Wrote a little Intro on Evolution

[Asimov]

So I'm sittin here kinda bored so I have decided to go into a bit more detail regarding Evolution and its evidences.

 

What is Evolution?

 

Evolution is a process. This process is defined by populations acquiring and passing on traits through the successive generations; a population being a group of organisms that live in a similar geographical location (The Spirit Bears of Vancouver Island) who share a crossflow of genetic information. More specifically, however, evolution is defined as the change in the frequency of alleles in a gene pool over time.

 

The Theory of Evolution posits three things:

 

1. The common descent of all organisms from a single ancestor or ancestral gene pool.

2. The manifestation of novel traits in a lineage.

3. The mechanisms that cause some traits to persist while others perish.

 

Part 1: Mechanisms for Evolution

 

There are a number of mechanisms that cause evolution, one of which most of you are familiar with. I will group them into two categories: Mechanisms that decrease variation and mechanisms that increase variation.

 

 

Decrease:

 

1. Natural Selection - The most commonly known mechanism of evolution. Through environmental pressure, populations are forced to adapt or become extinct. Traits that are undesirable (do not provide a reproductive advantage) will become weeded out of the population, and the traits that do provide a reproductive advantage will remain within the population. Of course natural selection can only occur through existing traits within the population, thus, while it would be more beneficial for all organisms to be able to survive in any environment at any given time it is not possible.

 

1a. Sexual Selection - Natural Selection that operates on factors that contribute to an organisms mating success. A peacock's tail or rippling muscled body coupled with citations of poetry and extroverted sensitivity are examples of this. It is basically traits that the opposite gender of a population would be more inclined to go for.

 

2. Genetic Drift - Since each successive generation is not simply a replica of the previous generation, but a sample of it (including errors in the genetic makeup), there will be traits that arise that do not contribute or degrade an organisms reproductive chances. This is (unlike Natural Selection) a completely random sampling (statistically) that is more apparent in smaller populations. These changes need not be adaptive but may become adaptive due to environmental pressures (known as exaptations).

 

Increase:

 

Mutations - The ultimate source of variation, mutations are errors in DNA. Sometimes letters in DNA (A,C,T,G) are changed to other letters, or entire lengths of DNA are inserted or taken away from the code. Others can be duplicated or inverted. Mutations are what create new information in the genetic code.

 

Most mutations are neutral (that is they do not give or take away an advantage), however there are some that are deleterious and some that are positive. An example of a deleterious mutation is the disease Down's Syndrome. An example of a positive mutation is the immunity to Malaria.

 

Recombination - Gene shuffling, such as when 2 humans reproduce, is the creation of new combinations of alleles in an organism. Since only half of a males genes and half of a females genes are contributed to the new offspring, the baby will contain traits from both people.

 

Gene Flow - When organisms migrate from a different geographical location and can interbreed with other similar organisms, this crossflow of genetic information can create new combinations and new information in the population. What would limit this would be the inability to breed with the migrated population (such as deer entering a new habitat where there are horses).

[Zach]

Nice and concise, Asimov. Good job.

[All Gods Fail]

Sigh...if only the creationists would read it.

[Dhampir]

Quite simple and to the point, inasfar as my understanding of the subject goes. But you might still need to dumb it down some more, 'cause even my limited grasp of the concept is still worlds beyond theirs.

[Samurai Tailor]

Few things.

 

1. Vague terms like "genetic information" are creationist bullseyes. Try not to introduce terms that are easily misunderstandable and/or might require a dissertation to explicate.

 

2. I think it is incorrect to say natural selection, sexual selection, and genetic drift are processes that strictly decrease variation.

 

The flip-side of the natural selection coin is that some individuals with certain mutations will succeed. Thus, on average, selection will encourage as much variation as it eliminates.

 

Genetic drift does not actually contribute to the fitness of an organism at all, so I cannot really imagine how it affects overall variation one way or the other.

 

3. Add something about the dependency of mutational fitness on environment. You mention the mutation that confers resistance to malaria, but the important part of it is that the environment provides the opportunity - via malaria-friendly conditions - for an otherwise problematic mutation to flourish.