[EDIT] if the genetic mechanism responsible for bringing about evolution is random, and if the environmental favoritism of some heritable traits over others is non-purposeful (like in the example of the black peppered moth during the era of industrial revolution: see here), then one would expect to see some examples of evolution that results in emergence of species the members of which has lower fitness than those of its immediate ancestor species. What I mean by that is that the genetic material in the gametes of some members of some species undergo changes that results in the emergence of a NEW SPECIES the members of which has lower fitness, that can go live in a separate environment.
Are there such examples? if not then why?
I'm not asking here about examples of an offspring having lesser reproductive rate than its parents and yet that offspring belonging into the same species of the parents. Of course that is well known to occur, since many hereditary disorders clearly affects the reproductive rate and survival of the affected individuals. No I'm asking about the emergence of a NEW SPECIES the members of which has lower fitness than those of its immediate ancestor species. The reason why I've mentioned that members belonging to the new species go live in a separate place from that of its immediate ancestor species, is because if they live in the same place, then clearly members of the ancestor species having more fitness would overcome members of the newly emerging species, to result in their extinction by natural selection, that's why I'm asking if it is possible for members of the new species to travel to another environment where it can live, albeit being less fit than members of the ancestor species from which it emerged. I call that backward evolution, though the term is odd, to mean that the direction in that particular case of evolution was towards lesser fitness rather than toward increasing fitness of members of the newly evolved species.
Are there such examples in the history of Evolution.
I'm not asking if the mechanism of such a step in evolution is due to Natural Selection, I'm asking if that evolution step can occur? and if it had occurred? And what are possible mechanisms behind such a step?
With the founder effect, what I'm understanding is that migration is the cause of lessening in genetic variation of the original population, and that this can possibly further lead to emergency of a new less fit species.
What I'm asking about here is a little bit different, I'm asking if the emergence of the new species caused the emerging (less fit) population to migrate as to avoid competition with members of the more fit original species. And because of this separation in place both populations need not compete each other for available resources, since they live at distant places. In other words, if some mechanism caused the birth of some less fit individuals that belongs to a distinct species form its ancestor, and such that those less fit individuals migrated as to avoid competition with the more fit ancestors, and that by this migration they managed to survive and reproduce. So it is not that migration caused at the end the less fitness, as in the founder effect, No its the opposite, its the less fitness that caused the migration.
I hope the question became clear now.