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viplex:
Hello
Does ONE global cycle in the simulation mean that in that time all of the robots ALL DNA will be executed once (independent of lenght)? Or is there a predefined amount of operations per robot in one global cycle?
The reason I'm asking this is: in my simulation my robs tend to reduce their DNA lenght. It's been 2,7 million global cycles now, and the average DNA lenght has gone down to half that of the original avg lenght.
thanks: Viktor

MacadamiaNuts:
It executes the whole DNA each cycle, as far as I know.

Shorter DNA means lower costs. Evo bots survive with a small amount of basic genes, so they often throw away everything else.

EricL:
Correct.  All DNA for every bot executes each cycle (subject to conditions coded in the DNA of course).

I never use DNA costs in my evo sims as I do not want any cost-based selective pressure towards smaller DNA.  Maca is exactly correct - such costs will serve to shrink DNA length over time all else being equal.

I should ponint out that even without any DNA costs, selection pressures still operate indirectly on DNA length.  A longer genome will mutate more often (mutations are proprotional to genome length).  Since most mutations are deleterious, having a longer genome means your functionality is more likely to degrade due to mutations.  Thus, selection tends to place slight downward pressure on genome length even without costs, all else being equal.  Of course, this gets balanced out by useful adaptations which by definition must utilize DNA.  So, if there is selection pressure to aquire new traits in your sim, the genome will grow in length all else being equal.  If not, it will shrink, to the point where the code for critical adaptations starts to be impacted.  Ignoring viruses, the average genome length in a sim without DNA costs will be the balance point of these two opposing forces.

viplex:
Thanks, I see the point now. Because I had set all DNA costs to 0, yet DNAs are still shrinking.
It occured to me.. would it happen like this in nature? I mean, if we suppose there is no selectional effect on DNA lenght, would the size of the Active DNA be shrinking due to similar mutations? Or we can never know...
To put it another way: is there such mutation in nature as lenght-dependent deletion or an equivalent one?

shvarz:
Actually, I don't think Eric is right here.  There is no pressure to keep genomes shorter.  

Say you have two genomes.  Their functional parts are the same, but one genome has a lot of junk DNA.  The second genome will get mutated more often, but these excess mutations will happen to the junk DNA and so will not affect fitness of the offspring.  Thus having a longer genome has no disadvantage.

That is actually what I see in my simulations - most genomes tend to get longer during evolution, acquiring junk. I once saw a situation where most mutations appeared to be deletions, but that was only once and I had some (very-very low) DNA costs.  I am actually suspecting that it was some kind of bug in a program, because I saw no other mutations but the deletions.  So that could have been just a fluke.  

Make sure you disable all DNA-associated costs, including all the costs on the left side of custom costs panel and the "DNA upkeep" cost on the right side of the panel.

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