[DiscoverDave]

The recent post about mass-cell mutation by nanobots etc helped me to expand an idea about speciation when I misread "mass-cell" as "mast cell".

Originally, my idea involved only the natural selection of gametes within the parents' bodies due to external environmental factors as causing speciation, but it left a lot of unanswered questions about how we recognize other indivduals as belonging to the same species, especially for the purposes of reproduction.  This new idea involves changes in the immune system.

I think that two systems, the reproductive system, and the immune system, emerge from the same cell line and are also related functionally in that they both have “immortal cell lines”, that is, they continuously produce new cells: gametes and immune cells.  Furthermore, cooperation between the gametes and the immune system must exist so that the gametes do not suffer immune challenge (ie, attack by the immune system).   

Consider this scenario where a mutation in the immune system would cause a mutant offspring, and perhaps even speciation.  If the immune system mutates or changes due to environmental factors, it could alter the immune challenge that it presents to the gametes (specifically all those sperm), thereby causing a “natural selection” to occur within the parent’s body — most likely the male’s body with all its sperm.  This may allow some different gametes to survive, increasing their chance to fertilize an egg, and going on to produce a mutant offspring, perhaps a new species.  If environmental factors affect the immune system and/or the gametes in a population of individuals, then enough mutant offspring of the same new species may allow for enough genetic diversity so as to successfully give rise to a robust, new species. 

The “natural selection” of gametes within the multiple parent’s bodies due to environmental factors has been one of my ideas about producing enough genetic diversity in a new species for it to survive, but I hadn't added the immune system to the idea and, quite frankly, doing so expands it so as to make more sense, as I surmise next. 

Mutation to the immune system might also provide a new species with “self knowledge” that it is a new species.  Such mutations may allow the individual’s central nervous system to recognize others of its “kind” as kin — ie, as those with whom it should socialize and as potential reproductive mates.  For example, the first humans would have recognized other new humans as potential mates, and not the primates from which they came.  Otherwise, given the number of new species members to old species members, there would be a lot of fruitless inter-species miscegenation — not the kind of behavior that fosters successful, new species.

[_Stefan_]

If I have misunderstood you, please show me how.

Consider this scenario where a mutation in the immune system would cause a mutant offspring, and perhaps even speciation.  If the immune system mutates or changes due to environmental factors, it could alter the immune challenge that it presents to the gametes (specifically all those sperm), thereby causing a “natural selection” to occur within the parent’s body — most likely the male’s body with all its sperm.  This may allow some different gametes to survive, increasing their chance to fertilize an egg, and going on to produce a mutant offspring, perhaps a new species.  If environmental factors affect the immune system and/or the gametes in a population of individuals, then enough mutant offspring of the same new species may allow for enough genetic diversity so as to successfully give rise to a robust, new species. 

That is plausible.
 

Mutation to the immune system might also provide a new species with “self knowledge” that it is a new species.  Such mutations may allow the individual’s central nervous system to recognize others of its “kind” as kin — ie, as those with whom it should socialize and as potential reproductive mates.  For example, the first humans would have recognized other new humans as potential mates, and not the primates from which they came.  Otherwise, given the number of new species members to old species members, there would be a lot of fruitless inter-species miscegenation — not the kind of behavior that fosters successful, new species.

That is not plausible. The immune system and nervous system do not interact in that way, even genetically. The immune system's ability to distinguish "self" from "nonself" is not linked to the brain's recognition system. There is some evidence that individuals prefer mates who have immune system genes that are distinct from their own, but this has more to do with sexual selection theory (and my final paragraph) than to what you propose.

At every evolutionary "step" along the way from human-chimp common ancestor to humans, each individual would have been barely distinguishable from its parents or its offspring, and by extension, from the rest of the population sharing its gene pool.

The tendency to prefer to mate with a member of your own species is controlled by genes, i.e. it's instinctive. Obviously mate-choice genes are under strong selective pressure to cause correct mate choice even when the populations they are in are changing. This would be mediated through normal mutation and selection, i.e. random mutations leading to an increase in correct mate choice. Luckily they do not need to change dramatically from generation to generation, because of my previous mini paragraph. More intelligent social organisms would also be able to learn correct mate choice from other members of their species.