A SUMMARY AND COMMENTS ON "OBSERVED INSTANCES OF SPECIATION"
1. Introduction
[1.1] This article addresses the main points covered in the September 1, 1995 version of the article "Observed Instances of Speciation" ("OIOS") written by Joseph Boxhorn. Mr Boxhorn refers to himself, at the time of writing his article, as 'a student' who is obviously attending some academic institution (
see "OIOS" 3.0, para. 2).
[1.2] Please note that when the term 'non-specialist' is used in this article it refers to those people who have not studied biology. Likewise, the term 'specialist' refers to those academics who fall under the general title of 'biologists' (zoologists, botanists, etc).
[1.3] Although you the reader may be a specialist, I have tried to write in such a way so that even those with no knowledge of biology whatsoever can follow my analysis. So, if at times I may be stating the obvious (in your informed mind), I would ask for your patience and understanding.
[1.4] A reference number has been given for each paragraph (
e.g. [1.4]) in order to facilitate easier location of a specific text appearing in a particular paragraph, should this be necessary for discussion purposes. This numbering system should not be confused with that which is used for subject division in legal, business, and academic documents.
[1.5] Unless stated or indicated otherwise, the text of this article is completely my own work.
2. Purpose Of This Article[2.1] "OIOS" was brought to my attention via a thread in an online forum discussing evolution and 'creationism'. I had made this assertion:
[2.2] "
We have no tangible evidence that one species evolved into another"[2.3] Now, it has to be remembered - and I am being quite candid here - that beyond what I was taught at school (over 25 years ago), biology has never been a personal field of study. Therefore, my statement was based upon a non-specialist everyday common view of the word 'species'.
[2.4] Although my knowledge of biology is obviously limited, I hope that the reader will judge what is written here on its own merits, looking at any conclusions I have come to on the basis of logical reasoning alone. I have, of necessity, had to consult certain reference works in order to get a better understanding of terms used by biologists.
[2.5] This article is certainly
not a vehicle for expressing contempt for Mr Boxhorn's "OIOS". I found his article to be very well researched, well written, informative and indicative of a character who wishes to be sure of what he has been taught via the scientific community. Therefore his article, in my opinion, is worthy of respectful consideration.
3. Short Glossary Of Words[3.1] Presented below, is a small word list especially for the benefit of non-specialists. Each entry has been defined according to the relevant meaning found in the
Oxford English Reference Dictionary.
[3.2]
taxonomy - "The Science of classification, esp. of living and extinct organisms."
[3.3]
genus - "1.
Biol. A taxonomic grouping of organisms having common characteristics distinct from those of other genera. usu. containing several or many species and being one of a series constituting a taxonomic family. 2. A kind or class having common characteristics"
[3.4]
species - "1. A class of things having some common characteristics. 2.
Biol. A taxonomic rank below a genus, consisting of similar individuals capable of exchanging genes or interbreeding and denoted by a Latin binomial."
[3.5]
strain - "A breed or stock of animals, plants, etc."
[3.6]
speciation - "
Biol. The formation of new and distinct species in the course of evolution."
[3.7]
zoology - "The scientific study of animals, esp. with reference to their structure, physiology, classification, and distribution."
[3.8]
entomology - "The branch of zoology concerned with the study of insects."
[3.9]
morphology - "
Biol. The study of the forms of organisms."
[3.10]
phylogenesis - "The evolutionary development and diversification of groups of organisms or particular features of organisms."
[3.11]
obligately - "
Biol. That has to be as described (
obligate parasite)."
[3.12]
hypothesis - "1. A proposition made as a basis for reasoning, without the assumption of its truth. 2. A supposition made as a starting point for further investigation from known facts."
4. What Does 'Species' Mean?[4.1] Before considering the discussion on this subject as dealt with in "OIOS", I think it of importance for non-specialists to note this quote from "Encyclopaedia Of Animals" (
page 12, para. 1), edited by Dr Maurice Burton:
[4.2] "It was, however, left to a Swedish botanist, Karl von Linne (1707-1778), or Carolus Linnaeus as he preferred to be known, to take a revolutionary step. Linnaeus suggested that each species should be known by two names, a generic name and a specific name. Thus, the domestic dog is
Canis (name of genus)
familiaris (name of species)"
[4.3] After Mr Boxhorn's introduction, he takes up the subject of "Species Definitions" (
2.0). He says, "A discussion of speciation requires a definition of what constitutes a species". He reveals to the non-specialist that "This is a topic of considerable debate within the biological community". Of the "different species concept currently in use by biologists", he gives a resume of four, which he appears (to me) to consider of particular note. Of the four concepts, two especially stand out as being of particular relevance to how non-specialists and specialists often classify living things into 'species'.
