Evo-Devo Doesn’t Really Explain Much

Doc Myers has another evo-devo post up; this one is on conserved dorsal-ventral patterning in the vertebrate and arthropod nervous systems. This stuff is fascinating, and Myers does a great job of explaining the research for a general audience. I’d imagine he’s an amazing teacher, as well. The entire field of evo-devo is really increasing our understanding of the evolution of animal body plans, with many more interesting discoveries on the horizon.

But it doesn’t really do much to explain evolution on a broader scale. Work in the field of evo-devo is mostly limited to animals, with some stuff being done in plants. Check out the eukaryotic phylogeny I posted a couple of weeks ago. Notice that animals (and land plants) make up a tiny fraction of the diversity of eukaryotes. Also, keep in mind that this tree excludes archaea and bacteria, the other two thirds of the diversity of life.

How significant can evo-devo be if it can only explain the goings on in a small subset of taxa? A far broader scope would carry much more importance — for instance comparative molecular biology or evo-cell biology. If you want to make truly meaningful comparisons, choose something that all eukaryotes (or, better yet, all cells) have in common.

Thanks to Larry Moran for bringing this up in the comments.


  1. #1 PZ Myers
    September 13, 2006

    This is a glass half-full/half-empty kind of argument, though. When someone puts together a teeny-tiny piece of the puzzle in one corner, is it reasonable to complain that there are a few million pieces of the puzzle left to solve? I don’t think evo-devo claims to have the path to all of the answers for all of life on earth: it’s a path to understanding the complexity of developmental interactions in multi-cellular organisms.

  2. #2 Carl Zimmer
    September 13, 2006

    I wouldn’t be surprised if research on microbes takes a evo-devo turn in the future as well. Microbes are not solitary critters, but parts of big social collectives that work together to form biofilms, gliding slugs, etc. They need the same coordination of gene expression over time as an embryo.

  3. #3 RPM
    September 13, 2006

    Thanks for chiming in guys. Check out Larry Moran’s comment. The issue is with evo-devo being hyped as a revolutionary approach toward studying evolution, when it only deals with a subset of eukaryotic taxa. And I agree with Carl that extending it out to microbes (ie, the majority of eukaryotes + prokaryotes) would definitely make evo-devo far more significant.

  4. #4 Timothy Chase
    September 13, 2006

    Evo Devo has a great deal to say about the evolution of multicellular organisms, and that is a great deal. Granted, they aren’t doing that much with single-celled organisms, but that would be a bit like faulting a mechanic for not being a good cook. It is a division of cognitive labor. They can show us how to get from single-celled eukaryotes and organisms like the social amoeba to the organisms which most common folk seem to care the most about (rightly or wrongly), but it is up to the microbiologists to study how we got from the most primitive form of cell to modern-day cells, and likewise, to identify the roles which microbes play in their interactions with other organisms, within ecological systems, and more generally, in the biosphere. However, this clearly won’t be possible without an understanding of the various roles plays by viruses, and most especially, the roles played by bacteriophages in their interactions with prokaryotes and archaea. There is a great deal of coevolution which has gone and continues at a breath-taking pace today.

    From a certain perspective, one may view modern prokaryotes as the cummulative result of an extensive process of tinkering by phages which have themselves adapted to and been radically altered by a shared ecology. There exists an extensive small-world lateral gene transfer network, where phages contribute gene modules, including pathogenicity islands, metabolic islands, symbiosis islands – and of course genes for resistance to antibiotics, including those being used by various species of bacteria throughout the larger part of the existence of life. As a result of this interaction, phages, in turn have become extremely modular, exchanging modules via bacterial intermediaries.

    There are many pieces to this, and there is a great deal of work to be done. Those in Evo Devo may have a slightly exaggerated sense of the importance of their own work. This is understandable – it is the natural result of the cognitive division of labor which exists in the biological sciences. But do not begrudge them their moments of glory. It is all part of a larger puzzle, and the work that they perform will highlight the importance of your own in the time to come…

  5. #5 razib
    September 13, 2006

    does biology have its own field when there is so many other physical processes in the universe? what about neuorscience having its own field, how come there isn’t liver-science?

    the universe is homocentric. so yeah, evo-devo isn’t all that, but when viewed in the context of human values of “what matters” it is quite a bit. the same critique of evo-devo i think could be made of biology as a whole by those boring physical scientists.

  6. #6 RPM
    September 13, 2006

    But Razib, evo-devo claims to explain evolution. If it can’t explain that for the majority of life on earth, it’s impact is limited. Biology does not claim to explain anything more than life. It shouldn’t be held responsible for not dealing with the things physics and chem deal with.

  7. #7 razib
    September 13, 2006

    evo-devo claims to explain evolution

    hm. can you point me to what you are talking about in terms of grand claims? i read sean carroll’s endless forms most beautiful, he seems more like the claim would be more that it provides an essential piece of the puzzle, that it is, it a step toward completing evolution. i don’t know if a head count of the number of nodes in the tree of life which are x is always so important. i agree that evo-devo practioners tend to grossly simplify, but language is really shitty at capturing the range of the parameter space of biology.

  8. #8 Vinzo
    September 14, 2006

    Evo devo is important, even outside of the limited field of animal evolution, for that it’s a different way of thinking about old things: a more dynamic one, actually considering the way organisms are built up to understand how they can evolve.

    Not completely a new idea though, since it’s nothing but truely dialectical biology… But important in the sense it shows that this method is effective, maybe the only effective one?

    It does not mean that Evo devo people have lessons to give to other evolutionary biologists. But since the history of ideas is mainly influenced by human centered/mammal centered/eukaryote centered views, a change for the best in this area should have widespread – and positive – consequences…?

    However, making too much noise about evo devo might not help ‘classic’ neodarwinians and population biologists to consider it seriously: this might just reinforce the view that it’s mostly ‘Much ado about nothing’.

  9. #9 RPM
    September 14, 2006

    Razib, my goal isn’t to take away from the great findings of evo-devo, but to put those findings in context when they deal only with animals. Carroll refers to it as “The Evo-Devo Revolution” in his book. How revolutionary can it be when it’s only on a small part of the tree of life?

    I think that the argument that evo-devo is important because it suggests a new way of thinking about an old problem is a good one. That’s why I like Carl’s idea of extending it out to other branches of the tree of life. But let’s not get ahead of ourselves.