I studied astronomy back in 1995, and one of the interesting things about
that was that the time frames weren't totally set. They were all give or
take 50 million years, and i think that some of the dates that people quote
now are different to the one's we were quoted then. This is not a matter of
mechanism, this is a simple "we don't really know...".
Another thing I studied had to do with dating methods, and how different
groups had dated a group of fossils from Indonesia and had come up with
totally different dates. This caused a huge contraversy about methods used
to date fossils. The point was that they didn't have a fool proof way of
dating, and so no side could show that they were right.
And the fossil record doesn't show much change, only on a small scale,
unless you have some hidden stash of fossils that could convince me, I
haven't seen much to catch my attention.
We don't know if it is possible for random change to improve an animal, so
I don't think at this stage in our understanding we could say that
evolution is a fact beyond the observable small scale evolution. The reason
mechanism is a big question is because we have no proof that the mechanisms
that run micro evolution can effect marco changes.
The fruit fly thing, it's interesting to note that sometimes all the
hybrids were killed, which makes variation less likely, as the gene pool is
reduced.
Donald
At 08:09 AM 23/07/98 -0700, you wrote:
>Donald Howes:
>What is this data from the lab that supports evolution? And what
>observations are you refering to that support evolution? Are you talking
>about something that we have seen happen, or something from the past that
we are speculating about as to how it happened? I think there are many
observable facts in nature that show a past but tell us nothing of how it
got there.>>
>
>RIght, we observe an evolving pattern in fossils for instance, we observe
similar patterns when looking at genetic 'distances' for instance. The data
supporting that 'evolution' happened is quite overwhelming. The remaining
question is, how does one explain the observations. Observations from the
past are as good as any btw.
>
>http://www.talkorigins.org/faqs/evolution-fact.html has some information
which can help here.
>
>It is time for students of the evolutionary process, especially those who
have been misquoted and used by the creationists, to state clearly that
evolution is a FACT, not theory, and that what is at issue within biology
are questions of details of the process and the relative importance
of different mechanisms of evolution. It is a FACT that the earth with
liquid water, is more than 3.6 billion years old. It is a FACT that
cellular life has been around for at least half of that period and
that organized multicellular life is at least 800 million years old. It is
a FACT that major life forms not on earth were not at all represented in
the past. There were no birds or mammals 250 million years ago. It is a
FACT that major life forms of the past are no longer living. There
used to be dinosaurs and Pithecanthropus, and there are none now. It is a
FACT that all living forms come from previous living forms. Therefore, all
present forms of life arose from ancestral forms that were different. Birds
arose from nonbirds and humans from nonhumans. No person who pretends to
any understanding of the natural world can deny these facts any more than
she or he can deny that the earth is round, rotates on its axis, and
revolves around the sun.
>
> The controversies about evolution lie in the realm of the relative
importance of various forces in molding evolution.
>
> - R. C. Lewontin "Evolution/Creation Debate: A Time for Truth"
Bioscience 31, 559 (1981) reprinted in Evolution versus Creationism, op cit.
>
>
>Or since the Fruit-fly was brought up (I apologize for the length)
>
>
>5.3 The Fruit Fly Literature
>
> 5.3.1 Drosophila paulistorum 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).
>
> 5.3.2 Disruptive Selection on Drosophila melanogaster 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.
>
> 5.3.3 Selection on Courtship Behavior in Drosophila melanogaster
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).
>
> 5.3.4 Sexual Isolation as a Byproduct of Adaptation to Environmental
Conditions in Drosophila melanogaster 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.
>
> 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.
>
> 5.3.6 Isolation Produced as an Incidental Effect of Selection on
several Drosophila species 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.
>
> 5.3.7 Selection for Reinforcement in Drosophila melanogaster 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.
>
> 5.3.8 Tests of the Founder-flush Speciation Hypothesis Using Drosophila
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.
>
>
>
>