|
gluadys -> RE: Ben Stein is right! Darwinists are tyrants. (5/16/2008 9:32:10 AM)
|
quote:
ORIGINAL: PromiseLander
It has been told to me that my understanding of evolution is wrong... Well, I've never claimed to be a scientist, and I was never taught evolution in school. Since I gave a "reader's digest" version of the Gospel in post #309 when I spoke of Propitiation, would someone be so kind as to give me the "reader's digest" version of what evolution is teaching nowadays? (about a paragraph please)
It takes more than a paragraph, but I will try to keep it short. This is very, very general and overlooks much detailed information. I also have left out all reference to supporting evidence. You will have to be curious enough to ask for that.
Species change genetically. Often this means nothing as genetic change can happen without making any difference to the species (genetic changes in non-coding DNA, synonymous changes). Sometimes, it does make a difference. When a member of a species is born with a genetic difference, it may show up as a morphological, physiological or behavioral difference as well. So, in every species we see variations in many traits.
Many variations are just interesting variations. They have no impact on how well organisms survive, how often they are able to reproduce, how many of their offspring survive. These differences may be regional, because it is most likely that parents and children will live in the same area, so in different regions of a species range, you will get different variations accumulating and generating different "ethnic" characteristics.
A minority of variations are influential in how well the organism survives and is able to reproduce. A variation that causes sterility, for example, means that even if the organism is healthy, it cannot reproduce and will pass no genetic information to the next generation. Most variations which impact survival do so negatively (harmful mutations). This is to be expected as most species get along very well as they are, so when change is not neutral (as in most cases) it is likely to be undesirable.
This means that most changes which impact survival lead to premature death (before reproduction or before the completion of the reproductive cycle) and/or inability to reproduce. So organisms with such variations contribute less to the next generation than those without them. The result is that harmful genetic change is restricted in scope, affecting a minority of the species in each generation. This is called purging natural selection.
Occasionally, the opposite occurs and a variation improves the ability of an organism to survive and reproduce. Organisms with this variation will tend to complete their reproductive cycle more often and not only have more offspring, but more offspring that survive through their own reproductive cycle. Over time, organisms that have this variation will come to form the majority of the species. This is called adaptive natural selection and when such a variation has become the expected norm for the species, the variation is said to be fixed in the species. The accumulation of such variations in a species over time contributes to changing the characteristics of the species. So species change over time.
Speciation is a special step. I mentioned regional variations. A species is spread out over a geographical range and through particular ecological niches. This means that different segments of the species reproduce in different areas and in somewhat different environments. Sometimes, different segments of the species become separated from each other so that they do not have any way of passing genetic information from one segment to the other. Sometimes this situation is temporary; sometimes it becomes permanent. When it becomes permanent, you now have two or more species where there used to be only one. Of course, these species will still be very similar to each other. But because they no longer mingle their genetic information, and because they will each continue to accumulate changes in their genetic information, they do become more different from each other as time goes on. In fact, diversity is encouraged, for diversity reduces the intensity of competition between similar species and allows for more organisms in each population to survive and thrive. So characteristics which at first naturally emerge as typical of a particular geographic or ecological range can become the basis of speciation--a permanent genetic separation between these two populations. As Darwin put it: varieties are incipient species. And of course, once a species is established, it is subject to the same flow of genetic change, variation, formation of regional varieties, etc. so it can also eventually break into two or more species.
The net result over time is a "family tree" of speciations, technically known as a phylogeny, which shows how species are related to one another. This is also called "common descent".
Finally, in addition to evidence, you will note that there are many things this outline does NOT say--things you may be very interested in knowing. Most of them are not spoken of because the theory of evolution is neutral on the topic. IOW the question really doesn't concern evolution, but lies in another field of science or outside science altogether.
Hope this helps. If anything is puzzling, or you wish to explore further, feel free to ask.
|
|
|
|