Note: The information in italics is taken from:
http://www.talkorigins.org/faqs/faq-speciation.html#part5
Emphasis is placed by me, and my comments follow each segment.
The most compelling (to me) arguments made on this talkorigins page are listed here, with my comments. First a discussion of the definition of speciation reveals that the definition is more than malleable, it is flexible beyond being useful as a tautological tool. It is frequently tailored to be specific to the particular event. Moreover speciation is presumed (by many) fixed and settled feature of biology.
Definition of Speciation
“What a biologist will consider as a speciation event is, in part, dependent on which species definition that biologist accepts. 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.”
…
“The literature on observed speciations events is not well organized. I found only a few papers that had an observation of a speciation event as the author's main point (e.g. Weinberg, et al. 1992). In addition, I found only one review that was specifically on this topic (Callaghan 1987). This review cited only four examples of speciation events. Why is there such a seeming lack of interest in reporting observations of speciation events?
In my humble opinion, four things account for this lack of interest. First, it appears that the biological community considers this a settled question. Many researchers feel that there are already ample reports in the literature. Few of these folks have actually looked closely. To test this idea, I asked about two dozen graduate students and faculty members in the department where I'm a student whether there were examples where speciation had been observed in the literature. Everyone said that they were sure that there were. Next I asked them for citings or descriptions. Only eight of the people I talked to could give an example, only three could give more than one. But everyone was sure that there were papers in the literature”.
“Second, most biologists accept the idea that speciation takes a long time (relative to human life spans). Because of this we would not expect to see many speciation events actually occur. The literature has many more examples where a speciation event has been inferred from evidence than it has examples where the event is seen. This is what we would expect if speciation takes a long time.”
“Third, the literature contains many instances where a speciation event has been inferred. The number and quality of these cases may be evidence enough to convince most workers that speciation does occur.”
“Finally, most of the current interest in speciation concerns theoretical issues. Most biologists are convinced that speciation occurs. What they want to know is how it occurs. One recent book on speciation (Otte and Endler 1989) has few example of observed speciation, but a lot of discussion of theory and mechanisms.”“Most of the reports, especially the recent reports, can be found in papers that describe experimental tests of hypotheses related to speciation. Usually these experiments focus on questions related to mechanisms of speciation. Examples of these questions include:
Does speciation precede or follow adaptation to local ecological conditions?”
“Is speciation a by-product of genetic divergence among populations or does it occur
directly by natural selection through lower fitness of hybrids?”
“How quickly does speciation occur?”
“What roles do bottlenecks and genetic drift play in speciation?”
“Can speciation occur sympatrically (i.e. can two or more lineages diverge while they are intermingled in the same place) or must the populations be separated in space or time?”
“What roles do pleiotropy and genetic hitchhiking play in speciation?”
“It is important to note that a common theme running through these questions is that they all attempt to address the issue of how speciation occurs.”
“5.3.5 Sympatric Speciation in Drosophila melanogaster
In a series of papers (Rice 1985, Rice and Salt 1988 and Rice and Salt 1990) Rice and Salt presented experimental evidence for the possibility of sympatric speciation. They started from the premise that whenever organisms sort themselves into the environment first and then mate locally, individuals with the same habitat preferences will necessarily mate assortatively. They established a stock population of D. melanogaster with flies collected in an orchard near Davis, California. Pupae from the culture were placed into a habitat maze. Newly emerged flies had to negotiate the maze to find food. The maze simulated several environmental gradients simultaneously. The flies had to make three choices of which way to go. The first was between light and dark (phototaxis). The second was between up and down (geotaxis). The last was between the scent of acetaldehyde and the scent of ethanol (chemotaxis). This divided the flies among eight habitats. The flies were further divided by the time of day of emergence. In total the flies were divided among 24 spatio-temporal habitats.”
“They next cultured two strains of flies that had chosen opposite habitats. One strain emerged early, flew upward and was attracted to dark and acetaldehyde. The other emerged late, flew downward and was attracted to light and ethanol. Pupae from these two strains were placed together in the maze. They were allowed to mate at the food site and were collected. Eye color differences between the strains allowed Rice and Salt to distinguish between the two strains. A selective penalty was imposed on flies that switched habitats. Females that switched habitats were destroyed. None of their gametes passed into the next generation. Males that switched habitats received no penalty. After 25 generations of this mating tests showed reproductive isolation between the two strains. Habitat specialization was also produced.”
