I posted this in response to Carico, but since it seems to have been wasted there, and I think it probably serves as a good introduction to evolution for anyone, I'm posting it here, in a new thread. I've tried to simplify it as much as possible (not hard, since I only know the basics myself), though any errors within I would love to be pointed out so I may correct them.
Theory of evolution (not to be confused with the observed fact that evolution takes place) is the theory that explains the current diversity of life on Earth as a result of populations becoming adapted to their particular environment.
In every cell, we have DNA stored in the nucleus. This DNA is identical for every cell in our body. It is this that determines how the cell behaves, grows and reproduces, through chemical reactions.
Every time a cell duplicates - as almost all cells do - there is a chance of an error in the copying of the DNA. This is called a mutation, and has been observed. However, a single cell with a mutation is no good for organisms with lots of cells. It won't affect the whole organism. This is why doctors don't wait for cancer cells to 'mutate'. Because mutations only occur for individual cells. The odds of every cancer cell 'suddenly' mutating to be non-cancerous are astronomical. The odds of one doing it? Probably not so unlikely. But one cancer cell reverting to normal will not help.
The important mutations are the ones that take place when the egg and sperm cells are created. These carry the DNA for the offspring. So if there is a mutation within either of those, the whole organism that the egg or sperm eventually produces will have that same mutation.
Mutations are usually small. Very often, they are harmful or even fatal. Many times, they are neutral. But sometimes, rarely, they are beneficial to survival in that particular environment. Note that the environment includes everything from the temperature and average rainfall to the type of predators in the area.
Organisms with beneficial mutations are more likely to be successful at reproducing - and thus passing on their DNA. Their offspring will carry those beneficial mutations.
Over time, the entire breeding population in that environment will aquire those beneficial mutations - simply because those with the mutation are better at producing offspring.
These changes are cumulative. Every beneficial mutation is kept, every harmful mutation is lost - simply because organisms with harmful mutations don't breed as well, while organisms with beneficial mutations breed better. Each new, beneficial mutation is added onto the last one. The changes become more and more pronounced.
In different environments, different mutations are beneficial or harmful. This means that in different environments, populations will adapt differently. Over time, two populations in different environments which were once of the same species become so different that they can no longer interbreed - thus, seperate species.
Over longer periods of time, different species can become so adapted to their environment they no longer even look anything alike. Sometimes the differences in apperance are not so great.
That is a very simplified explanation of theory of evolution.
Theory of evolution (not to be confused with the observed fact that evolution takes place) is the theory that explains the current diversity of life on Earth as a result of populations becoming adapted to their particular environment.
In every cell, we have DNA stored in the nucleus. This DNA is identical for every cell in our body. It is this that determines how the cell behaves, grows and reproduces, through chemical reactions.
Every time a cell duplicates - as almost all cells do - there is a chance of an error in the copying of the DNA. This is called a mutation, and has been observed. However, a single cell with a mutation is no good for organisms with lots of cells. It won't affect the whole organism. This is why doctors don't wait for cancer cells to 'mutate'. Because mutations only occur for individual cells. The odds of every cancer cell 'suddenly' mutating to be non-cancerous are astronomical. The odds of one doing it? Probably not so unlikely. But one cancer cell reverting to normal will not help.
The important mutations are the ones that take place when the egg and sperm cells are created. These carry the DNA for the offspring. So if there is a mutation within either of those, the whole organism that the egg or sperm eventually produces will have that same mutation.
Mutations are usually small. Very often, they are harmful or even fatal. Many times, they are neutral. But sometimes, rarely, they are beneficial to survival in that particular environment. Note that the environment includes everything from the temperature and average rainfall to the type of predators in the area.
Organisms with beneficial mutations are more likely to be successful at reproducing - and thus passing on their DNA. Their offspring will carry those beneficial mutations.
Over time, the entire breeding population in that environment will aquire those beneficial mutations - simply because those with the mutation are better at producing offspring.
These changes are cumulative. Every beneficial mutation is kept, every harmful mutation is lost - simply because organisms with harmful mutations don't breed as well, while organisms with beneficial mutations breed better. Each new, beneficial mutation is added onto the last one. The changes become more and more pronounced.
In different environments, different mutations are beneficial or harmful. This means that in different environments, populations will adapt differently. Over time, two populations in different environments which were once of the same species become so different that they can no longer interbreed - thus, seperate species.
Over longer periods of time, different species can become so adapted to their environment they no longer even look anything alike. Sometimes the differences in apperance are not so great.
That is a very simplified explanation of theory of evolution.
