Lynn Margulis has an interesting interview in Discover Magazine, where she puts forth symbiogenesis as the most important mechanism in marcoevolution.
I find her claims about AIDs implausible, to say the least.
Nonetheless, her arguments for symbiogenesis stand. I'd been aware of the way many organisms intertwined with others, but had never taken this to challenge evolution as tree shaped before. She's lead me to challenge much of what I'd taken for granted in evolution.
Natural selection eliminates and maybe maintains, but it doesn’t create.
The point is that evolution goes in big jumps.
Long-term symbiosis leads to new intracellular structures, new organs and organ systems, and new species as one being incorporates another being that is already good at something else. This major mode of evolutionary innovation has been ignored by the so-called evolutionary biologists.
The evolutionary biologists believe the evolutionary pattern is a tree. It’s not. The evolutionary pattern is a web—the branches fuse, like when algae and slugs come together and stay together.
From the very beginning the Russians said natural selection was a process of elimination and could not produce all the diversity we see. They understood that symbiogenesis was a major source of innovation,...
In 1924, this man Boris Mikhaylovich Kozo-Polyansky wrote a book called Symbiogenesis: A New Principle of Evolution, in which he reconciled Darwin’s natural selection as the eliminator and symbiogenesis as the innovator.
Sensory cilia did not come from random mutations. They came by acquiring a whole genome of a symbiotic bacterium that could already sense light or motion. Specifically, I think it was a spirochete [a corkscrew-shaped bacterium] that became the cilium.
If I’m right, the whole system—called the cytoskeletal system—came from the incorporation of ancestral spirochetes. Mitosis, or cell division, is a kind of internal motility system that came from these free-living, symbiotic, swimming bacteria.
This is the best explanation of the Pauling Effect I have come across. Saturday Morning Breakfast Cereal
I've been thinking about symbiogenesis in relation to memetics. Perhaps it will someday be extended to include the symbiotic relationship memes have with gene-based humanity. While memes relies on external host copying instead of a genome, memeplexes have an independent evolution as much as biological viruses do.
Here's a somewhat far-fetched implicit extension of symbiogenesis. It's one version of Gaia where all of us become so interconnected via the internet that we function together as an organism.