineage dates back to around 3 million years ago, to die out some 1–2 million years after that.

The host switch of Pthirus gorillae to the pubic hair of Au. afarensis is dated to 3.3 million years ago.
In 2012, a study of the gorilla genome showed that 15 percent of the human genome is closer to gorilla than chimpanzee.

Was there an inter-breeding event around 3.3 million years ago, giving rise to the Paranthropus lineage, as well as transfer of some genes to what became the Homo lineage?

References

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

Insights into hominid evolution from the gorilla genome sequence (2012)