Evolution from 'Pressure' and Time ?

[Widdekind]

According to Bray's book Wetware, whilst the sensory Receptor Complex, at the 'head' end of an E.coli cell, is highly structured and ordered, the Flagella molecular motor machines are distributed irregularly around the back and sides of the cell. In images shown, it looks like they 'anti-cluster', or tend to space apart, around the back of the cell. In any event, they are far less structured, than the sensory structure (which detects important chemical constituents, in the environment, through which the cell swims). And more, the propulsion system is functionally simple as well, with only two states -- swim full forward ('go'), and tumble to a stop.. Why, then, would, in the same cells, one structure seem 'advanced' (structured), whilst the other seem 'primitive' (unstructured, semi-structured) ? If all E.coli cells have been evolving for the same amount of time on earth (~4 Gyr), why would some structures be 'brady-telic' (slowly evolving, molecular fossils), whilst others 'tachy-telic' (fast evolving) ? Would not the following rubric account for the observations?

 

Number of Evolutionary Steps accumulated [math]\propto[/math] time x 'Evolutionary Pressure'

N ~ t x P

Seemingly, then, E.coli sensory systems have 'suffered' from higher evolutionary pressures, as compared to the still-simple Flagella propulsion system. Note, that the rate of evolution (N/t), is plausibly proportional to the 'pressure' applied (P).

 

Also, the book observes, that organisms with shorter generation life-cycle-times (like beetles & mice vs. men), have undergone more generations, than humans, and are therefore more evolved earth organisms. A higher potential evolutionary rate, amongst fast-reproducing bacteria, could explain, why bacteria 'beat everybody else to the punch', when it comes to evolving proteins, for digesting the cellulose in wood (say).

[CharonY]

From how I read you it appears that you may confuse organization with advancement and relate advancement with evolution.

 

This connection is not there. First of all, whether certain structures are more or less organized depend on their function. In order to sense gradients there has to be strict control on where the receptors are located, especially considering the small gradients they have sense (as most bacteria are not mace larger than a micron). It depends a lot on the type of sensors, though, as some, in contrast, have to be distributed more equally across the cell to work properly.

 

Thus the amount of organization is not a matter of advancement, but just a manifestation of their function. To be more precise, it is probably somewhat erroneous to consider the receptors more organized, both, motor and sensor proteins depend on specific localization within the cell, moreover motor proteins require a higher level of organization in terms of protein-protein interactions to work properly.

 

It is dangerous to overlay simple observations with simple narratives and build hypotheses from there, as biology tends to be at least several orders of magnitudes more complicated than on the first (and second) glance.