I was going back and forwards with eco games for years. Been building some simple simulations, with different tools over past years. But just now, with DOTS, it struck me, this may be actual something interesting and possible to build.
I have played multiple prototypes of different peoples, so I see how they approached such problems, I will be facing. None however I have seen, had placed whole thing on a sphere.
For now gene mutation is rather simplistic. I didn’t went for sexual reproduction, but rather asexual. Just like cell divide. Weather I will go for sexual reproduction, by mixing DNA, I am not sure yet. Definitely mutation would then be, within group of similar specie.
However, now mutation is done on randomization of each gene. Game can mutate each individual gene by increasing or decreasing properties. Or order to not mutate. By default direction of mutation and the factor is random within a permitted range. Each new offspring is mutating.
I want player, to be able have certain degree of control, on mutation of selected group. Then allow evolve
I was thinking recently, to add at some point brain and neural networks, for intelligent species. Then they will learn by evolving. But that may be still ahead I got algorithm for NN anyway, which I was working before and can teach at runtime by players. I don’t use Unity tool, which is python bonded. However, first, I would go with simplified mechanics, using Utility AI as per discussion in attached thread.
How I will approach this problem not sure yet. I got tons of idea, but I focus only on immediate steps, to not go astray with, too far 
Social behaviours would something cool. Like flocking etc. If I use boids algorithms and NN brains, I think that pretty feasible.
Another thought, but rather difficult at this moment, is to make plants being able to grow, something like trees. But I may just stay with simplification, of height. If I could come up with better DNA structure, I could mutate anything with anything.
Also, I may actually voxelise species. For example, instead base structure of creature / plant to be a mesh, to be blocks. Then I could create some interesting formations. Tree could for example loose branch, or gain a branch in next generation mutation. Animals could have more / less motor mussels, allowing movements. All in simplified form of course. Maybe I will make kind of each voxel as relevant functional cell. But again, I would need have redefine DNA concept. For now, I am not marching in this field. But is heavily in my mind.
At current, herbivores can technically be also plants and vice versa, if they got relevant genes, to generate food from the sun. Plants produce food faster, but metabolism is generally slower. That however can be enhanced by relevant mutations. In fact, sun position affects photosynthesis. In night there is none. Movement will cost energy. Is not yet implements.
Greater challenge is, how to make sure that plants / animals hybrid are not too OP
I need figure out some sensible penalties system. Photosynthesis is good step toward direction.
Another though is, since I don’t consider using shadows as factor for reduced photosynthesis, how to give benefit for plants, to grow higher. I could take just higher plant, then it become more efficient. That kind of sort I got now. Then kind of grass, which is low and flat, but wide. How can it get good benefits.
These all are thoughts of course. Some may just stay as thoughts.
On side note, planets on vids are between 15 to 25 radius. I hope with DOTS, to allow make them bigger, to be able populate planets. If species can evolve bigger, then could expect have pretty big creatures / plants there.
On side note 2, by default, I am not allowing for cannibalism. Saying that, if DNA difference is close enough to the threshold, then life form is treated as same species. But I plan also add this factor to DNA pool. Is just not linked yet.
Edit:
I think I have figured out, how I could make cellular/voxelized based DNA 
I will grab some concepts from my Hovercraft projects.
