Posted on 09/20/2007 7:51:35 AM PDT by Alter Kaker
The discovery of four fossil skeletons of early human ancestors in Georgia, the former Soviet republic, has given scientists a revealing glimpse of a species in transition, primitive in its skull and upper body but with more advanced spines and lower limbs for greater mobility.
The findings, being reported today in the journal Nature, are considered a significant step toward understanding who were some of the first ancestors to migrate out of Africa some 1.8 million years ago. They may also yield insights into the first members of the human genus, Homo.
Until now, scientists had found only the skulls of small-brain individuals at the Georgian site of Dmanisi. They said the new evidence apparently showed the anatomical capability of this extinct population for long-distance migrations.
“We still don’t know exactly what we have got here,” David O. Lordkipanidze, the excavation leader, said Monday in an interview on a visit to New York. “We’re only beginning to describe the nature of the early Dmanisi population.”
Other paleoanthropologists said the discovery could lead to breakthroughs in the critical evolutionary period in which some members of Australopithecus, the genus made famous by the Lucy skeleton, made the transition to Homo. The step may have been taken more than two million years ago.
“The Australopithecus-Homo transition has always been murky,” said Daniel E. Lieberman, a paleoanthropologist at Harvard University. “The new discoveries further highlight the transitional and variable nature of early Homo.”
The international team led by Dr. Lordkipanidze, director of the Georgian National Museum in Tbilisi, found several skulls and stone tools at Dmanisi in the 1990s. They were dated to 1.77 million years ago and resembled Homo erectus, the immediate predecessor of Homo sapiens. The fossils were tentatively assigned to the erectus species.
(Excerpt) Read more at nytimes.com ...
You can make the same claim a thousand times a day if you'd like, but it's still not true.
Creationists seem to inhabit a strange world full shibboleths and fake facts and mythologies.
And, of course, the fossil record shows species appearing suddenly and fully formed, matching the Creationist model and completely refuting Darwin.
Except in the many thousands of instances in which you choose to ignore the fossil record. See the article, above, for a timely example.
It’s amazing how Creationists will take any finds and proclaim them garbage with regard to advacing our knowledge.
I for one appreciate the news on these finds, and as long as they temper the claims with the items you specifically cite, then it’s A-OK with me.
Creationists keep claiming that fossils are either fully ape or fully human, but they can't agree on which are which!
Maybe that's because they arguing from religious belief, accompanied by a serious lack of training in science, eh?
The link below has a good graphic showing just how certain creationists classify various fossil specimens. One quote from the article:
Creationists, on the other hand, assert that apes and humans are separated by a wide gap. If this is true, deciding on which side of that gap individual fossils lie should be trivially easy. Clearly, that is not the case.Comparison of all skulls.
Personal letter from Dr. Colin Patterson, Senior Paleontologist at the British Museum of Natural History in London, to L. Sunderland
"A five million year old piece of bone that was thought to be the collarbone of a human like creature is actually part of a dolphin rib...The problem with a lot of anthropologists is that they want so much to find a hominid that any scrap of bone becomes a hominid bone."
Dr. Tim White (anthropologist, University of California, Berkeley), as quoted by Ian Anderson in New Scientist, April 28, 1983, p. 199
"In fact, evolution became in a sense a scientific religion; almost all scientists have accepted it and many are prepared to 'bend' their observations to fit in with it."
H. S. Lipson, FRS (Professor of Physics, Univ. of Manchester, UK), 'A physicist looks at evolution', Physics Bulletin, vol. 31, 1980, p. 138
One thing that a fossil record cannot do, and could never do,
is show that “this fossil is an animal descended from this other one”. The medium is simply inadequate to show that.
Now, if someone could show “speciation” happening TODAY, then we might pay attention.
oh, cool...transitional fossil evidence...they finally dug up one...they think.
It's strange how creationists attempt to argue fact with lists of obscure quotations, as if scientists secretly believe that our theories are all hogwash, and will only admit it in the deepest darkest recesses of their cabalistic institutions.
It is funny that you would post this picture. When I saw the word “Georgia” before “former Soviet Union.” I immediately thought of the former POTUS from Georgia USA.
