enduring through conservation and change


the role of DNA

The same DNA segment (gene) is used for the formation of an anther in a flower as for the antenna of a fly.  This segment provides a mechanism for the cell to generate daughter cells that join in a linear fashion to make a long flexible structure. 

Thus rather than thinking of DNA as a “code” that determines what will happen, I prefer the metaphor of DNA as a Lego set with which you can build many different things, or maybe better, a warehouse from where the operational dynamics of the cell can “order” the plans for whatever parts are about to be built by the cell, based on its current condition.  Of course RNA is also entailed in this process, there is for example what is called “messenger RNA” that you can think of as the courier sent to pick up the new plans from the warehouse. 

“The DNA plus all the other cellular components determine what epigenetic courses are possible to a an organism at the beginning of its life, but the actual epigenetic course that the organism follows in its particular life history arises in a systemic dynamics of recursive interaction with the medium in which it lives.”

This unit has grown into a lengthier unit than I intended, so I shall be brief here, and write informally rather than offering substantive references.  This page is not required for the continuity of the course.

a conservative megamolecule

The main thing about DNA is that it endures.  The self-replicating process is highly conservative, it has managed to accurately reproduce the molecule literally over millennia.  Of course as for other systems, it has been a mixture of conservation and change, so that some new additions are accepted along particular lineages, and some unused segments eventually discarded.

People have spoken about so called “junk DNA” that does not appear to be at all involved in anything that the cell does.  Perhaps these are protein-plans that are not required by a particular organism.  Perhaps they are obsolete sections that just keep on being conserved by the whole process.  I think of the metaphor of old computer code that can cumulate in a large complex program, and no one dares to remove as they are not sure exactly what it does or whether it is indeed “junk”.

download optional reading:

Reproduction and Heredity

pp 66- 68

Wikimedia Commons

discovery.com animal planet

diagram of Mimivirus, a girus

Wikimedia Commons

the selfish gene

The notion of the gene conserving itself is emphatically carried carried by the “selfish gene” metaphor that Dawkins proposed way back in 1976.  The problem is that “selfishness” connotes a kind of awareness that cannot pertain to a molecule.  However, the idea did serve to disabuse many people of the popular notion that the DNA was there for the purpose of conserving the organism. 

Molecules do not have emotions,
and they do not have purposes.

this or that?

“ ... the selfish-gene metaphor is ... tricky.  By injecting psychological terminology into a discussion of gene evolution the two levels that biologists work so hard to keep apart are slammed together.  Clouding of the distinction between genes and motivations has led to an exceptionally cynical view of human and animal behavior.” 

de Waal, Age of Empathy, p. 43

more is not more advanced

The largest DNA, that is the largest set of genes does not imply a more complex organism.  Polyploidy, the duplication of the whole set has happened in many organisms.  And recently so called “giruses” or viruses big enough to actually see, have been discovered in the oceans ... and they have a huge DNA component.  

What leads to complexity is not deterministic, it is always in the interplay between parts.  As Maturana says (Origin of Humanness, p. 185):