Tuesday, March 26, 2013

CH8: Explosions and Spirals

Feedback System and explosion

A feedback system is a system where the output is fed back to the system as an input. There are two main types of feedback systems: Negative and positive feedback system. In a negative feedback system, the amount of feedback input decreases as the output increases. It is very useful to control the system at an optimal level. 

On the other hand, the feedback input in a positive feedback system increases as the output increases. The input accumulates even with a small increase in output. It is this accumulation which will lead to explosion in the end.

Positive Feedback and Sexual Selection: Female’s whim v.s. Male’s Ornament


Constructive Evolution

There are two processes contributing to constructive evolution: Coadapted genotype and arm races. Coadapted genotype or coevolution refer to the fact that genes adapt cooperatively rather than individually. Rather, they evolve as a team. Arm races happen when several species compete for their existence.

Coadapted Genotype

“In natural selection, genes are always selected for their capacity to flourish in the environment in which they find themselves.”
Environment refers to the surrounding condition.   Animals which can deal with predators and climate better will live longer. Similarly, genes which deal with the environment better tend not be eliminated by natural selection.
So, what does ‘environment’ mean to genes? A gene is usually surrounded by genes. So, genes which deal with other genes better will be more likely to reproduce.
So genes do not evolve individually. They evolve as a team. Once a team has advantage edge, it is hard for other teams to break in, even if the other teams are more efficient.

Arm Races


Enemy is defined as anything that makes life harder. Lions are  enemies of zebras. Zebras are also enemies on lions. If there was no zebras, lions would starve to death.


Animal can adapt to climate (e.g., having thick hair in cold places) in a few generations. If climate is the only factor which causes evolution, animal will stop evolving once it fully adapts to the climate. Not until the climate changes, will the animals start to adapt again. But, since the climate changes slowly but constantly, animals have never stop evolving.

Dynamic Environment

Climate is not the only cause for animal evolution.  The concept of predator and prey also triggers evolution. Predators need to hunts better, while preys need to avoid being hunted better. This is the concept of arm races. Arm races prevent predators and preys to stop evolving.
Climate and arm race affect evolution differently. Climate is a static environment. It does not adaptively change itself. In arm races, animals are the active environment. Since animals constantly go through cumulative selection, the environment for arm race adaptively changes itself. Predators have to be better. Preys have to be better. Overall, arm race makes life forms be better over time.
“One side gets a little better because the other side has. And vice versa.”

Types of Arm Races

There are two different types of arm races: Symmetric and asymmetric arm races.

  • Symmetric arm race refers to when competing units strive for the same thing, e.g., trees compete for sunlight.
  • Asymmetric arm races, on the other hand, refers to when competing units strive for different (and usually opposite) things. For example, lions strive to hunts zebras, while zebras strive to avoid being hunted. This type of arm race is very powerful in evolution, since it forces both competing units to constantly adapt itself. 

Economics Stops Arm Races

If arm races help animals evolve constantly, we should have seen cheetahs or gazelles which can run at the speed of sound already. We have not. So, what does stop cheetahs or gazelles to evolve to be better runners?
It’s the Economics. If cheetahs had bigger muscles to let it run faster, the muscles would consume more energy. Cheetahs would not have enough energy to do other activities (e.g., producing milk for their youngs). So, the evolution stops when the benefit of arm races becomes uneconomical.
One note is that most of the time preys will develop more ability for arm races. This is because preys need to run for their life, while predators just have to run for their dinner.
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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