“They next repeated the experiment without the penalty against habitat switching. The result was the same -- reproductive isolation was produced. They argued that a switching penalty is not necessary to produce reproductive isolation. Their results, they stated, show the possibility of sympatric speciation.”
This initially compelling experiment fails to ask the initial question: why did the flies self-differentiate in the first place? Their eyes, at least the eyes of the progeny, were different colors indicating a prior differentiation of some sort. Perhaps they were not the same strain to start with. Keeping the logic of experiments true to the purpose is difficult, perhaps not really possible in the complexity of living things. In fairness, the report is not the original; keeping logic in reporting is also difficult. Other unanswered questions: control sample behavior; randomness of population sample selection for the experiment; purity of strain initially, and generations of purity (no recessive genetics), etc.
“5.7 Speciation in a Lab Rat Worm, Nereis acuminata
In 1964 five or six individuals of the polychaete worm, Nereis acuminata, were collected in Long Beach Harbor, California. These were allowed to grow into a population of thousands of individuals. Four pairs from this population were transferred to the Woods Hole Oceanographic Institute. For over 20 years these worms were used as test organisms in environmental toxicology. From 1986 to 1991 the Long Beach area was searched for populations of the worm. Two populations, P1 and P2, were found. Weinberg, et al. (1992) performed tests on these two populations and the Woods Hole population (WH) for both postmating and premating isolation. To test for postmating isolation, they looked at whether broods from crosses were successfully reared. The results below give the percentage of successful rearings for each group of crosses.
WH × WH - 75%
P1 × P1 - 95%
P2 × P2 - 80%
P1 × P2 - 77%
WH × P1 - 0%
WH × P2 - 0%
They also found statistically significant premating isolation between the WH population and the field populations. Finally, the Woods Hole population showed slightly different karyotypes from the field populations.”
It would be more compelling if the original population had been split as a control; this shows a presumption of valid control without actually being known to be valid control. It is still somewhat compelling, without being totally validatable. It should be falsifiable, with replication, but replication is not noted. So this is empirically incomplete.
“5.8 Speciation Through Cytoplasmic Incompatability Resulting from the Presence of a Parasite or Symbiont
In some species the presence of intracellular bacterial parasites (or symbionts) is associated with postmating isolation. This results from a cytoplasmic incompatability between gametes from strains that have the parasite (or symbiont) and stains that don't. An example of this is seen in the mosquito Culex pipiens (Yen and Barr 1971). Compared to within strain matings, matings between strains from different geographic regions may may have any of three results: These matings may produce a normal number of offspring, they may produce a reduced number of offspring or they may produce no offspring. Reciprocal crosses may give the same or different results. In an incompatible cross, the egg and sperm nuclei fail to unite during fertilization. The egg dies during embryogenesis. In some of these strains, Yen and Barr (1971) found substantial numbers of Rickettsia-like microbes in adults, eggs and embryos. Compatibility of mosquito strains seems to be correlated with the strain of the microbe present. Mosquitoes that carry different strains of the microbe exhibit cytoplasmic incompatibility; those that carry the same strain of microbe are interfertile.”
So. The mosquito can only breed to an uninfected mate. This relates to speciation how?? (question to self: what is “improper condensation of chromosomes”?)
“5.9.2 Morphological Changes in Bacteria
Shikano, et al. (1990) reported that an unidentified bacterium underwent a major morphological change when grown in the presence of a ciliate predator. This bacterium's normal morphology is a short (1.5 um) rod. After 8 - 10 weeks of growing with the predator it assumed the form of long (20 um) cells. These cells have no cross walls. Filaments of this type have also been produced under circumstances similar to Boraas' induction of multicellularity in Chlorella. Microscopic examination of these filaments is described in Gillott et al. (1993). Multicellularity has also been produced in unicellular bacterial by predation (Nakajima and Kurihara 1994). In this study, growth in the presence of protozoal grazers resulted in the production of chains of bacterial cells.”
OK, they produced the Great Dane of bacteria by eating up the small ones. Then they saw them to stick together, making them presumably harder to predate. Is this valid, replicable, nonreversible, etc and so on. If so what does it mean? Did any cells in the CONTROL population ever stick together? Get bigger? “Unidentified bacterium”? Why are such questions not even asked? Maybe in the actual reports, which I don't have.
