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Survival of the fittest

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Jez:
Here's a thought;

After a recent discussion following the post about Richard Dawkins and why bots devolve instead of evolve, plus a recent discussion about how the 'best bot' selection button works why not have an option to kill the worst bot? It seems to me, in my blissful cloud of ignorance, that enviromental pressures have a lot to do with the successful evolution of 'fit bots'.

While the intention is to add various enviromental pressures to the sims, these are perhaps a long term goal requiring a fair amount of work. Would it not be easier, certainly in the short term, even if we allowed for selection of what defined the 'worst bot' in the same way that there was talk of being able to define the parameters for the 'best bot', to allow for an arbitary cull of those misbegotten and unwanted offspring?

Perhaps a time or population controlled cull?

I realise that this might tread the icy thin waters of eugenics but it does, at this point in space, seem a reasonable way to emulate enviromental pressure without needing an pro-active or aggressive enviroment.

shvarz:
There is really no reason to kill "the worst bot", because if it is indeed the worst, then it will die off anyway.

In addition, even in theory there is no way to define which bot is the best or the worst.  The only truly objective way is to look at the "end of time" and see whose offsprings survived that far and whose did not.  But at that point all the bots are dead and there is no need to kill anyone

Numsgil:
A relatively simple way to define the "best" bot is the bot with the most loaded nrg in itself and its surviving offspring.  This is a relatively easy way to balance big berthas and cancerous bots.

But that doesn't help when you're selecting for "worst" bot.  Instead of selecting and culling a "worst" bot, I would have a disaster event, with two kinds of disasters:

1.  The first kills off any bot within some random location and radius.  This would simulate local disasters, such as a volcano.

2.  The second jacks up costs for several cycles (say, 100 cycles).

The idea is that the first kills off K-selected species while the second kills off r-selected species.

That sort of random death should provide the selective pressure to eliminate poor phenotypes.

Zinc Avenger:
I've often tried to think of ways of artificially (or perhaps semi-arbitrarily) increasing the fitness of a population of bots without editing dna, but this catastrophe-style method seems a bit harsh. Personally, I think bots have a hard enough time surviving as it is, and superior fitness is no guarantee of survival, so adding in new ways to kill them at this stage could be counter-productive, leading to selection of the lucky rather than the best. Oh, and yes, I do know that's how it works in real life!
 
My current leading idea, which is still in the early stages of consideration, is to scale each bot's point mutation rates by its unfitness (as fitness decreases, point mutation rates increase). Bots at the low-fitness end of the population get more point mutations, which will lead the bot to either break down altogether and die, or just maybe evolve that little step necessary to bump its fitness up.

Also under this scheme, the fittest bots will not point-mutate away from their current level of fitness. However, as the population's overall fitness increases the earlier high-fitness bots would find themselves dropping down the fitness tables for the population and start to mutate.

As I said, this idea hasn't been given my usual week of casual pondering before it gets its airing so please forgive any ragged edges!

Of course, the simplest method for artificially increasing the fitness would be to duplicate the current leading bot every 1000 cycles or so, but that could lead to bots losing their .repro commands when they become fit.

EricL:
I feel compelled to point out that in any evo sim where selection is in operation (zerobot sims where a first replcator has yet to emerge and take over don't count) ALL of the extant bots are likely to differ from each other by only a few base pairs at most with many of them being genticially identical.  They are all the same species.  The whole concept of determining "best" is rather silly in such populations - they are all 'best' in that they are all alive and relative to the vastly larger number of extinct ancestors, they all are fittest.   If you just want to select viable representitive individual, all you really want is a bot that didnt mutate that generation (since the probablity a mutation is deleterious is far greater than it being beneficial).  Other that that, one bot is really no more fitter than another - there just isn't enough genetic difference for the concept to be meaningful.  Fitness is a species-level (a genome-level) concept, not an individual-level concept and in a sim where there is essentially only a single genome (ignoring autotrofs) all bots are pretty much equally fit.

I have yet to see someone evolve a stable sim which supports multiple heterotopic species in proximity, where choosing one genome as 'fitter' than another might make some sense.  I'm using the term 'species' here in it's genetic sense, meaning two bots are of different species if they exhibit significant genetic distance in their genomes, even if they share a common ancestor.  Yes, in an asexually reproducing population, every bot is in some sense it's own species, but our sims are generally too small and too simple to support an acestrial line diverging from and yet coexisting with other extant lines.   Said another way, in every sim I've looked at where there isn't forced, physical isolation, ALL the bots in the sim share a common ancestor that is a surprisingly small number of generations in the past.  Note that I said 'stable' and 'in proximity'.  Yes you can get specieation when there is isolation, but that disappears when they are brought into proximity.  I've yet to see a true ecosystem where mutlple species in proximity have some sort of stable, niche-determined relationship which allows speciation in proximity to be stable (I.e. one is preditor, one is prey or perhaps one is herbavore and one is scavenger, etc.).   Until such time, the whole concept of fittest is suspect IMHO.

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