Yet, you continually refer to individuals as the WAY the populations evolve. Irrelevant?
You keep making these claims to which I must agree or disagree, concerning individuals, and when I agree that it is so with SOME of them, you declare it is about populations.
Evolution is the way the offspring are different from their parents. If the changes trend in one particular direction, then the population, over many generations, evolves.
For example, giraffes evolved long necks. We can imagine jumping in a time machine and travelling back in time to see a population of
early giraffes that had much shorter necks. In that POPULATION, some of the INDIVIDUALS would have had necks slightly longer than average, and some of the INDIVIDUALS would have had necks that were slightly shorter than average. The INDIVIDUALS with the longer necks would have had an easier time getting food, since they could reach higher into the trees and thus get leaves that were beyond the reach of the individuals with shorter necks. So, the longer-necked individuals would have been more likely to survive because they had access to a food source that shorter necked individuals didn't have.
So, the INDIVIDUALS with the longer necks would have been able to produce more offspring than the shorter necked individuals, and the genes that produced a slightly longer than average neck would have spread throughout the POPULATION. So, if we jump in our time machine and travel ahead to see what this POPULATION is like after ten generations have passed, we'd see that the genes for the slightly longer than average neck are now in many if not all of the INDIVIDUALS. The POPULATION has EVOLVED to have a slightly longer neck than it did when we first saw them.
So individuals don't evolve themselves. If we took one of these early giraffes and could keep it alive forever, it would never get the longer neck. It's genes would never change. It could not evolve. Because evolution is how the INDIVIDUALS are different from their parents. But it's all the individuals in the population, because the genes spread through the population.
You have not shown it is valid for "the vast majority of cases."
There are two main factors that influence the traits that an organism has. The first is genetic and the second is environmental. If you have two members of a population that live together (say, two zebra in the same herd), then they are facing the same environmental factors and any difference between them is likely to be more genetic in nature than environmental.
So you can't discard my caveats simply because I am ignorant, if you want to convince me. It's ok with me if you deal with them later, but when you make generalizations, like to say that since the reproducible beneficially endowed genetics of an individual is more likely to survive and reproduce like offspring, you have only made assertions concerning how relatively often this happens.
Okay, but also try to see this from my point of view as well. If I was trying to explain to you how airplanes fly, I could tell you about how the curved surface of the wing produces lift, but if you start asking my why the wings have those little turned up bits at the very end, it's only going to introduce a lot of complicated aerodynamic theory which just isn't applicable to a "beginner's guide" sort of thing. I'm trying to show you the broad strokes here, and while your caveats may be valid, any explanation of them would require a more in-depth understanding. I'm trying to do the basic stuff first. Then you'll have the understanding required to look at the caveats.
As far as I know, beneficial variations CAN have an already existing within-the-species genetic basis, which, granted, is not to say that 'new' or even mutated variations can't be beneficial, but I have no reason to believe that new ones ever happen, nor any reason to believe that beneficial mutations are often reproducible.
New variations happen due to mutation, which is basically copying errors in the DNA when cells divide. If an individual has such a change, this mutation in their genetic sequence can be passed to offspring since the offspring gets half of its DNA from each parent.
For example, I have a daughter. She got half her DNA from me. If I had a mutation, and that mutation was in the half of her DNA that she got from me, then that mutation was passed to her, and she has it too.
Do you see the generalization there? Not saying you are wrong, just saying that what I understand to happen rarely, if beneficial, if mutated or new genetics, if reproducible, has not been shown to me valid as a generalization, such as you present.
I'm trying to introduce concepts here. It's difficult to understand how these concepts work within the framework of evolution before one understands ALL the concepts of evolution.
—or the non-survival. You make a positive out of what I see as mostly negative. But yes, it CAN happen in a positive way.
You are correct. When I said they can influence the survival, I meant "how well the individual survives," and that could indeed be a reduction in its chances of survival as you said.
I should think that positive traits, that are not already within-the-species —i.e. positive traits that are by 'new' genetics or by mutated genetics— aren't often readily reproducible. Sterility, or bred out by cross-breeding.
These traits aren't necessarily completely new traits. Often they are simply variations on what is already there. Completely new traits - like a horse being born with wings - just don't happen because the change in the DNA required for this kind of thing is absolutely huge, and when you make large changes, it's much more likely that you are going to end up with something that doesn't work.
Think of it this way:
If you are standing on the footpath (sidewalk in America), and you had to randomly move to a different part of the footpath, would you want to move a large distance or a small distance? If you randomly moved a large distance, say a mile, you could end up anywhere. Inside a building, on a road. You can't predict where. But if you randomly moved a smaller distance, say a foot, you are much more likely to stay on the path. And if you moved a very small amount, like an inch, you're almost certain to remain on the path.
Likewise, if there's a large change in the DNA when it gets copied into an offspring, then a large change is probably just going to end up with an unviable embryo. But a small change has a pretty decent chance of survival, because a small change is going to keep it close to something that works already (specifically, the parents).
"then it [might] pass that trait on to the offspring [if it produces offspring]." But I don't know that that individual will produce offspring; it has not been shown me. Are we still talking about within-the-species traits, or mutations?
Most species have a natural drive to produce offspring. Without reproduction, the genetic line dies out completely and there is no evolution.
And this stuff of "within-the-species traits" and "mutations" makes it sound like you think a mutation is something like that horse born with wings stuff. It's not. As I've said, most mutations are very small changes to what's already there, since larger changes tend to result in unviable embryos.
But it does make sense to me that beneficial traits are more easily spread than harmful traits that are by mutation. I also agree that individuals inheriting mostly harmful traits tend to die more easily than those with mostly beneficial traits. But I can't agree with the generalization that beneficial mutated traits will more likely produce offspring that will pass that gene down to successive generations, than those with harmful extant traits will reproduce. At least, not until it is shown me.
The simple answer is that the individuals with the beneficial traits will be likely to produce more offspring since they are probably going to live longer due precisely to the beneficial traits they have. A longer life means more breeding opportunities.
