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One random mutation powers multicellular life?

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dividing choanoflagellate/Prehoda

The Darwinian begins to sound like an overconfident historian.

From ScienceDaily:

All it took was one mutation more than 600 million years ago. With that random act, a new protein function was born that helped our single-celled ancestor transition into an organized multicellular organism.

This release features Prehoda’s lab’s work on choranoflagellates (featured here and here already).

But then notice how it all gets qualified:

Prehoda and colleagues then used ancestral protein reconstruction, a technique devised at the UO by co-author Joseph W. Thornton, a biologist now at the University of Chicago. By using gene sequencing and computational methods to move backward in the evolutionary tree, researchers can see molecular changes and infer how proteins performed in the deep past. In the new research, gene sequences from more than 40 other organisms were put into play.

The team’s journey identified a mutation that was important for opening the door to organized multicellular animals that eventually no longer needed their tails.

They also found that the choanoflagellate flagellum is critical for organizing its multi-cellular colony, suggesting that this may have also been the case as our single-celled ancestor transitioned to a multi-cellular lifestyle.

Prehoda’s team suggests that the tail’s role became less important when the gene for an enzyme duplicated within cells, and a single mutation allowed one of the copies to help orient and arrange newly made cells. The protein domain that resulted from this mutation is found today in all animal genomes and their close unicellular relatives but absent in other life forms. More.

I (O’Leary for News) was suddenly reminded of something I’ve been hearing all my life: Boastful claims about having solved an enigma of history. Who faked up Piltdown Man? comes to mind. It happened only a century ago, during a time of massive, mostly preserved, documentation, and we still don’t know.

Now, there is nothing wrong in principle with being an overconfident historian, provided other historians are allowed a kick at the can.

The problem is that readers, absent that check and balance, get used to regarding evolution as a secular religion or philosophy. They think that they are closing in on The Facts because a scenario that sounds plausible to them has been provided.

Maybe. Maybe not.

That’s the problem with actually knowing a lot about evolution. It becomes a history, with all the baggage that history entails with respect to how firmly a conclusion can be drawn based on the evidence.

It was easier in the old days when the Darwin-in-the-schools lobby was just assumed in many quarters to be “right” in their every pronouncement. Knowing so much more now has changed all that.

See also: Conclusions: What the fossils told us in their own words

Here’s the abstract:

(Public access) To form and maintain organized tissues, multicellular organisms orient their mitotic spindles relative to neighboring cells. A molecular complex scaffolded by the GK protein-interaction domain (GKPID) mediates spindle orientation in diverse animal taxa by linking microtubule motor proteins to a marker protein on the cell cortex localized by external cues. Here we illuminate how this complex evolved and commandeered control of spindle orientation from a more ancient mechanism. The complex was assembled through a series of molecular exploitation events, one of which – the evolution of GKPID’s capacity to bind the cortical marker protein – can be recapitulated by reintroducing a single historical substitution into the reconstructed ancestral GKPID. This change revealed and repurposed an ancient molecular surface that previously had a radically different function. We show how the physical simplicity of this binding interface enabled the evolution of a new protein function now essential to the biological complexity of many animals. – Douglas P Anderson, Dustin S Whitney, Victor Hanson-Smith, Arielle Woznica, William Campodonico-Burnett, Brian F Volkman, Nicole King, Kenneth E Prehoda, Joseph W Thornton. Evolution of an ancient protein function involved in organized multicellularity in animals. eLife, 2016; 5 DOI: 10.7554/eLife.10147

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