Unicellular to Multicellular Transition Doesn’t Require Much Retooling

Yet more reason to think the hypothesis of front-loading is both reasonable and plausible:

One of the most pivotal steps in evolution-the transition from unicellular to multicellular organisms-may not have required as much retooling as commonly believed, found a globe-spanning collaboration of scientists led by researchers at the Salk Institute for Biological Studies and the US Department of Energy’s Joint Genome Institute.

A comparison of the genomes of the multicellular algae Volvox carteri and its closest unicellular relative Chlamydomonas reinhardtii revealed that multicellular organisms may have been able to build their more complex molecular machinery largely from the same list of parts that was already available to their unicellular ancestors.

“If you think of proteins in terms of lego bricks Chlamydomonas already had a great lego set,” says James Umen, Ph.D., assistant professor in the Plant Molecular and Cellular Biology Laboratory at the Salk Institute. “Volvox didn’t have to buy a new one, and instead could experiment with what it had inherited from its ancestor.”

Altogether the findings, published in the journal Science, suggest that very limited protein-coding innovation occurred in the Volvox lineage. “We expected that there would be some major differences in genome size, number of genes, or gene families sizes between Volvox and Chlamydomonas,” says Umen. “Mostly that turned out not to be the case.”

“One of the most pivotal steps in evolution-the transition from unicellular to multicellular organisms-may not have required as much retooling as commonly believed.”

Allow me to quote myself from a few months ago:

So here is what we have.  Prokaryotic cells can be viewed as the highest expression of mutation and selection, for there is no better cellular candidate for a “self-replicator.”  Yet after billions of years, the prokaryotic cell plan has failed to achieve anything near the level of structural complexity as exhibited by the eukaryotic cell plan.  To reach such structural complexity, the cell design had to be radically retooled, partly through endosymbiotic union, a one-time event given the widely accepted monophyly of eukaryotes.  Once the eukaryotic cell design was established, prior to the radiation of all extant eukaryotes, the basic cell design was now capable of supporting the emergence of complex, metazoan life.  The evolution of metazoa did not require further extensive retooling of the eukaryotic cell plan, given that metazoan cells are so similar to protozoan cells; it was more like the natural outflow of the potential inherent in the eukaryotic cell plan.

8 responses to “Unicellular to Multicellular Transition Doesn’t Require Much Retooling

  1. Maybe you should copyright your blog.

  2. Why’d it take two billion years then?

  3. Probably because it didn’t:


    I’d say such multicellular existence probably spawned shortly after the origin of eukarya, as the eukaryotic cell plan is poised for this job (the above study supports my previous contention about this). So the transition to focus on is the one from mutlicellular existence to metazoan and plant-like complexity.

  4. Yep. Takes care of that objection in one easy copy and paste.

    But is the transition from prokarya to eukarya completely understood? Was it all endosymbiosis?

  5. Actually I meant unicellular to multicellular, not eukaryote to multicellular. Those archaea apparently had to cook for quite a while.

  6. But did multicellular life first appear with the first increase in oxygen?

  7. So Bilbo, you are wondering if the first two billion years were the “terraforming” stage?

  8. The geologic record shows that the step-wise rise of atmospheric oxygen at both ends of the Proterozoic gave rise to multicellularity and the Cambrian Explosion respectively.

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