(Picture from here.)
Here’s a very good article on the evolution of the animal developmental process. It’s not so good at explaining plant embryogenesis (wikipedia article here.) If you followed the articles conclusions, plants would be a form of degenerate animals since they also have embryogenesis. I’m not going to go into it in this post but I suggest reading it.
My own suspicion is that the process of multicellular organization that led to the evolution of development probably predated either plants or animals. The organizational principles might have been in play (see Volvox for example) but the actual process of developing embryogenesis likely have evolved separately between the plants and animals. When I read about it I see little similarity other than the fact that both higher plants and animals have a definable pattern of developing adult organisms from dissimilar embryonic precursors.
The evolution of fungal life cycles and that of slime molds likely also have evolved separately. Fungi look like they have evolved from animals or at least an animal precursor. (See here.) There is some genetic evidence that the gilled mushrooms and puffball fruiting bodies may have evolved fairly recently and may also have arisen separately as many as four times. (See here.) What’s less clear is how fruiting mechanisms of fungi evolved at all.
Slime molds (Myxomycetes) are interesting in that they have a single celled form and a multicelled form. When they mate they form a plasmodium, a large structure consisting of nuclei without any intervening cell membranes. The plasmodium then extends itself (and sometimes appears to actually move) by cytoplasmic stream and consumes the food source. When the food source wanes, it forms a fruiting body that looks mushroom like and develops spores.
These sorts of strategies are important in Science Fiction. SF aliens even in their most extreme form are usually animal in nature. There are a few exceptions: the living planet in Stanislaw Lem’s Solaris. And the microbial gods of of Ken MacLeod’s Engines of Light trilogy. SF Plant intelligences are essentially animals in plant suits. (See here.) Which is only marginally better than humans in alien suits.
It doesn’t have to be that way.
I’m a big fan of using the strange and wonderful biological world of earth as inspiration for alien worlds. And, certainly, the animal kingdom is filled with the truly strange and completely non-human. But I’m also among the first to admit that this is animal chauvinism.
We have no idea of the shape of life on other worlds. I think we can suggest that if there are the ingredients and opportunity for a carbon based origin of life that life will in fact arise. And we can further speculate with evidence that the result will go as far as a similar metabolic path as earth’s: using light to fix CO2 into carbon polymers and thereby releasing oxygen and metabolizing the resulting organic compounds in the presence of the resulting oxygen. Note the caveats: it says nothing about non-carbon life. We can’t even say that life has to take a cellular path– there are some very interesting experiments involving organic compounds unconstrained by chemical cells but constrained by physical components such as the cavities in lava rock. Or that individual cells are the preferred path. The slime mold plasmodium mentioned above is fairly large– sometimes meters across– and has no cell membraines. It is, in effect, a single cell.
We have no idea what things are like out there.We know only a little more about what things are right here.
The stories we want to tell are about human beings. Aliens are one wrench in the tool chest writers can use to tinker with the human experience and see how it works. This is, in my opinion, one of the distinctions between SF and fantasy. SF has at least the toe of one foot in the world we live in, the world of thermodynamics and the Cretaceous. Fantasy does not need that toe. In a fantasy world we can have creatures that pursue evil for no reason except they’re evil. In the SF world, evil villains at least have to pursue evil because it makes them look cool. This is a technical evaluation not a judgement of quality. It’s just a distinction. A work of fantasy does not have to conform to physics though it may choose to. A work of SF is informed by physics even if the physics are ignored.
I’ve been talking about biology for a bit now. My intention is not just to say Look at that! Isn’t it cool? though that is certainly true. Instead, I’m saying that the biological world can serve as a tremendous well of metaphorical construction. Along with history, anthropology and archaeology, biology can help determine motivations, develop character and make stories.
Even with slime molds.