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passive_fist comments on Design-space traps: mapping the utility-design trajectory space - Less Wrong

-2 Post author: joaolkf 10 November 2013 05:32PM

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Comment author: passive_fist 10 November 2013 07:00:34PM 7 points [-]

In evolutionary processes, fitness is a monotonic function, i.e., it will necessarily increase or be maintained, any decrease in fitness will always be selected against.

Not true; chance plays a huge role in natural selection. This isn't just a nitpick; chance serves the function that it serves to escape from local minima. Enzyme configurations, for instance, have often gone through less-fit intermediaries to arrive at more-fit solutions.

Comment author: ThrustVectoring 10 November 2013 07:21:33PM 3 points [-]

It's not quite monotonic, but the actual mechanism is much more difficult to visualize.

Instead of one point in design space, think of a cloud of points. This cloud makes a successor cloud. Each point in the cloud has weight in the successor cloud proportional to it's height, and makes points close to it in a random fashion.

There's a certain ability to hop over downward slopes, but it takes many generations to expect it (and the more severe and deep the downward slope, the more time it will take).

So, strictly monotonic local optima aren't necessary, but evolution tends to travel faster up steeper slopes.

Comment author: joaolkf 10 November 2013 08:03:04PM *  0 points [-]

Yes, both lines of thought did cross my mind once. But they are wrong. Mind that I'm talking about design-shaping processes, I'm not talking about all the design which are ultimately produced. That is, I'm not talking about which organisms are produced in each generation during the evolutionary process. Rather, I'm talking about which organisms are selected for and against by the process, I'm referring to the process in itself and what it does with designs over generations. And no matter how odd and random mutations a generation of organisms might have, no matter which less-fit intermediaries enzymes or whatnot, if they have less fitness they will be selected against. There's no mechanism which could, in a predictive manner, account for the fact those less-fit enzymes will almost certainly lead to more-fit enzymes. The less-fit will be selected against, and if they survive long enough to arrive at a more-fit design, then - and only then - they will be selected for. One thing is what evolution does to the design landscape from one generation to the next, another thing - very much related - is how that design landscape will look like.

Of course, a less-fit mutation might survive for a while, but it will always be continuously being selected against. Eventually, it might suddenly achieve a better fit design than all the previous, but it must do so against the odds of evolution. I think the lesson to bring home here is that we are talking about one specific design-shaping process, and there are many other - not predominant - processes at play when shaping the design of life on earth. Those are not evolutionary process.

Comment author: passive_fist 10 November 2013 08:50:48PM 2 points [-]

This is not consistent with what you said in the article (emphasis mine);

Evolutionary processes are limited by the topology of the fitness-design trajectory space, it can only go from design x to design y if there is at least one trajectory from x to y which is flat or ascendant, any trajectory momentarily descendent cannot be taken.

Comment author: joaolkf 10 November 2013 09:16:51PM *  0 points [-]

any trajectory momentarily descendent cannot be taken, (edited) by the evolutionary processes.

Thanks, I will make sure to make it clear in the post.

Comment author: ThrustVectoring 11 November 2013 04:35:53AM 1 point [-]

if they have less fitness they will be selected against.

I'm not disagreeing with you there. Being selected against is different than not being born in the first place.

Less fit directions have exactly as many direct children as more fit directions. The difference is that there are more grandchildren in more fit directions, and fewer in less fit directions. Depending on the parameters for how much variance there is from generation to generation, evolution can cross small (relative to mutations per generation) downward slopes in design space.

Let's have a ridiculously over-simplified example. There are four possible designs, AA, AB, BA, BB. AB and BA have value of .5, AA has value of 1, and BB has value of 2. Everyone starts at AA and has 1 child. 1% of children get moved from AA to AB or BA, from AB to either AA, or BB, from BA to either AA or BB. With 20k intial members, after one generation there's 200 members each of AB and BA. Those 200 members of AB have 100 children, one of which is BB. That lone member of BB has 2 children each generation until essentially everything is BB.

Ta-da, evolution managed to make it's way past a negative slope in design space and out of a local maxima.

I'm not saying that every local maxima can have some down-slope traversal, but that shallow enough moats can be crossed by random action. At this point, the now higher local maxima takes over.

If that's not enough, imagine that there are literally infinite starting members of a certain organism. After each generation, there will be an infinite number of each of every possible descendant. Even the less fit ones. It's trivial for evolution to get out of a local maxima with an infinite number of tries.

Comment author: joaolkf 12 November 2013 11:52:16PM 0 points [-]

Being selected against is different than not being born in the first place.

Agree. My point is that those designs with less fitness were not shaped by evolutionary process on that generation in which they decreased in fitness. It was a random process or whatnot. I'm not talking about all the designs that came to be, or to all beings who were or could have been born. I'm referring to what evolution does to design, and evolution does not make a design decrease in fitness, even though it may allow other process to do so. I think I'm not being clear here. Once we concentrate on things the evolutionary process actively does, in opposition to what may happen or what have happened, it should be straightforward that there are no decreases in fitness.