Monday, February 4, 2013

CH3: Accumulating Small Changes


      Evolution is a deterministic process. It consists of steps of small changes. Each change must be small so that it can happen by chance. A chance to step over a big change is much smaller than a chance to step over a small change. 


Genes and Evolution

“Genes in real life do two things. They influence development, and they get passed on to future generations.” 
     The role of genes in evolution are reproduction and development. Reproduction is a process of passing selected genes to the next generation. Development, on the other hand, is the process of genes to gradually develop into a body. Evolution is a repeated process of reproduction. 

“Genes only start to mean some- thing when they are translated, via protein synthesis, into growing- rules for a developing embryo.”

Mutation is Random, but Cumulative Change is not

     During reproduction, the genes could be mutated, i.e., it could be slightly different from the original genes.  Over time, the progeny can radically differ from the parent. Although the mutation process is random, but the cumulative change is not. 

     This is because of Darwinian selection. Only if the child differ from its parent in a given direction, will it able to pass on its genes to the next generation. For natural selection, that direction is towards tendency to survive.

Small Change, Sudden Change, and Evolution

      In nature, the chance of gene mutation is very small. An insect can mutate to another similar insect. But it would not be able to mutate to something like a frog. 
If big changes are possible, it can be said that an insect can evolve to anything with equal possibility. But since the space of all possible creatures are astronomical, the possibility of mutating to something better is infinitesimally small. A creature can mutate to something weaker and be extinct at the end. 

     But nature doesn’t work like that. It’s more like you are given a reward every time you mutate to the right direction. So the chance of mutating to something stronger is much higher. 

Single-Step v.s. Cumulative Selection 

     Selection can be single-step or cumulative. Single-step selection selects once and for all. Cumulative selection repeatedly feeds the result of a selection to another selection process.
For example, if we randomly select 40 letters at random to form a sentence of 40 letters. Each letter will appear in each of 40 positions in a sentence with probability 1/27 (26 letters and a space). So the probability of having the sentence exactly like “NATURAL SELECTION IS A BLIND WATCHMAKER” would be (1/27)40, which is very very small. Each of randomly chosen sentence is a single-step selection. The sentence is selected if matched, and is rejected, otherwise. The process repeats until, we got the exact match. Since the randomly chosen will be discarded and forgotten,it will take a very long long time to hit the target sentence “NATURAL SELECTION IS A BLIND WATCHMAKER”. 

     Cumulative selection is different. We begin by, again, choosing a random sentence. But in the next round , we generate new sentences by introducing random error or mutation to each letter. Then, we keep the sentence which is most similar to the target sentence. Then, we use mutation to create the next sentences in the next round. It takes only less than a hundred round to reach the target sentence. This is simply because, we did not throw away the result we had so far.

“Chance is a minor ingredient in the Darwinian recipe, but the most important ingredient is cumulative selection which is quintessentially nonrandom.”

     But to say that natural selection is like the above example would be misleading. In the above example, we have a target sentence “NATURAL SELECTION IS A BLIND WATCHMAKER”. Every generation tries to reach this target sentence. But life has no long-term goal. It has only a short-term goal, i.e., survival. 

     “The ‘watchmaker’ that is cumulative natural selection is blind to the future and has no long-term goal.”

Genetic Formula and Mathematics

     Now, suppose you run simulation for evolution with 3 genes, and you find the shape you like in the 30th generation. If you did not record the genes evolution, it would be virtually impossible to regenerate the result. Suppose the possible value of each gene is from 1 to 6. Then there are ((6)3)30 . It’s about 1.08 x 1070. The shape you like is one among all these possible shapes. If you forget to record how you get this shape, it is virtually impossible recreate the shape. You can recreate all possible shape. But you cannot pick one out of these possibilities. The space where the shape lies is just too astronomically vast. 

     Instead of searching through all possibilities, we need an intelligent search. This is like chess-playing software. The software uses efficient searching procedures to look for the winning moves, rather than computing all possible moves. 
If we’d like to find a certain shape that we like, we can’t look for all the shapes because there are way too many shapes. But we can redo the simulation and select what we like again. Then, we might be able to come across the shape that we saw earlier. They might not be the same, but they could be quite similar. 

     In nature, there are tens of thousands of genes. Each genes has a wide range of possible values. Therefore, the space of all possible creatures are astronomical. This space accommodates all creatures you can think of. Humans, whales, earth worms, dinosaurs --they are all in there. In theory, if you know the genetic pathway, you can recreate any creature. But again, the space is just too large. If we keep trying genetic codes at random, we could spend as much time as that since the beginning of this universe, and not being able to find the creature we like. 
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Book or Audiobooks?

Personally, I prefer audiobooks. It's fun, and I can listen when I'm doing something else. It also makes other activities (e.g., jogging) a lot more fun. For more detail about audiobooks, please read [this post].

There is one more reason that may encourage you to go for the audiobook version. You can get it now for FREE. Audible offers you a free trial for 14 days. Even if you get the book and cancel the subscription right away (so that you don't have to pay), you can keep the book. And, don't worry if you lost the audiobook file. Just log into audible.com. You can keep downloading the over and over again.
About the summary: It takes time to finish up a book. And, when you do, sometimes, you want to review what you learn from the book. If you do not make  notes as you read, you might have to go through the book once again. This can be time-consuming when you are dealing with a book. But you can still flip through the book and locate what you are looking for.

However, when the material is an audiobook, it is extremely hard to locate a specific part of content. Most likely you will have to listen to the entire audiobook once again.

This book summary will help solve the pain of having to go through the book all over again.

I am leaving out the details of the books. Most books have interesting examples and case studies, not included here. Reading the original book would be much more entertaining and enlightening. If you like the summary, you may want to get the original from the source below.

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