LOL! Yeah, I guess the creationist "model" is pretty airtight scientifically. I mean, who can argue with "God did it" as the answer to any scientific inquiry.
Actually, they've dug up thousands of transitional fossils, but this is an unusually clutch one, as we know comparitively little about the boundary between Australopithecus and Homo.
That's easy. Here is evidence of speciation, with all transitionals still living!
Ring species provide unusual and valuable situations in which we can observe two species and the intermediate forms connecting them. In a ring species:
- A ring of populations encircles an area of unsuitable habitat.
- At one location in the ring of populations, two distinct forms coexist without interbreeding, and hence are different species.
- Around the rest of the ring, the traits of one of these species change gradually, through intermediate populations, into the traits of the second species.
A ring species, therefore, is a ring of populations in which there is only one place where two distinct species meet. Ernst Mayr called ring species "the perfect demonstration of speciation" because they show a range of intermediate forms between two species. They allow us to use variation in space to infer how changes occurred over time. This approach is especially powerful when we can reconstruct the biogeographical history of a ring species, as has been done in two cases. Source
I hate to bombard people with long posts, but maybe you should pay attention. There have been a number of observed instances of contemporary speciation. This partial list comes from the excellent talk.origins resource:5.0 Observed Instances of Speciation
The following are several examples of observations of speciation.
(See also the discussion in de Wet 1971).
While studying the genetics of the evening primrose, Oenothera lamarckiana, de Vries (1905) found an unusual variant among his plants. O. lamarckiana has a chromosome number of 2N = 14. The variant had a chromosome number of 2N = 28. He found that he was unable to breed this variant with O. lamarckiana. He named this new species O. gigas.
Digby (1912) crossed the primrose species Primula verticillata and P. floribunda to produce a sterile hybrid. Polyploidization occurred in a few of these plants to produce fertile offspring. The new species was named P. kewensis. Newton and Pellew (1929) note that spontaneous hybrids of P. verticillata and P. floribunda set tetraploid seed on at least three occasions. These happened in 1905, 1923 and 1926.
Owenby (1950) demonstrated that two species in this genus were produced by polyploidization from hybrids. He showed that Tragopogon miscellus found in a colony in Moscow, Idaho was produced by hybridization of T. dubius and T. pratensis. He also showed that T. mirus found in a colony near Pullman, Washington was produced by hybridization of T. dubius and T. porrifolius. Evidence from chloroplast DNA suggests that T. mirus has originated independently by hybridization in eastern Washington and western Idaho at least three times (Soltis and Soltis 1989). The same study also shows multiple origins for T. micellus.
The Russian cytologist Karpchenko (1927, 1928) crossed the radish, Raphanus sativus, with the cabbage, Brassica oleracea. Despite the fact that the plants were in different genera, he got a sterile hybrid. Some unreduced gametes were formed in the hybrids. This allowed for the production of seed. Plants grown from the seeds were interfertile with each other. They were not interfertile with either parental species. Unfortunately the new plant (genus Raphanobrassica) had the foliage of a radish and the root of a cabbage.
A species of hemp nettle, Galeopsis tetrahit, was hypothesized to be the result of a natural hybridization of two other species, G. pubescens and G. speciosa (Muntzing 1932). The two species were crossed. The hybrids matched G. tetrahit in both visible features and chromosome morphology.
Along similar lines, Clausen et al. (1945) hypothesized that Madia citrigracilis was a hexaploid hybrid of M. gracilis and M. citriodora As evidence they noted that the species have gametic chromosome numbers of n = 24, 16 and 8 respectively. Crossing M. gracilis and M. citriodora resulted in a highly sterile triploid with n = 24. The chromosomes formed almost no bivalents during meiosis. Artificially doubling the chromosome number using colchecine produced a hexaploid hybrid which closely resembled M. citrigracilis and was fertile.
Frandsen (1943, 1947) was able to do this same sort of recreation of species in the genus Brassica (cabbage, etc.). His experiments showed that B. carinata (n = 17) may be recreated by hybridizing B. nigra (n = 8) and B. oleracea, B. juncea (n = 18) may be recreated by hybridizing B. nigra and B. campestris (n = 10), and B. napus (n = 19) may be recreated by hybridizing B. oleracea and B. campestris.
