Scenarios where the lack of rival ancestors hurt gameplay enjoyment and immersion:
Loss of food source
A common occurrence when I evolve large motile predators, is that if I accidentally make them larger than the ecosystem can support, they are extremely successful as predators when young, but incapable of finding food whilst adult because they’re too slow. Whilst it’s fair that I should go extinct if I was operating as a lone example of my organism, it can become extremely aggravating if the young of this species is thriving at first and numbers in the dozens on screen at any one time.
Having ancestors that stick around would solve this issue because the slightly smaller consumable predators from the previous turn can act as a food source for the larger adult population of my new species, allowing for a transition into apex predation by eating the young of that species. In evolution, if a predator becomes unable to consumer the smaller producer organisms of their environment for what ever reason, but still is surrounded by lots of biomass in the form of smaller examples of itself, the predator will shift into a diet of it’s ancestor, which will in turn evolve to become a smaller generalist. For a real life example, fish species that become too large to eat smaller organism will instead turn to their recent ancestors, and get larger and bulkier to consume those instead as a main food source.
The lack of any way to consume larger predatory organisms that become common by eating smaller faster organisms, means that thrive possesses no wat to make a transition in food source when the previous food source becomes scarce or unattainable by happenstance. I cannot tell you how aggravating it is to have no source of food as a large adult predator, but constantly bump up agaisnt smaller, engulfable examples of your own species that have proliferated the environment.
No adaptive radiation
One weird thing about thrive in it’s current form is that evolution seems to be sporadic, random, and almost as if creatures emerge from nothing all of a sudden. This is because autoevo seems to spawn new species into the simulation wholesale, without much relation to species that already exist in the game world - For example a few times, on the second turn I will see enormous cells spawn in comparison to my own starter species, or in an environment comprised mostly of small photosynthesizes, a massive predatory organism with toxins might arrive that has no relation to the existing organisms.
Maybe this is an aspect of autoevo pulling from other hexes, or maybe a deceptive use of cytoplasm that makes it loo larger than it should. But either way, it leads to an experience that is perceived as being random, not continuous, unrelated to progressive diversification, and it especially feels unrelated to your own organism’s evolution with creatures instantly shapeshifting into forms that seem alien and unrelated. This is especially bad in relation to the circumstance that this section is about, specifically adaptive radiation in the scenario that a patch-based local extinction event occurs, or when you first join the game and other species are supposed to radiate out from your own.
In the context of starting the game, adding ancestors that remain in the game world as rival species will increase how much it seems like you are competing for the first stable niches, and increase how fun it is to race towards the available cloud-like resources. In the early game it can be quite easy and boring to evolve your creature into the first few iterations because there is no competition for resources. This is especially obvious when replaying the game, and that part of the experience might as well be removed in terms of actual gameplay because there is no skill involved.
In the context of responding to extinction events on the other hand, it can seem weird for species to vanish, but then fully formed species to move into the patch and take their place with no context for where came from or how they evolved. In the gameplay which is where such info matters, evolution can seem random and that makes it feel unfair if you are outcompeted by these seemingly random new species and go extinct. By allowing ancestors to stay around and slowly fill niches by adapting over time, it reduces the amount of out of context invaders that can arrive to instantly fill extinct niches, and also allows players to see the progress of radiation and how these species adapt and change to suit their environment.
The final context in which ancestor survival helps adaptive radiation seem more visible, is if the environment changes around you in such a way that there are multiple niches that your species can fill, for example either a stronger predator, smaller herbivore, a generalist, etc, and any of those choices would be correct in the context of evolution. The saying “evolution abhors a vacant niche” is important here because realistically, there should be a massive adaptive radiation of your own organism into various similar niches based on what is vacant in the environment. Currently in the game, the environment has this weird situation where the player lineage only fills a single niche, and any AI species adapted from it become either massively different to the point they aren’t identifiable as from the same lineage, or go extinct.
By having ancestors stick around and compete for your current niche, you will see various descendants of the two competing species enter their own niches later on, by diverging more realistically. You will be able to watch as species derived from you slowly change to fill environmental niches, and then eventually after many turns, they are their own distinct lineage with their own relatives and offshoots, and you can see visibly how an example of what you made slowly changed to fit into the ecosystem alongside you, in a different way.
Final thoughts:
So far, the only major reasoning to disable ancestor survival is that the players ended up swamped by their own species in their environment, which reduced ecological diversity. However, Nie’s idea to make ancestor retention tied to species name changes gives control of this mechanic to the player, and allows them to strategically deploy ancestor retention only when it would be beneficial to the gameplay experience. It effectively lets players choose their preferred playstyle whilst designing the species; Those that prefer an experience more similar to thrives current state would change their name less often, whereas those who wish to see a world more filled with offshoots of themselves will change their name more often. Or maybe the feature could be turned off entirely if a menu option is clicked?
Overall, i think that this feature is a vital component of evolution that becomes more conspicuous in it’s absence the longer it remains out of the game. A vast majority of IRL speciation occurs through competition with ancestor organisms, or related descendants of ancestors. Imagine how the world would have turned out if stingrays never competed with sharks, or octopus never competed with squid, humans never competed with neanderthals, or lizards never competed with snakes, etc. In fact, i’d wager that this is such a large aspect of the conventional evolution process that if it’s not implemented into thrive early on, multicellular and macroscopic sections of the game will end up being way less realistic than they should be, and the long term gameplay experience will suffer.