[4.4] "
The Folk Concept of Species" (
2.1) is shown to be a mental grouping of animals and plants according to both their reproductive compatability and what they look like. It is used particularly among people who live "close to nature". FCS seems to me to be closer to the specialist term 'genus'. For instance, a horse and an ass not only have 'horse-like' features, but are able to mate and thus produce a 'horse-like' mule. Both the horse and the ass share a common genus (
Equus).
[4.5] "
The Biological Species Concept" (
2.2) is apparently "the theoretically
preeminent species definition" according to "OIOS". So it would seem that this concept (BSC) has wide acceptance amongst biologists, although Mr Boxhorn says, "The BSC is most strongly accepted among vertebrate zoologists and entomologists" (
2.2.1). Although there have been variations on the definition of BSC, I understand from "OIOS" that the current view of what constitutes a 'species' is a "reproductively isolated" group. This creates a more restrictive classification than FCS, as it is not based on whether one type of animal is
capable of reproducing with another, but whether it
naturally does so. When zoologists look at animals in their natural habitat, it becomes apparent by their behaviour whether or not they 'belong' to each as a group. That is why although a horse and an ass share the same genus according to the taxonomy of biologists, they have a different 'species' label, that is 'caballus' and 'asinus' respectively.
[4.6] "OIOS" informs us that there "is an abundance of asexual populations that this definition just doesn't apply to" (
2.2.2). It also states that "the BSC cannot be practically applied to delimit species". For practical reasons it may not be possible to test where the boundary between one 'species' and another may lie. Mr Boxhorn gives an interesting example concerning bluegill sunfish. He tells us that where he lives (Wisconsin) there are "16,000 lakes and ponds", and estimates that to test all possibilities of crossbreeding amongst varieties of bluegill sunfish would require a test sample of 60,000,000 of these fish!
[4.7] According to "OIOS" in practice even those who strongly support BSC use other means of identification such as "Phenetic (or Morphological) Species Concept" (
2.3), in which 'species' is defined as "the smallest groups that are consistently distinct by ordinary means". Even here, the author points out that "ordinary means" can mean different things to different biologists.
[4.8] Another way of defining 'species' is via "Phylogenetic Species Concepts" (
2.4), of which there are several. Each of these asserts that "classifications should reflect the best supported
hypothesis of the phylogeny of the organisms".
[4.9] Mr Boxhorn makes a most important observation with regard to the whole subject of observed instances of 'speciation': "What a biologist will consider as a speciation event is, in part, dependent on which species definition that biologist accepts" (
2.5) At this point in "OIOS" the author warns against using the BSC as a universal tool of measurement for delineating 'species'. Although, as he says the most reasonable concept to apply in many cases will be the BSC, in "many other cases some other definition will be more appropiate".
5. Mr Boxhorn Looks For Reports Of 'Speciation'[5.1] The first hurdle Mr Boxhorn had to negotiate was that of the lack of accessible collections of reports on 'speciation' events. Such a situation was indicative to him of a seeming lack of interest in biologists wanting to reference these events. He put this lack of interest down to the belief that "the biological community considers this [
i.e. about actual 'speciation' events] a settled issue" (
3.0).
[5.2] He also thought another reason to be that they had accepted the view that many 'speciation' events would take far too long to be observable in the lifetime of a human being, so a lot more theoretical 'speciation' events have been discussed than those that have actually been observed. Lastly, he notes the current trend towards discussion of 'How?' rather than 'Where?'
6. "OIOS" Notes On Valid 'Speciation'[6.1] "OIOS" remarks on the BSC's reasonably "unambigious" way of testing for 'species'. However, it is argued that physical isolation itself or selective breeding is not evidence of a 'species' boundary. Mr Boxhorn gives a very good example where human beings might selectively mate according to hair colour (
4.1.1). So, in that case the BSC could be used to define blondes, brunettes, and redheads as different 'species', even though they are all human beings. There may be a physical reason why a human being cannot mate with another human being, but that does not place a 'species' boundary between the two.
[6.2] Concerning "obligately asexual organisms", "OIOS" asserts that "it is not obvious how much change is necessary to claim that a population has speciated" (4.2). Of course, as "OIOS" points out, there are those 'species' which change shape within their lifetimes, but this does not make them a new 'species'. An example of this would be a caterpillar (i.e. it 'changes' into a butterfly).
7. Observed Instances Of 'Speciation'
[7.1] This article will deal only with observed 'speciation' examples given in "OIOS" to which BSC can be applied via the taxonomic scheme. It will not accept as 'evidence' those examples which have been 'hypothesized' or thought 'may' have been cases of 'speciation'. I will refer to these examples as 'observed BSC-definable'. Since I don't currently feel qualified to make comments in the field of genetics, I will not attempt to discuss those reports that deal explicitly with unusual chromosomal changes, nor any cases that fall into the category of "ambigious".