Rabe and Haufler (1992) found a naturally occurring diploid sporophyte of maidenhair fern which produced unreduced (2N) spores. These spores resulted from a failure of the paired chromosomes to dissociate during the first division of meiosis. The spores germinated normally and grew into diploid gametophytes. These did not appear to produce antheridia. Nonetheless, a subsequent generation of tetraploid sporophytes was produced. When grown in the lab, the tetraploid sporophytes appear to be less vigorous than the normal diploid sporophytes. The 4N individuals were found near Baldwin City, Kansas.
Woodsia abbeae was described as a hybrid of W. cathcariana and W. ilvensis (Butters 1941). Plants of this hybrid normally produce abortive sporangia containing inviable spores. In 1944 Butters found a W. abbeae plant near Grand Portage, Minn. that had one fertile frond (Butters and Tryon 1948). The apical portion of this frond had fertile sporangia. Spores from this frond germinated and grew into prothallia. About six months after germination sporophytes were produced. They survived for about one year. Based on cytological evidence, Butters and Tryon concluded that the frond that produced the viable spores had gone tetraploid. They made no statement as to whether the sporophytes grown produced viable spores.
Speciation through hybridization and/or polyploidy has long been considered much less important in animals than in plants [[[refs.]]]. A number of reviews suggest that this view may be mistaken. (Lokki and Saura 1980; Bullini and Nascetti 1990; Vrijenhoek 1994). Bullini and Nasceti (1990) review chromosomal and genetic evidence that suggest that speciation through hybridization may occur in a number of insect species, including walking sticks, grasshoppers, blackflies and cucurlionid beetles. Lokki and Saura (1980) discuss the role of polyploidy in insect evolution. Vrijenhoek (1994) reviews the literature on parthenogenesis and hybridogenesis in fish. I will tackle this topic in greater depth in the next version of this document.
Gottlieb (1973) documented the speciation of Stephanomeira malheurensis. He found a single small population (< 250 plants) among a much larger population (> 25,000 plants) of S. exigua in Harney Co., Oregon. Both species are diploid and have the same number of chromosomes (N = 8). S. exigua is an obligate outcrosser exhibiting sporophytic self-incompatibility. S. malheurensis exhibits no self-incompatibility and self-pollinates. Though the two species look very similar, Gottlieb was able to document morphological differences in five characters plus chromosomal differences. F1 hybrids between the species produces only 50% of the seeds and 24% of the pollen that conspecific crosses produced. F2 hybrids showed various developmental abnormalities.
Pasterniani (1969) produced almost complete reproductive isolation between two varieties of maize. The varieties were distinguishable by seed color, white versus yellow. Other genetic markers allowed him to identify hybrids. The two varieties were planted in a common field. Any plant's nearest neighbors were always plants of the other strain. Selection was applied against hybridization by using only those ears of corn that showed a low degree of hybridization as the source of the next years seed. Only parental type kernels from these ears were planted. The strength of selection was increased each year. In the first year, only ears with less than 30% intercrossed seed were used. In the fifth year, only ears with less than 1% intercrossed seed were used. After five years the average percentage of intercrossed matings dropped from 35.8% to 4.9% in the white strain and from 46.7% to 3.4% in the yellow strain.
At reasonably low concentrations, copper is toxic to many plant species. Several plants have been seen to develop a tolerance to this metal (Macnair 1981). Macnair and Christie (1983) used this to examine the genetic basis of a postmating isolating mechanism in yellow monkey flower. When they crossed plants from the copper tolerant "Copperopolis" population with plants from the nontolerant "Cerig" population, they found that many of the hybrids were inviable. During early growth, just after the four leaf stage, the leaves of many of the hybrids turned yellow and became necrotic. Death followed this. This was seen only in hybrids between the two populations. Through mapping studies, the authors were able to show that the copper tolerance gene and the gene responsible for hybrid inviability were either the same gene or were very tightly linked. These results suggest that reproductive isolation may require changes in only a small number of genes.
