So, picking up where post #60 left off.
Phylogenetic Species Concepts
There are several phylogenetic species definitions. All of them assert that classifications should reflect the best supported hypotheses of the phylogeny of the organisms.
One might think that to avoid claims of jargon, that one might define terms like "phylogeny." But that's okay, I'll go with what my computer dictionary says about phylogenesis:
> the evolutionary development and diversification of a species or group of organisms, or of a particular feature of an organism.
Again, this is being put forth as
a way to define what constitutes a species, within context of speciation, and broader context of what is evolution (or perhaps more precisely, evolutionary theory).
Baum (1992) describes two types of phylogenetic species concepts.
1. A species is the smallest cluster of organisms that possesses at least one diagnostic character. This character may be morphological, biochemical or molecular and must be fixed in reproductively cohesive units. It is important to realize that this reproductive continuity is not used in the same way as in the BSC. Phylogenetic species may be reproductive communities. Reproductively compatible individuals need not have the diagnostic character of a species. In this case, the individuals need not be conspecific.
Questions I have from the above are: "smallest cluster of organisms" isn't clear to me. I want to (try and) relate it to say 'cats' as a species known to me, and understand how 'smallest clusters of cats' helps within above context?
The second underlined part seems to go directly back to folk definition with language of "must be fixed in reproductively cohesive units." Reproductive being I would say key word. If not really key, could we remove that or alter that key word and still have that statement make sense?
I don't know if I understand what is meant by "reproductively compatible individuals need not have the diagnostic character of species." I double checked meaning of conspecific, which means "(of animals or plants) belonging to the same species." So, what this is telling me is that "phylogentic species" are essentially exceptions to the rule found in folk definition of species, or perhaps more accurately, not the sort of organisms that laypeople generally run into, unless they have utensils and/or (controlled) environments in which to study 'atypical' forms of species.
Which, to me, does somewhat beg the question of 'what is it we are defining again?" That question though is rhetorical. And question I really have at this point is whether my understanding noted in previous paragraph is in line with what is being put forth, or if there is something I am overlooking, based on what is being said (in the literature, up to this point)?
2. A species must be monophyletic and share one or more derived character. There are two meanings to monophyletic (de Queiroz and Donoghue 1988, Nelson 1989). The first defines a monophyletic group as all the descendants of a common ancestor and the ancestor. The second defines a monophyletic group as a group of organisms that are more closely related to each other than to any other organisms.
My dictionary went with the first definition of monophyletic. I'll accept that there are two, though 2nd one seems like elaboration of the first, really elaborating on what common means. And first strikes me as attribute of species (interpretive assumption) rather than definition (conveyance of exact meaning). The term attribute and definition are similar, though I just wish to note that we are 'suddenly' in domain of accepting 'descendants of a common ancestor' as definition of species. Which from folk definition, I can relate, but from something that goes beyond that, and say further backwards, I am not clear how we got to this point other than throwing out a term, and hoping it would stick, without much question.
I will note that this is one of first times the material has provided meaning of a term (in this case monophyletic) and I do find that to be helpful in terms of getting around jargon being used to try and convey understanding.
A recently offered hypothesis suggests that phylogenetic species concepts and the biological species concept may be highly, if not completely, incompatible.
Hmmm, that seems to be saying a lot. I was actually getting to point in all these definitions of thinking, this is perhaps good for consensus, where we don't necessarily have to choose one definition at the expense of the others. That we could allow for all to exist as helping us get at 'what really is a species.' But this statement of "completely incompatible" would appear to refute that logic.
"Parallel speciation" has been defined as the repeated independent evolution of the same reproductive isolating mechanism.
I understand, I think, what is being stated here, but not sure how it fits in with defining species. Again, seems like either attribute of say speciation or abstract way of presenting the data. It could also be implying (I think) that there isn't necessarily one, single common ancestor.
An example of this may occur when a species colonizes several new areas which are isolated from, but environmentally similar to, each other. Similar selective pressures in these environments result in parallel evolution among the traits that confer reproductive isolation. There is some experimental evidence that this might occur (Kilias, et al. 1980; Dodd 1989). The implication of this is that biological species (as defined by the BSC) may often be polyphyletic. If this occurs in nature, it could undermine the usefulness of phylogenetic species concepts.
Well, I'm going to say it does occur in nature if it occurs in human experimentation. I wish there were reasonable way around that assertion, but I would say it would be illogical to consider otherwise. Therefore, if it does occur in experiments, it is plausible that phylogenetic species concepts may not be useful.
I don't know if it's just me, but concept of 'parallel evolution' would seem to have significant impact on evolutionary theory. Though to be fair, I'm a bit early in the whole process of thoroughly understanding this stuff, so perhaps a) parallel evolution is accepted as 'standard' or b) has refutation that I am not aware of at this point.
Why This is Included
What is all of this doing in a discussion of observed instances of speciation?
Very good question. Though I think I have ideas why. But you go ahead.
What a biologist will consider as a speciation event is, in part, dependent on which species definition that biologist accepts.
Well that seems fairly critical, and in vein of subjective.
The biological species concept has been very successful as a theoretical model for explaining species differences among vertebrates and some groups of arthropods. This can lead us to glibly assert its universal applicability, despite its irrelevance to many groups. When we examine putative speciation events, we need to ask the question, which species definition is the most reasonable for this group of organisms? In many cases it will be the biological definition. In many other cases some other definition will be more appropriate.
So, we fit the definition to match the data? Interesting.
I would say if a Creationist asserted something (exactly) along lines of, "you evolutionists seem to ask the question which species definition is most reasonable depending on group of organism. And then depending on the cases you come across, you apply a different definition." That would be met with, "where did you get that from, we don't do that. We are about using consistent, empirically evidential data and not something that is subjective to the experimenter. You really need to check your facts before you speak about that which you simply do not understand."
Personally, folk definition still strikes me as most reasonable, unless one is concerned with studying organisms that no one reading this comes into contact with outside of labs, or outside of using special (extraordinary) utensils.
Next up: The Context of Reports of Observed Speciations
...in my next post on this tangent
