In the previous entry, I showed you how the eukaryotic cell plan is far more complex than the bacterial cell plan on multiple levels. We might add the existence of introns in protein-coding genes, and thus the need for a spliceosome, to the picture. And we’ll add more in the future. But for now, we have enough to acknowledge the existence of a mystery. Since bacteria teach us that life is possible without all this complexity, we can explore questions that remains in the collective blind spot of the non-teleologists – Why is the cell plan of the eukaryotic cell so needlessly complex?
We could try to explain this by invoking the large population sizes of bacteria and hypothesize that this difference is the consequence of purifying selection. After all, it is well known that natural selection streamlines bacteria for efficient replication. Yet while this may be part of the explanation, it leaves too many stones unturned. For example, does this mean that life originated from complex, rather than simple, beginnings, and natural selection has pruned away much of this ancient complexity? And how did the eukaryotic cell plan emerge in such a way as to escape the pruning shears of purifying selection? And why hasn’t purifying selection streamlined the machinery inside the yeast cell, an organism which exists as large populations?
To show you how deep this mystery goes, let’s focus on one example of needless complexity – the RNA polymerase.
It is well known that eukaryotic cells are more complex than prokaryotic cells. For example, while the typical eukaryotic cell is 10-100 micrometers in diameter, contains numerous membranous organelles, has an elaborate cytoskeleton, and reproduces through mitosis, the typical bacterial cell is only 0.2-2.0 micrometers in diameter, lacking organelles and cytoskeleton (or so it was thought), while reproducing through binary fission. Clearly, the cytological complexity of the eukaryotic cell is not needed in order to be alive.
Yet the theme of needless complexity repeats itself at increasingly smaller scales like a fractal image.
I’d like to go back to the discovery of a complex calcium signaling toolkit in the single-celled organism, Monosiga brevicollis. The researcher who discovered this toolkit in this protozoan, Xinjiang Ca, wisely raised the following question:
We conclude that an extensive Ca2+ signaling ‘toolkit’ exists in the unicellular choanoflagellates, preceding the origins of animals (Metazoa). The current hypothesis of Ca2+ signaling acquires new dimensions in light of this novel discovery. Why does such an apparently simple unicellular organism need a complex Ca2+ signaling machinery?
Yes, why does such an apparently simple unicellular organism need such complex Ca2+ signaling machinery? And it’s not just the calcium toolkit, as the same unicellular organism has a toolkit of tyrosine kinases that is “more elaborate and diverse than found in any multicellular organism.”
Because I think there may something very significant here, let me refer to this state as Needless Complexity (NC). This is not to say that this is functionless complexity, as I am willing to bet all this complexity plays a role in the lifecyle of Monosiga brevicollis. I suspect that out in the wild, these creatures live rather complex lives, and both the calcium and tyrosine kinase systems are involved in control and adaptation that are involved with the every day life of these creatures (for example, I would expect different systems may come into play in response to different environmental conditions and time of day).
This complexity is needless in the sense that it is not required for unicellular, eukaryotic life. That is, other species of protozoa are able to survive just fine without the elaborate calcium and kinase systems. Such complexity is therefore not needed for unicellular life, but will become needed for complex, metazoan life. NC is thus a feature that is recognized from a relativistic perspective.
I plan to expand in much more depth about Needless Complexity and its role as part of a mechanism for front-loading evolution.