Dobzhansky and Pavlovsky (1971) reported a speciation event that occurred in a laboratory culture of Drosophila paulistorum sometime between 1958 and 1963. The culture was descended from a single inseminated female that was captured in the Llanos of Colombia. In 1958 this strain produced fertile hybrids when crossed with conspecifics of different strains from Orinocan. From 1963 onward crosses with Orinocan strains produced only sterile males. Initially no assortative mating or behavioral isolation was seen between the Llanos strain and the Orinocan strains. Later on Dobzhansky produced assortative mating (Dobzhansky 1972).
Thoday and Gibson (1962) established a population of Drosophila melanogaster from four gravid females. They applied selection on this population for flies with the highest and lowest numbers of sternoplural chaetae (hairs). In each generation, eight flies with high numbers of chaetae were allowed to interbreed and eight flies with low numbers of chaetae were allowed to interbreed. Periodically they performed mate choice experiments on the two lines. They found that they had produced a high degree of positive assortative mating between the two groups. In the decade or so following this, eighteen labs attempted unsuccessfully to reproduce these results. References are given in Thoday and Gibson 1970.
Crossley (1974) was able to produce changes in mating behavior in two mutant strains of D. melanogaster. Four treatments were used. In each treatment, 55 virgin males and 55 virgin females of both ebony body mutant flies and vestigial wing mutant flies (220 flies total) were put into a jar and allowed to mate for 20 hours. The females were collected and each was put into a separate vial. The phenotypes of the offspring were recorded. Wild type offspring were hybrids between the mutants. In two of the four treatments, mating was carried out in the light. In one of these treatments all hybrid offspring were destroyed. This was repeated for 40 generations. Mating was carried out in the dark in the other two treatments. Again, in one of these all hybrids were destroyed. This was repeated for 49 generations. Crossley ran mate choice tests and observed mating behavior. Positive assortative mating was found in the treatment which had mated in the light and had been subject to strong selection against hybridization. The basis of this was changes in the courtship behaviors of both sexes. Similar experiments, without observation of mating behavior, were performed by Knight, et al. (1956).
Kilias, et al. (1980) exposed D. melanogaster populations to different temperature and humidity regimes for several years. They performed mating tests to check for reproductive isolation. They found some sterility in crosses among populations raised under different conditions. They also showed some positive assortative mating. These things were not observed in populations which were separated but raised under the same conditions. They concluded that sexual isolation was produced as a byproduct of selection.
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.
In a series of experiments, del Solar (1966) derived positively and negatively geotactic and phototactic strains of D. pseudoobscura from the same population by running the flies through mazes. Flies from different strains were then introduced into mating chambers (10 males and 10 females from each strain). Matings were recorded. Statistically significant positive assortative mating was found.
In a separate series of experiments Dodd (1989) raised eight populations derived from a single population of D. Pseudoobscura on stressful media. Four populations were raised on a starch based medium, the other four were raised on a maltose based medium. The fly populations in both treatments took several months to get established, implying that they were under strong selection. Dodd found some evidence of genetic divergence between flies in the two treatments. He performed mate choice tests among experimental populations. He found statistically significant assortative mating between populations raised on different media, but no assortative mating among populations raised within the same medium regime. He argued that since there was no direct selection for reproductive isolation, the behavioral isolation results from a pleiotropic by-product to adaptation to the two media. Schluter and Nagel (1995) have argued that these results provide experimental support for the hypothesis of parallel speciation.
Less dramatic results were obtained by growing D. willistoni on media of different pH levels (de Oliveira and Cordeiro 1980). Mate choice tests after 26, 32, 52 and 69 generations of growth showed statistically significant assortative mating between some populations grown in different pH treatments. This ethological isolation did not always persist over time. They also found that some crosses made after 106 and 122 generations showed significant hybrid inferiority, but only when grown in acid medium.
Some proposed models of speciation rely on a process called reinforcement to complete the speciation process. Reinforcement occurs when to partially isolated allopatric populations come into contact. Lower relative fitness of hybrids between the two populations results in increased selection for isolating mechanisms. I should note that a recent review (Rice and Hostert 1993) argues that there is little experimental evidence to support reinforcement models. Two experiments in which the authors argue that their results provide support are discussed below.
