August 26, 2005 | David F. Coppedge

Molecular Motors Galore: How Did They Evolve?

Myosin is one of the cell’s little monorail motors that trucks cargo around the cell, pushes false feet into the surrounding environment, forces packages out the cell membrane, makes muscles move and wiggles hairlike cilia.  Scientists reporting in Nature1 found twice as many varieties of myosin (37) than were previously known (17) and decided to plug them into the evolutionary tree of life and figure out how they diversified throughout eukaryotic lineages.  Although they found many “synapomorphies” (apparent instances of “convergent evolution”), Richards and Cavalier-Smith think they reduced the diversity of myosins down to three ancestral types.  They wrote, “We conclude that the eukaryotic cenancestor (last common ancestor) had a cilium, mitochondria, pseudopodia, and myosins with three contrasting domain combinations and putative functions” (emphasis added in all quotes).  They did not elaborate, however, on how these mechanisms and functions arose in the hypothetical single-celled ancestor.  Margaret Titus, commenting on this paper in the same issue of Nature,2 said, “Analysis of their sequences in a wide range of organisms reveals an unexpected variety of domains, and provides insights into the nature of the earliest eukaryotes.”
    In another molecular-machine story, three scientists found that the cellular powerhouse motors named ATP synthase come in pairs.  Reporting in PNAS,3 they actually photographed pairs of the miniature machines – an incredible feat, considering they are only about 12 nanometers tall – and found them bridged together at 40° angles.  They suspect that this arrangement helps in the formation of cristae (curved membranes within the mitochondria) and stabilizes the little rotary engines as they generate ATP: “This complex is assumed to improve the efficiency of ATP synthesis by substrate-product channeling.”  The authors did not speculate on the evolution of the motors or of the larger structure that they call an “ATP synthasome complex.”  Additional proteins and enzymes, whose functions are as yet unknown, appear to take part in the operation.

1Thomas A. Richards and Thomas Cavalier-Smith, “Myosin domain evolution and the primary divergence of eukaryotes,” Nature 436, 1113-1118 (25 August 2005) | doi: 10.1038/nature03949
2Margaret A. Titus, “Evolution: A treasure trove of motors,” Nature 436, 1097-1099 (25 August 2005) | doi: 10.1038/4361097a.

Evolutionary theory is so useless.  The first two scientists ought to be humbly standing in awe of cellular wonders at the fringe of our ability to comprehend them, and all they wanted to do was speculate about how machines built themselves by chance.  Did Richards and Cavalier-Smith add any logical or observational support for evolution?  Assuredly not.  They merely assumed it from the start, then organized the observations into a presuppositional template.  Could they delineate the actual mutations and selective forces that morphed one form into another?  Could they tell how the original ancestral forms – already highly complex – emerged out of the primordial chemistry lab?  Did they even for a moment consider the possibility that apparent design might represent actual design?
    Each of these motors, and the functions they perform, are examples of what Michael Behe dubbed irreducibly complex machines.  Without myosin and the tracks on which they run already assembled and functioning, there would be no functional advantage on which natural selection could act.  But even if the motors and tracks emerged somehow, why would they persist if there were no jobs?  Like superhighways without towns and settlers, they would be like pork-barrel projects of dubious utility.  The entire cell is interdependent.  The cell as a unit has to have a high degree of minimum complexity in place before anything will work.  Such cavalier speculation as exhibited here is no more logical or useful than arranging the cars at an auto show into an evolutionary sequence and claiming they arose without designers.
    The article about ATP synthase, by contrast, did not walk into Storybook Land.  The team advanced our knowledge by using novel techniques to image the machines, and then offered a testable hypothesis about the purpose of the bridge structure.  Notice that this was an implicit intelligent-design assumption.  They assumed the bridging improved the efficiency of ATP synthesis by channeling the substrate into a coherent operation.  That can be tested, whereas evolutionary speculation about presumed ancestors cannot.  The paper also illustrated the common experience of biochemists that the closer we look at cellular structures, the more complex they become.  By extension, that means the harder it becomes to explain them by evolution, and the more we begin to see design on higher levels of organization and efficiency.  ATP synthase is wonderful enough, but to see it organized into an “ATP synthasome complex,” well – that’s awesome.

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Categories: Cell Biology

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