I just want to understand the concept of natural selection and its relation to evolution.
Evolution by natural selection occurs when we have hereditary trait(s) that causes an effect on reproduction rate of a population, either towards the positive, and thus deemed as beneficial or towards the negative and thus labeled as harmful.
Evolution by natural selection would result in keeping the beneficial trait(s), and wiping out the harmful ones.
The idea according to Darwin is that the slightest harmful effect a hereditary trait(s) would bring to a population then with time it would result in extinction of the population with that trait(s). [On the origin of Species, p.78, chapter: natural selection: "On the other hand we may feel sure that any variation in the least degree injurious would be rigidly destroyed"].
Therefore natural selection could be viewed to result ultimately in washing out of injurious traits, and only promoting beneficial traits. So natural selection can be the cause of extinction of some genotypes, and ultimately of some species.
In this sense natural selection can be considered as a creative natural tool, like a rubber wiping bad intermediate solutions, and only keeping the correct steps, thereby facilitating reaching into a solution.
Now suppose that we have a population of living subjects with varying heritable traits on an Island, and those had equal fitness over a very long period of time, so they were pretty much adaptive to their environment. Now suppose a volcano erupted or a big comet stroked that island that ended all life in it. Lets suppose that the genotypes of that population is not present outside of that Island. So these genotypes became extinct.
Here this event doesn't have the same functional genre that natural selection had, it actually didn't act in a differential manner promoting those genotypes with better fitness and wiping out those with lower fitness. No it actually was NOT fitness dependent at all, it simply squashed all life forms without regards to whatever feature was brought up by the different genotypes, all were simply extinguished.
Now can we label this event of indiscriminative extinction to be the work of natural selection also? Or we just label it as inadvertent environmental factor?
If the latter, then are those inadvertent environmental factors part of the mechanism for evolution?
Let me give another example:
The beetles stochastic example
Suppose we have a population of brown and green beetles, now suppose that we divide the place they live in into two territories A,B, now suppose that the movement of beetles across those territories is random, so at some moment of time all brown beetles happen to be in territory A, other times they have different distribution, and as said the movement pattern is totally random, i.e. there is no significant difference in the pattern of movement of both genotypes of beetles across territory A and B. Now suppose by the act of randomness a moment came where all brown beetles were located at Territory A, while some of the green beetles were in territory A and others in territory B, and suddenly came a big comet and hit territory A at that time that caused all the brown beetles to die, and also caused all green beetles on territory A also to die, but since territory B was not hit, the green beetles in B remained a life.
Now a moment of evolution did occur, since a change in the heritable characteristics of the beetle population did occur. But that change was merely accidental, there was no role attributable to fitness of the green beetles that resulted in their survival, it was a mere random event that caused all of the brown beetles to die. In some sense it's a kind of a stochastic environmental factor that caused that extinction. Fitness of the green beetles didn't have any role in that case of differential survival.
This can be called selection, it is environmental kind of selection, BUT it is NOT the outcome of differential fitness of the genotypes in that environment.
Now this moment in evolution is it described as an event of evolution by natural selection?
More broadly speaking, is it the case that any point of change in the heritable characteristics of a population (i.e. evolution) that is merely due to an environmental factor [like the above example], would qualify as a case of evolution by natural selection? or only those points where the resultant change is attributable to fitness differential that is genotype determined?