Last year, I argued that fungi are often excluded from conversations about the evolution of multicellularity (“Fungi are weird“):
Whenever we’re looking for commonalities among the various origins of complex multicellularity, commonalities that might suggest general principles for the transition to multicellular life, the fungi tend to either buck the pattern or provide an ambiguous fit. I have to admit that when fungi come up in these discussions, I have an unfortunate tendency to say “Who knows? Fungi are weird.” However, if László Nagy is right that complex multicellularity has arisen 8-11 times within the fungi, we might fairly say that the fungi include most origins of complex multicellularity. If so, maybe it’s not the fungi who are weird. If fungi truly include the majority of origins of complex multicellularity, fungi are the norm. Maybe it’s the rest of us that are weird.
I have finally gotten around to reading Maureen O’Malley’s Philosophy of Microbiology, which argues that any comprehensive theory of evolution needs to account for microbial life, life that often evolves in fundamentally different ways from the plants and animals on which most of the theory has been based. She makes a related, but broader, point:
No special account of evolution need be given exclusively for microbes, but any general theory of evolution needs to accommodate the greater range of evolutionarily relevant activities in which microbes participate. Perhaps this is also the place to make a plea for other organisms that have so far been invisible to the philosophy of biology, such as the enigmatic fungi. Although more closely related to animals than any other major clade, fungi have not featured prominently in either mainstream evolutionary theory or philosophical analyses of such theory. Looking at gaps and neglect is not an exercise for its own sake, but a constructive project: to work out how the current framework stands when confronted with apparently anomalous and wayward organisms. –p. 129
I couldn’t agree more. Animals and plants are special cases, with features such as an alternation of haploid and diploid generations, (usually) obligate sexual reproduction, and (in some cases) early germline segregation that have major implications for the way they evolve. Much of evolutionary theory, the standard models of population genetics and quantitative genetics for example, has taken these lineage-specific features as starting assumptions. A truly general theory should apply to all of life, with animals, plants, fungi, microbes, and even viruses treated as particular cases within the larger framework of the theory as a whole.
Does anyone say that “the” theory of biology is incomplete, unless it explains chemistry and physics? Does anyone serious say that the electroweak or chemistry theories are incomplete unless they explain biology?
I think it is reasonable to say that the standard theory of evolution has only ever been talking about multicellular life that has a sexual aspect to reproduction. Thus, different theories are needed to cover abiogenesis and to cover the changes in life between these stages. I see no urgent need to have one unified theory that addresses all of these at once, any more than a need to think of physics and biology as needing only to be analyzed in unified terms.
Maybe some future insights will justify some unifying, but for me it will be fine if I am patient enough to wait for it to come up naturally.
Matthew Herron says
A closer analogy is that we do say physics is incomplete because while we have theories that work within particular domains, we don’t have an overarching framework that unites them.
I’m a mathematician, not a biologist, but my PhD thesis was about mathematical models describing the tip growth of hyphae.
Simply describing the “humongous fungus” ( https://en.wikipedia.org/wiki/Armillaria_ostoyae ) was usually a great attention grabber if I gave a talk at a conference (for the mathematicians at least, I’m sure many biologists were like “yeah… sure, we knew that!”)
It basically taught me that a lot of the things I learned in AP biology in high school were ‘sometimes wrong’ for fungi, no clear cell divisions, cell nuclei freely floating around and crossing septei, things like that.
All models are wrong, and in this case for the evolutionary model, fungi are the exception to the rule. They don’t fit really well. I’m not sure if there’s a consensus whether the humongous fungus (or any other fungi) is even a single organism, a single cell (or perhaps only its mycelium is), a colony, or something different, and it raises the question *what* actually evolves here.
(Disclaimer in case some nutcase reads this: I’m not saying fungi don’t evolve… They clearly do, and we understand many of the processes behind it, just the standard theory doesn’t fit very well and may need some minor tweaking…)