Ehrman (1971) established strains of wild-type and mutant (black body) D. melanogaster. These flies were derived from compound autosome strains such that heterotypic matings would produce no progeny. The two strains were reared together in common fly cages. After two years, the isolation index generated from mate choice experiments had increased from 0.04 to 0.43, indicating the appearance of considerable assortative mating. After four years this index had risen to 0.64 (Ehrman 1973).
Along the same lines, Koopman (1950) was able to increase the degree of reproductive isolation between two partially isolated species, D. pseudoobscura and D. persimilis.
The founder-flush (a.k.a. flush-crash) hypothesis posits that genetic drift and founder effects play a major role in speciation (Powell 1978). During a founder-flush cycle a new habitat is colonized by a small number of individuals (e.g. one inseminated female). The population rapidly expands (the flush phase). This is followed by the population crashing. During this crash period the population experiences strong genetic drift. The population undergoes another rapid expansion followed by another crash. This cycle repeats several times. Reproductive isolation is produced as a byproduct of genetic drift.
Dodd and Powell (1985) tested this hypothesis using D. pseudoobscura. A large, heterogeneous population was allowed to grow rapidly in a very large population cage. Twelve experimental populations were derived from this population from single pair matings. These populations were allowed to flush. Fourteen months later, mating tests were performed among the twelve populations. No postmating isolation was seen. One cross showed strong behavioral isolation. The populations underwent three more flush-crash cycles. Forty-four months after the start of the experiment (and fifteen months after the last flush) the populations were again tested. Once again, no postmating isolation was seen. Three populations showed behavioral isolation in the form of positive assortative mating. Later tests between 1980 and 1984 showed that the isolation persisted, though it was weaker in some cases.
Galina, et al. (1993) performed similar experiments with D. pseudoobscura. Mating tests between populations that underwent flush-crash cycles and their ancestral populations showed 8 cases of positive assortative mating out of 118 crosses. They also showed 5 cases of negative assortative mating (i.e. the flies preferred to mate with flies of the other strain). Tests among the founder-flush populations showed 36 cases of positive assortative mating out of 370 crosses. These tests also found 4 cases of negative assortative mating. Most of these mating preferences did not persist over time. Galina, et al. concluded that the founder-flush protocol yields reproductive isolation only as a rare and erratic event.
Ahearn (1980) applied the founder-flush protocol to D. silvestris. Flies from a line of this species underwent several flush-crash cycles. They were tested in mate choice experiments against flies from a continuously large population. Female flies from both strains preferred to mate with males from the large population. Females from the large population would not mate with males from the founder flush population. An asymmetric reproductive isolation was produced.
In a three year experiment, Ringo, et al. (1985) compared the effects of a founder-flush protocol to the effects of selection on various traits. A large population of D. simulans was created from flies from 69 wild caught stocks from several locations. Founder-flush lines and selection lines were derived from this population. The founder-flush lines went through six flush-crash cycles. The selection lines experienced equal intensities of selection for various traits. Mating test were performed between strains within a treatment and between treatment strains and the source population. Crosses were also checked for postmating isolation. In the selection lines, 10 out of 216 crosses showed positive assortative mating (2 crosses showed negative assortative mating). They also found that 25 out of 216 crosses showed postmating isolation. Of these, 9 cases involved crosses with the source population. In the founder-flush lines 12 out of 216 crosses showed positive assortative mating (3 crosses showed negative assortative mating). Postmating isolation was found in 15 out of 216 crosses, 11 involving the source population. They concluded that only weak isolation was found and that there was little difference between the effects of natural selection and the effects of genetic drift.
A final test of the founder-flush hypothesis will be described with the housefly cases below.
Meffert and Bryant (1991) used houseflies to test whether bottlenecks in populations can cause permanent alterations in courtship behavior that lead to premating isolation. They collected over 100 flies of each sex from a landfill near Alvin, Texas. These were used to initiate an ancestral population. From this ancestral population they established six lines. Two of these lines were started with one pair of flies, two lines were started with four pairs of flies and two lines were started with sixteen pairs of flies. These populations were flushed to about 2,000 flies each. They then went through five bottlenecks followed by flushes. This took 35 generations. Mate choice tests were performed. One case of positive assortative mating was found. One case of negative assortative mating was also found.
