Tuesday, 16 September 2014

Something Is Bugging Creationism.

Evolution doesn't read any rules and feels no obligation to conform to any norms, so we should expect the unexpected. If we didn't get the occasional surprise it would start to look just a little too predictable. If things were as the creationist loons and frauds like to claim, we would expect an intelligent, perfect designer, to at least show bit of consistency.

After all what perfection is there in randomness and how does no pattern at all look like design according to a plan? No doubt though the frauds will fall back on the traditional woo-woo excuse of ineffability and mystery and beyond human comprehension which renders their crackpot notion redundant as a predictive or explanatory tool and shows it up for the simple answer for simpletons that it was designed to be.

Take for example an unusual pattern of evolution leading to speciation published in Cell a few days ago. It involves a symbiotic complex in the cells of a species of cicada. Cicadas are large, sap-sucking insects characteristic of hot parts of the world. They seem to be almost characteristic of the Mediterranean coast - my children called them wizzers as they seem to sit in trees and on telegraph poles and wizz all day long. Cicadas, like several other species, depend on symbiotic bacteria to help with their digestion. The species in question has a 'normal' arrangement with two different bacteria living inside its cells - Sulcina and Hodgkinia. Their contribution is to make histidine and methionine which the cicadas need. However, in some cicadas Hodgkinia exists in two distinct forms which clearly split from the 'normal' type at some point in the evolution of this symbiotic complex.

  • Some cicadas have three obligate endosymbionts instead of two
  • This third endosymbiont resulted from a speciation event in an existing bacterium
  • The ancestor to this new endosymbiont had a highly reduced genome
  • This added complexity seems driven, in part, by nonadaptive evolution

Mutualisms that become evolutionarily stable give rise to organismal interdependencies. Some insects have developed intracellular associations with communities of bacteria, where the interdependencies are manifest in patterns of complementary gene loss and retention among members of the symbiosis. Here, using comparative genomics and microscopy, we show that a three-member symbiotic community has become a four-way assemblage through a novel bacterial lineage-splitting event. In some but not all cicada species of the genus Tettigades, the endosymbiont Candidatus Hodgkinia cicadicola has split into two new cytologically distinct but metabolically interdependent species. Although these new bacterial genomes are partitioned into discrete cell types, the intergenome patterns of gene loss and retention are almost perfectly complementary. These results defy easy classification: they show genomic patterns consistent with those observed after both speciation and whole-genome duplication. We suggest that our results highlight the potential power of nonadaptive forces in shaping organismal complexity.

Sympatric Speciation in a Bacterial Endosymbiont Results in Two Genomes with the Functionality of One
Van Leuven, James T. et al.; Cell , Volume 158 , Issue 6 , 1270 - 1280. DOI: http://dx.doi.org/10.1016/j.cell.2014.07.047

The surprise is that this arrangement seems to be non-adaptive i.e offering no particular advantage over the 'normal' form but what it has allowed is for the two forms of Hodgkinia to evolve on their own paths provided they remain synchronised so that one is complementary to the other. This is only possible in the special conditions where all four members of this symbiotic complex are inter-dependent. It seems to be an example of an accidental duplication allowing one of the pair to then lose genes provided the other member retained it, so we have ended up with two forms being almost mirror images of one another.

In many ways this replicates the situation of accidental gene duplication within a cell nucleus, freeing one copy to mutate and evolve without harming the organism, but, as with parasites, the tendency with symbionts is not to increase complexity but to reduce it, so each form of Hodgkinia has become less complex as a result, losing between them a total of 64 genes from the original 137. The difference here is that each form of Hodgkinia occupies its own cell type within the cicada but they are all so mutually interdependent that they behave more like a single species with a distributed genome.

A fascinating example of non-adaptive evolution by genetic drift in the highly specialised, special environment of an advanced symbiotic complex and totally incomprehensible as the product of an intelligent designer of course. Why do the same thing two different ways, even using the same organism to do it in, when there is no detectable benefit from one way over the other?

It's beginning to look more and more like this notional intelligent designer's plan is exactly like the plan of someone who hasn't got a plan.

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1 comment :

  1. Your blog's final sentence - "It's beginning to look more and more like this notional intelligent designer's plan is exactly like the plan of someone who hasn't got a plan" - is a big understatement. Rosa. Don't forget that this illusory Intelligent Designer also must be irresolute and insecure, since He deliberately, or (even worse) accidentally, exterminated 99.99 percent of all the species He created. For more details, see: https://www.youtube.com/watch?v=7pL5vzIMAhs&list=PLED25F943F8D6081C . The video's title is: Does the Universe Have a Purpose? feat. Neil deGrasse Tyson.


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