I have spent the past 10 months working on an ideation that details the Pan-Homo split, which was caused by introgression from Gorilla. I'm very happy with the work, publishing has been arranged, and it is also secured with "proof-of-thesis" on Ethereum, EOS and Bitcoin, in short, the state of consensus technology at this point in time.

You can read it in full over https://peerj.com/preprints/27163/, a "preprint" is in that it is not recognized as having been recorded in time ("print"), and, for an introduction to proof-of-thesis, read more here.

Why are humans eusocial?

The thesis described above is foundational in a broader ideation I have worked on, that maps the fossil record in Afar to the rotation of the Danakil block (read more here) and I chose to focus my resources on proving it first as it is very conclusive evidence for that broader ideation.

You can see below that if the thesis is correct (which it is, tough that will be proven by the results being reproduced, over and over again, independently by other people such as yourself), and, if the proposition that the fossil record in Afar follows the rotation of the Danakil block is correct, then, you can see for yourself that it explains a lot.

Edward O. Wilson describes humans as eusocial, and, once you see that, you cannot un-see, humans have a social organization similar to insects, they are mediated beings performing complex societal functions through division of labour.

What exactly was it that triggered the evolution of eusociality in humans?

The "companion-species" hypothesis

As I prove in the thesis here, and, if I am correct, which I am, then you will see the results be reproduced by other people, you yourself for example, the introgression from Gorilla led to two hybrid lineage, Paranthropus and Australopithecus. That is a bold statement, and do read the proof I have produced, and also try and reproduce the results, I am not interested in spreading false narratives and it is in my self-interest to be falsified if I am wrong.

These two lineages follow one another, as in, they exist within the same regions, from the Pliocene into the Pleistocene. What the idea I had was, a very very different idea from anything I had heard before, was that the more intelligent of the two species, that later evolved into Homo (possibly by introgression from Paranthropus as you see the same teeth morphology appearing in Homo), domesticated the other, and that the two lineages formed a two-species society, in the same way ants have worker ants, queens, and soldier ants.

Technology extends the phenotype beyond the gene pool, but initially, a two-species scenario would also do that. The wheel is an anatomical extension, a horse is as well. They are equivalent in extending the capacity of Homo. A two-species society also requires skills similar to the skills needed to use technology, to understand an external object or another being in the same way you understand your own body and yourself.

In the "companion-species hypothesis", the inherent division of labour between Homo and their companion-species would have formed a natural hierarchy, that introduced a favourable environment for the evolution of eusociality, as well as Theory of Mind (ToM).

I do not really like the word "speculation" because I have had ideas that are proven be called speculation, simply because the other person was too pre-occupied with their a priori prejudice and would not even look at the evidence, but, this idea is very much speculation.