Soans, et al. (1974) used houseflies to test Pimentel's model of speciation. This model posits that speciation requires two steps. The first is the formation of races in subpopulations. This is followed by the establishment of reproductive isolation. Houseflies were subjected to intense divergent selection on the basis of positive and negative geotaxis. In some treatments no gene flow was allowed, while in others there was 30% gene flow. Selection was imposed by placing 1000 flies into the center of a 108 cm vertical tube. The first 50 flies that reached the top and the first 50 flies that reached the bottom were used to found positively and negatively geotactic populations. Four populations were established:
| Population A + geotaxis, | no gene flow |
| Population B - geotaxis, | no gene flow |
| Population C + geotaxis, | 30% gene flow |
| Population D - geotaxis, | 30% gene flow |
Selection was repeated within these populations each generations. After 38 generations the time to collect 50 flies had dropped from 6 hours to 2 hours in Pop A, from 4 hours to 4 minutes in Pop B, from 6 hours to 2 hours in Pop C and from 4 hours to 45 minutes in Pop D. Mate choice tests were performed. Positive assortative mating was found in all crosses. They concluded that reproductive isolation occurred under both allopatric and sympatric conditions when very strong selection was present.
Hurd and Eisenberg (1975) performed a similar experiment on houseflies using 50% gene flow and got the same results.
Recently there has been a lot of interest in whether the differentiation of an herbivorous or parasitic species into races living on different hosts can lead to sympatric speciation. It has been argued that in animals that mate on (or in) their preferred hosts, positive assortative mating is an inevitable byproduct of habitat selection (Rice 1985; Barton, et al. 1988). This would suggest that differentiated host races may represent incipient species.
Rhagoletis pomonella is a fly that is native to North America. Its normal host is the hawthorn tree. Sometime during the nineteenth century it began to infest apple trees. Since then it has begun to infest cherries, roses, pears and possibly other members of the rosaceae. Quite a bit of work has been done on the differences between flies infesting hawthorn and flies infesting apple. There appear to be differences in host preferences among populations. Offspring of females collected from on of these two hosts are more likely to select that host for oviposition (Prokopy et al. 1988). Genetic differences between flies on these two hosts have been found at 6 out of 13 allozyme loci (Feder et al. 1988, see also McPheron et al. 1988). Laboratory studies have shown an asynchrony in emergence time of adults between these two host races (Smith 1988). Flies from apple trees take about 40 days to mature, whereas flies from hawthorn trees take 54-60 days to mature. This makes sense when we consider that hawthorn fruit tends to mature later in the season that apples. Hybridization studies show that host preferences are inherited, but give no evidence of barriers to mating. This is a very exciting case. It may represent the early stages of a sympatric speciation event (considering the dispersal of R. pomonella to other plants it may even represent the beginning of an adaptive radiation). It is important to note that some of the leading researchers on this question are urging caution in interpreting it. Feder and Bush (1989) stated:
"Hawthorn and apple "host races" of R. pomonella may therefore represent incipient species. However, it remains to be seen whether host-associated traits can evolve into effective enough barriers to gene flow to result eventually in the complete reproductive isolation of R. pomonella populations."
Eurosta solidaginis is a gall forming fly that is associated with goldenrod plants. It has two hosts: over most of its range it lays its eggs in Solidago altissima, but in some areas it uses S. gigantea as its host. Recent electrophoretic work has shown that the genetic distances among flies from different sympatric hosts species are greater than the distances among flies on the same host in different geographic areas (Waring et al. 1990). This same study also found reduced variability in flies on S. gigantea. This suggests that some E. solidaginis have recently shifted hosts to this species. A recent study has compared reproductive behavior of the flies associated with the two hosts (Craig et al. 1993). They found that flies associated with S. gigantea emerge earlier in the season than flies associated with S. altissima. In host choice experiments, each fly strain ovipunctured its own host much more frequently than the other host. Craig et al. (1993) also performed several mating experiments. When no host was present and females mated with males from either strain, if males from only one strain were present. When males of both strains were present, statistically significant positive assortative mating was seen. In the presence of a host, assortative mating was also seen. When both hosts and flies from both populations were present, females waited on the buds of the host that they are normally associated with. The males fly to the host to mate. Like the Rhagoletis case above, this may represent the beginning of a sympatric speciation.