[7.2] "OIOS" gives four examples of observed BSC-definable 'speciation' in plants (5.1.1). In three of these cases each had a common genus - Primula, Trapopogonan, and Brassica.
[7.3] The strange case of the radish and cabbage is of particular interest as both have a different genus (Raphanus and Brassica, respectively). "Plants grown from the seeds were interfertile with each other. They were not interfertile with either parental species." These plants "had the foliage of a radish and the root of a cabbage". If this report is verifiable, then those who would define a 'species' by genus, would probably think that biologists might like to take another look at how they group vegetables. Certainly in this case there is obviously some compatibilty between the two groups. Nevertheless, I do find this example to be worthy of note.
[7.4] In the case of Woodsia abbeae (5.1) both 'parents' came from the same Woodsia genus. Likewise with the examples involving genus Stephanomeira and genus Zea.
[7.5] The cases reported involving fruit flies (5.3) all involve 'strains' of the same type of fly. So, any 'speciation' occurred within the same genus. This is true of examples relating to houseflies (5.4) and the Gall Former Fly (5.5).
[7.6] Examples involving flour beetles (5.6) and Lab Rat worms (5.7) involved the same type (different "strains"), as did the "parasite or symbiont" example (5.8).
8. Conclusion
[8.1] Its seems that the whole subject of 'speciation' is not as simple as it might at first seem. Given that their are differences of opinion over what constitutes a 'species', then 'speciation' events are open to interpretation based upon one's definition of 'species'. In the scientific community it appears that BSC as a means for determining 'species' plays a dominant role, however, there are other ways which are used in certain circumstances.
[8.2] The classification system in common use amongst biologists, is an academic framework in which to look at life forms, and like all man-made systems is not perfect. All the reports that I have commented on, bar one, have taken place within the same genus. My own definition of 'species' was at the time I made my online statement close to what biologists call a 'genus'. Such a demarkation of 'species' is based on actual procreational compatability. It is based upon a belief that there is a certain point at which cross-breeding meets a barrier which reads, "So far you may come, but no further".
[8.3] So to the online forum member who took issue with my statement concerning 'speciation', I would like to re-phrase it with the following additions:
[8.4]
I am not aware of any observable generation of any lifeform that would fall into the category of 'species' as I would mentally classify it. If I were pushed for a straight definition within the taxonomic system used by biologists, I would reply 'genus'. I am aware of a case where apparently a new 'genus' was produced from two different genera, but I reserve judgement on this until at least another example of this occurrence can be produced in such a manner that it can be examined (e.g. photographs, video stills) to my satisfaction. I hope you will respect my non-commital, for would you make a major change to a personal opinion on the basis of one third-hand piece of 'evidence', and one which you could not personally examine to your satisfaction?9. Important Update
[9.1] The same evening that I completed this article, I thought I would take a look at the genera for camels and llamas. I was amazed to find that these both have different genera (Camelus and Lama). However, both share the same 'family' name (next category above genus) of Camelidae. You may be wondering why I was interested in those two types of animals and why I was surprised by the different genera. Good point! Here is the reason why.
[9.2] Several months ago I was watching a documentary channel on cable television and saw with my own eyes a 'hybrid' produced from a camel and a llama. It appeared in good health. I was at first wide-eyed looking at this animal as if it had come from outer space!
[9.3] The first thing I wondered was how on earth this was possible from two different animal types. However, after the initial shock of seeing this hybrid, I realised that llamas and camels have a lot in common. If we take away the hump(s) and consider not the size, but the main characteristics of both animals it becomes apparent that there is a definite number of 'family' traits. Most noticeable to me were the unusual face (especially the eyes and mouth), the longish neck, and the legs.
[9.4] So, I looked up the entry on llamas in my animal encylopaedia and read that "of all the domestic animals it is the most suitable for the steep mountain paths and the hard ground and can go without food and water longer than any other". It also said that on "the march the animals go in single file, like camels", so it seemed they also share important biological and behavioural traits.
[9.5] These similarities made me think that in some cases genera as determined by biologists are not always as inclusive as perhaps they should be, and the 'family' name would be more akin to the idea of genus. Which is why adopting the biologists definitions, in my opinion, should not be used as an unbendable rule for determining types of groupings. Perhaps, then the "Folk Concept of Species" or the mental grouping of animals according to what they look like has a role to play here. My idea of 'species' is intrinsically based upon extremely distinct lifeforms, so a new 'species' to me would be the product of, say, a cat and a dog as they are significantly dissimilar. This means that convincing evidence of 'speciation', to me, would have to be on that level.
(Edited to include update. Original text not changed)
Edited by - NewWay on 7 August 2002 20:30:2
