Stupid Evolution Quote of the Week: Cell Networks
A team of Chinese scientists analyzed protein interactions in yeast cells, and titled their paper in PNAS1 “The yeast cell-cycle network is robustly designed.” They “demonstrated that the cell-cycle network is extremely stable and robust for its function,” and “able to survive perturbations.” The beginning of the paper expresses the wonder the stimulated their research:
Despite the complex environment in and outside of the cell, various cellular functions are carried out reliably by the underlying biomolecular networks. How is the stability of a cell state achieved? How can a biological pathway take the cell from one state to another reliably? Evolution must have played a crucial role in the selection of the architectures of these networks for them to have such a remarkable property.
After analyzing the stable states, “big attractors” and checkpoints in the yeast cell cycle, the scientists remind us that this network is part of an even bigger marvel:
Note that the network we studied … is only a skeleton of a larger cell-cycle network with many “redundant” components and interactions…. Thus, we expect the complete network to be even more stable against perturbations.
… Furthermore, our results suggest that not only do biological states correspond to big fixed points but the biological pathways are also robust.
Functional robustness has been found in other biological networks, e.g., in the chemotaxis of E. coli (in the response to external stimuli) and in the gene network setting up the segment polarity in insects development (with respect to parameter changes) . It has also been found at the single molecular level, in the mutational and thermodynamic stability of proteins. In some sense, biological systems have to be robust to function in complex (and very noisy) environments.
And now to the climax. In the closing statement, after claiming several times that these networks are “robustly designed” (their term), they suggest that all this complexity, all this robustness, all this control and regulation is the product of time, chance and contingency. In fact, the very robustness might even help evolution make it better:
More robust could also mean more evolvable, and thus more likely to survive; a robust “module” is easier to be modified, adapted, added-on, and combined with others for new functions and new environments. Indeed, robustness may provide us with a handle to understand the profound driving force of evolution.
1Fangting Li, Tao Long, Ying Lu, Qi Ouyang, and Chao Tang, “The yeast cell-cycle network is robustly designed,” Proceedings of the National Academy of Sciences USA, 10.1073/pnas.0305937101, published online before print March 22, 2004.
Congratulations to the winners of this week’s Stupid Evolution Quote of the Week. Bravo. Now call the schizophrenia ward.
They may actually have a point. In the church, Christians are more likely to survive, and are easier to be modified, augmented, adapted and combined with others for new functions and new environments in the body of Christ if they are more “evolvable” (malleable) in God’s hand. Strength can be perfected in weakness, but only by intelligent design.