I would be interested to know why the argument doesn't apply equally to unicellularity.

I apologize for a misunderstanding. My argument was not that one should "expect [their] successors to return to skullcrushing." It is that, as skull-crushing was an essential part of our evolution, it makes sense that we still have that latent impulse. Think sex.

I ... have never crushed anyone's skull for power and wealth ... and I'm not sure I know anyone who has

The people who actively "skull-crush" for power and wealth are largely tribes of people in the third world. This is occurring in many parts of Africa and some parts of the Middle East. This is where they do not enjoy the same quality of a first-world life as you or I do. Sure, you may not do any skull-crushing. You live a life which is pleasant enough, and the propagation of your lineage is guaranteed enough (and if you do not wish to bear fruit, so to speak, this is another indicator of the pleasantries of the first world). This is missing the point.

So at least within my nice liberal middle-class bubble -- which is, y'know, actually a pretty big bubble, encompassing a substantial fraction of the population -- the "joy of crushing one's enemies" seems not to be much of a thing any more.

First, it's not a large bubble given total human population. It is in fact quite a small bubble standing on the shoulders of violent giants. Maybe we should leave this bubble from time to time.

Second, the joy of crushing you enemies is still innate, as you state yourself ("if you allow for metaphorical crushing ... then there's more of it about"). Just as sexual reproduction leads to competitively viable organisms, leading to our innate desire for sex (even without the explicit desire to reproduce - another wonder of our first world) , violent competition led us to the point we are now. Can you say that you do not enjoy your doses of "metaphorical crushings"? Would you say that, in a doomsday-scenario, the use of violence would be a competitive advantage? If so, then surely some are utilizing it. They would have the advantage. They would reproduce (whether consensual or not - yet again a modern world invention). And we return to our forebears, and the latent spirit of violence lying beneath the surface of our civilized lives...

I digress. I'm not implying that all acts of our ancestors are needed today. I am stating that, no matter one's personal experience with violence, their existence has benefited from previous acts of violence. To state that these impulses have left us is false.