Halliburton and Gall (1981) established a population of flour beetles collected in Davis, California. In each generation they selected the 8 lightest and the 8 heaviest pupae of each sex. When these 32 beetles had emerged, they were placed together and allowed to mate for 24 hours. Eggs were collected for 48 hours. The pupae that developed from these eggs were weighed at 19 days. This was repeated for 15 generations. The results of mate choice tests between heavy and light beetles was compared to tests among control lines derived from randomly chosen pupae. Positive assortative mating on the basis of size was found in 2 out of 4 experimental lines.
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.
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.
Similar phenomena have been seen in a number of other insects. Microoganisms are seen in the eggs of both Nasonia vitripennis and N. giraulti. These two species do not normally hybridize. Following treatment with antibiotics, hybrids occur between them (Breeuwer and Werren 1990). In this case, the symbiont is associated with improper condensation of host chromosomes.
For more examples and a critical review of this topic, see Thompson 1987.
So far the BSC has applied to all of the experiments discussed. The following are a couple of major morphological changes produced in asexual species. Do these represent speciation events? The answer depends on how species is defined.
Boraas (1983) reported the induction of multicellularity in a strain of Chlorella pyrenoidosa (since reclassified as C. vulgaris) by predation. He was growing the unicellular green alga in the first stage of a two stage continuous culture system as for food for a flagellate predator, Ochromonas sp., that was growing in the second stage. Due to the failure of a pump, flagellates washed back into the first stage. Within five days a colonial form of the Chlorella appeared. It rapidly came to dominate the culture. The colony size ranged from 4 cells to 32 cells. Eventually it stabilized at 8 cells. This colonial form has persisted in culture for about a decade. The new form has been keyed out using a number of algal taxonomic keys. They key out now as being in the genus Coelosphaerium, which is in a different family from Chlorella.
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.
“Of course I’m sure creationists will have a ready retort, no matter how convoluted.”
Really no reason to do so friend. Those that hold to a “evolutionary” worldview won’t change their views, short of the miraculous. And those of us called “Creationists” won’t abandon our faith (I’m not ashamed to call it that).
So, the point is....Why continue to bother?
Sounds like a theory, not an example.
You’re looking at what IS in existance, and saying that one species developed into another.
NOT proof of speciation.
I’ve read of this observation before, and when the climate conditions changed back to “normal”, all the “species” differences also reverted to normal.
Sparky notes alter can't refute or address any of the quotes by experts that refutes his blind faith in evolution.
Even Gould knew that the fossil record refuted Darwin. Of course, you could always go with Gould's explanation -- evolution happened so fast, it didn't leave proof in the fossil record...But, then, we're supposed to believe it slowed down so it couldn't be observed.
“They may also yield insights into the first members of the human genus, Homo.”
Being facetious, I never cared much for being in the genus “Homo.” :-)
And how does this fit into the Creationist model? Where does it fit in between Adam and Eve and you?
All you need to do is conduct an experiment refutating some elemental part of evolution. Show, for instance, that differential survival is irrelevent to the relative frequencies of different genes in a population and you'd disprove natural selection. That would be very easy to do, and suddenly every scientist in the world would be searching for alternative models. No miracles are needed at all.
And those of us called “Creationists” won’t abandon our faith (I’m not ashamed to call it that).
I'm glad you call it faith. Because faith, rather than fact, calls you to your beliefs. There's not necessarily anything wrong in believing in something regardless of the facts, but it is important for creationists to understand that their beliefs are faith-based, not fact-based. That should inform public debates about whether creationism best belongs in a fact-based forum (a high school science class, for instance) or rather in a faith-based forum (a church or mosque).
Much better to ignore it completely or deny any possible evidence of evolution out of hand as the Creationists do?
You’re looking at what IS in existance, and saying that one species developed into another.
NOT proof of speciation.
Theory? All of the populations are living, and easily examined. No theory about it. You don't believe it, go and look for yourself.
You are going to extremes to deny evidence that is clear and convincing. It seems like you are doing creation "science" rather than real science.
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