Some solid ideas there, and let me say how I see those analogies play out in blockchain tech: Forking is still the current way to make radical changes (biological evolution). Smart contracts are the current analogues to the cultural evolution you talk about.
In theory, any improvement implemented via a smart contract can be implemented via a fork, and from a technical perspective (speed, memory efficiency) the forked implementation can be designed to run better.
But smart contracts do have on major advantage, and that's a political one: smart contracts because of the sand-boxed nature in which they execute (assuming no bugs in your smart contract processing code) enable new functionality to be added to a cryptocurrency network without requiring consensus to add the new functionality (only people who want to participate in the smart contract's new rules need to care about it, everyone else using the blockchain can ignore it). And here we see the analogy to cultural evolution when looking at smart contracts: changes can be made on a smart contract system without requiring change to the base platform (the DNA, so to speak). With a smart contract, you "teach" the existing blockchain how to do new things without making a low level change to how it operates.
Steem doesn't have smart contracts of this sort currently, and it would require a hard fork to add them, but it's certainly doable.
There's also another alternative to smart contracts as a means of evolution without requiring full consensus and that's by linking up chains via trustless crosschain transfer. Then users can transfer value between networks with differing rules, enabling them in many cases to obtain the benefits of multiple blockchains. This could be viewed as cultural evolution, or maybe it's more like "emergent behavior" (it's easy to stretch any analogy too far). But in any case, it's a way to enable new behaviors on a blockchain without changing it's DNA.
As a side point, note that "trustless transfer" technology is different from atomic crosschain swaps (although they commonly get conflated with each other), it's a different and more powerful technology, which to my knowledge has not yet been implemented for any pair of chains. But it's definitely theoretically possible and I expect to see someone do the hard work eventually.
But to achieve all the evolution of rules that I think we need to see in consensus technology (a term I'm coining now that is similar to what people call "blockchain technology", but only requires consensus mechanisms and no actual blockchain) I believe the performance advantages of hard-coded rules will be needed for some time to create technology that operates at sufficient speed to solve some important problems.
In a perhaps an ironic twist, my own primary area of interest is looking at ways to use consensus technology to speed up the rate of our human cultural evolution.
Yeah, so the primary thing of concern seems to be how much the consensus technology (seems like a good term) can allow for different groups of people to meet their needs - the political aspect you talk about. One size does not fit all, so people have to be able to create their own rules and arrangements to suit their own needs. As you say, smart contracts allow for this since only people who opt into the smart contract are using it (i.e. we assume everyone else is pretty much unaffected, or they are affected (everything is connected to everything else from a systems science perspective) but to such an indirect and low extent that it's acceptable).
In the case of Steem, it seems that SMTs + Communities would allow for quite a lot of this - different groups making up their own rules without interfering with the other groups. It seems to me like the Steem base layer is allowing for lots of such cultural evolution.
What you say about inter-blockchain trustless transfers also seems quite interesting and I wonder how much it can be implemented with TRON and Steem. Any thoughts?
With regards to the evolution of design, I guess my overall point was that the Steem community can make progressive hardforks, as it has done many times, but the community remains as a single whole. There doesn't have to be a split in the community since the entire community accepts the evolution. It seems that this evolution of the base layer through hardforks is about smart ways of increasing flexibility so as to allow for cultural evolution to happen and groups to come up with their own tailor-made cultural rules.