Everything old is new again

If you’ve ever invited me out to give a science talk, you know that what I generally talk about is this concept of deep homology: the discovery that features that we often consider the hallmarks of complex metazoan life often have at their core a network of genetic circuitry that was first pioneered in bacteria. What life has done is taken useful functional elements that were worked out in the teeming, diverse gene pools of the dominant single-celled forms of life on earth and repurposed it in novel ways. The really interesting big bang of life occurred long before the Cambrian, as organisms evolved useful tools for signaling, adhesion, regulation, and so forth — all stuff that was incredibly useful for a single cell negotiating through space and time in a complex external environment, and which could be coopted for building multicellular organisms.

But if you don’t feel like flying me out to tell you all about it, Carl Zimmer has an excellent article on deep homology in the NYT, and he uses a new example I’ll have to steal: a genetic module that we use to regulate blood vessel growth that can also be found in yeast cells, where it is used to maintain cell walls.


  1. Mike in Ontario, NY says

    This calls for a funeral and final burial of irreducible complexity. I shall dance on the grave.

  2. MolBio says

    It’s not dead until I’ve parodied Ray Comfort with some of my infectious diseases study:

    “Behold, the creationist’s nightmare, a mushroom!

    It has a NAG NAM cell wall like a bacteria, but a genetic system like a human, along with a mitochondria like a human.

    Some pathogenic and invasive, and trying to treat it is potentially lethal to the host because of their common eukaryotic descent. :p”

  3. MolBio says

    Sorry, it’s only N-acetylglucoasamine, (NAG) in cell wall (like a bacteria still though).

  4. martha says

    Good article as us non-science people can even understand it. I liked how it mentioned eyes as the eye is one of the things creationists argue cannot have evolved.

    Love the guy’s shirt.

  5. abb3w says

    MolBio: “Behold, the creationist’s nightmare, a mushroom! […]

    And, like a creationist, it flourishes when kept in the dark and on a diet of bullshit?

  6. thecwblog says

    This idea of disabling genes that send blood to tumors, could this be a universal treatment for cancer? Not a cure persay, but would it be a treatment used for all cancer types?

  7. MolBio says

    @ Theewblog: Perhaps. Cancers not only lose repression of cell proliferation and gain cell proliferation promotion mutations, but they also rely on inefficient anoxic metabolism. Therapies blocking anaerobic metabolism in tumours were having some good effect. In order to survive rapid proliferation accompanying angiogenesis mutations allow for tumours to create networks of blood vessels to feed them. Maybe a combination metabolism and angiogenesis targeting therapy could be a fantastic new treatment.

    @ Abb3w: Poetic justice, isn’t it? :p

  8. NewEnglandBob says

    I am re-reading Dawkin’s “The Blind Watchmaker” and had recently read the section on deep homology.

  9. Carl Zimmer says

    Cambrian??? Oh, PZ, you metazoocentrist! Step back to the Paleoproterozoic, where the real fun happened.

    (In all seriousness, thanks for the link love.)

  10. Midwifetoad says

    The really interesting big bang of life occurred long before the Cambrian

    Kind of what you’d expect with 6/7 of life’s history erased.

    Not to hijack the thread, but the other thread on alien life is somewhat relevant here. Any alien biology introduced would probably just be food for indigenous microbes.

  11. PZ Myers says

    But Carl, that’s what I said — all the interesting stuff happened long before the Cambrian.

  12. SaintStephen says

    Yup. Evo-Devo is incredibly fascinating, but deep homology is by far the coolest thing about Evolution. It just beggars the imagination; IMO it makes Evolution much more interesting than even Cosmology and Quantum Physics (and I love those topics, too!). BTW sorry about the selective capitalization for emphasis. My “gods” deserve formal names.

    Some day in the not-so-distant future, I truly believe these demonstrable facts of our existence, excavated scientifically by the thousands of dedicated genome researchers, will be what turns the tide for the New Atheists. Deism may survive intact, but the Big Three Institutions of Theistic Delusion will be reduced to hollowed-out Halloween pumpkins, rotting on the front porch in the first weeks of November, waiting for the final insulting kicks to their faces.

    As an aside, it also seems inevitable that some enterprising programmer, once enough data has been published, will be able to write one hell of a computer game based on deep homology. I wonder what kinds of weird new simulated life forms will evolve…

    Lastly, a good friend of Professor Myers waxed eloquent (Oh so damn eloquent!) on this topic a while back:

    There would be plenty of time for improvement. What weird engines of self-preservation would the millennia bring forth? Four thousand million years on, what was to be the fate of the ancient replicators? They did not die out, for they are past masters of the survival arts. But do not look for them floating loose in the sea; they gave up that cavalier freedom long ago. Now they swarm in huge colonies, safe inside gigantic lumbering robots, sealed off from the outside world, communicating with it by torturous indirect routes, manipulating it by remote control. They are in you and in me; they created us, body and mind; and their preservation is the ultimate rationale for our existence. They have come a long way, those replicators. Now they go by the name of genes, and we are their survival machines.

    Richard Dawkins, The Selfish Gene

  13. SaintStephen says

    Sheesh… got distracted from my original thought. I was just going to comment on the following coincidence:

    I walked into Borders yesterday, asked for any books by Carl Zimmer, and badda bing there it was — one paperback copy of Parasite Rex.

    God I love the anticipation of a good read!

    (Thanks to Jerry Coyne’s excellent thread on non-fiction book suggestions.)

  14. Carl Zimmer says

    Man, I either need new glasses or a new brain. Sorry for misreading your post, PZ.

  15. David Marjanović says

    Any alien biology introduced would probably just be food for indigenous microbes.

    Only possible in the extremely unlikely case that it uses the Earthly set of amnio acids.

  16. KOPD says

    Only possible in the extremely unlikely case that it uses the Earthly set of amnio acids.

    Just curious, because I am not a biologist, chemist, or anything of the sort. Does it have to be the exact same amino acids, or are there functionally equivalent ones that would suffice?