The page on pathlights.com entitled "Fruit Flies Speak Up" purports to show that "evolution is a fake" by examining experiments with the popular lab animal, the fruit fly Drosophila melanogaster. Since I did my Ph.D. on evolution in Drosophila melanogaster and its close relatives, I was surprised to hear this species held up as proof that "evolution is a fake." In any case, the authors of the "Fruit Flies Speak Up" page (which is supposedly an excerpt from the book Mutations available through pathlights.com) have made 14 major claims on this page, and have used quotations (some from creationists, some from evolutionary biologists) to bolster their claim that fruit fly experiments prove that "evolution is a fake." I will go through each of the 14 claims in turn. If the pathlights page presented a quote to supposedly bolster their claim, then I have reprinted that quote here, followed by my response to the claim. Jason Hodin Seattle, WA USA
[email protected] CLAIM 1: X-rays have been used to catalyze...the fruit fly evolutionary process CLAIM 2: Even with this tremendous speedup of mutations, scientists have not been able to come up with anything other than another fruit fly.
CLAIM 3: A new species is never produced: The fruit flies always remain fruit flies. CLAIM 4: A thousand known fruit-fly mutations placed in one individual would still not produce a new species! CLAIM 5: Fruit flies refuse to become anything but fruit flies under any circumstances yet devised CLAIM 6: Fruit flies which receive mutations are always weakened in one way or another.
CLAIM 7: The mutated creatures die out, when placed out in nature with normal hardy specimens.
CLAIM 8: The mutated offspring are always constitutionally weaker than their parent form or species
CLAIM 9: The classical example of the damaging effects of mutations is to be found in what scientists have done to fruit flies by inducing mutations in them. CLAIM 10: No new species of fruit flies have ever resulted from sixty years of irradiation the poor creatures.
CLAIM 11: Notice the fact that, in those instances in which damaged fruit flies survive long enough, they change back into regular fruit flies - even those without eyes!
CLAIM 12: There is yet no evidence that when genes have accidents (called mutations), that is for the better. CLAIM 13: One experiment produced fruit flies without eyes. Yet, after a few life cycles, flies with eyes began to appear. Some kind of genetic repair mechanism took over and blocked any possibility of evolution. CLAIM 14: A fruit fly will always be a fruit fly CLAIM 1: X-rays have been used to catalyze...the fruit fly evolutionary process Fruit fly generations have been studied longer than the presumed time man has been on earth. According to evolution, man has lived on the earth for a little over a million years. Yet experiments on fruit flies have already exceeded the equivalent of a million years of people living on earth. Here is a clear statement of the problem: "The fruit fly has long been the favorite object of mutational experiments because of its fast gestation period [twelve days]. X rays have been used to increase the mutation rate in the fruit fly by 15,000 percent. All in all, scientists have been able to "catalyze the fruit fly evolutionary process, such that what has been seen to occur in Drosophila is the equivalent of the many millions of years of normal mutations and evolution." FACT: The x-ray mutagenesis experiments alluded to do not mimic the evolutionary process for two reasons. #1 - the major source of variation in organisms is not mutation, it’s recombination (see note 1) (mixing and matching different versions of genes during the process of sexual reproduction – that's why no two humans - except identical twins - are genetically alike). #2 - furthermore, as I'll mention in more detail below, most mutations are either harmful or neutral (no obvious effect). A very small percentage of mutations are beneficial. The mutagenesis experiments alluded to are not directed at finding beneficial mutations. In fact, these experiments are essentially designed to produce total “freaks” - things that never would occur in nature because they are so obviously not beneficial. For example, flies have two wings. Mutations can create “freak” flies with four wings. This does not even bear on the question of the origin of species, so to suggest that these experiments are designed (or can even be interpreted) to confirm or deny Darwinian ideas of species origins is disingenuous (see also CLAIM 3). CLAIM 2: Even with this tremendous speedup of mutations, scientists have not been able to come up with anything other than another fruit fly. Most important, what all these experiments demonstrate is that the fruit fly can vary within certain upper and lower limits but will never go beyond them. For example, Ernst Mayr reported on two experiments performed on the fruit fly back in 1948.
In the first experiment, the fly was selected for a decrease in bristles and, in the second experiment, for an increase in bristles. Starting with a parent stock averaging 36 bristles, it is possible after thirty generations to lower the average to 25 bristles, "but then the line became sterile and died out." In the second experiment, the average number of bristles was increased from 36 to 56; then sterility set in. Mayr concluded with the following observation: "Obviously any drastic improvement under selection must seriously deplete the store of genetic variability. The most frequent correlated response of one-sided selection is a drop in general fitness. This plagues virtually every breeding experiment." -Jeremy Rifkin, Algeny (1983), p. 134. FACT: These are interesting quotes from a father of modern evolutionary thought, but entirely irrelevant to the topic at hand. Note that the authors here choose not to explain the subtle genetic concepts that Mayr introduces. So let me take a crack at it (though this Mayr quote is presented almost entirely devoid of its context, so it is a bit difficult to interpret): Breeding experiments that focus on strong, rapid selection for a given characteristic, while paying no heed to possible harmful (harmful, that is, to organism "general fitness" - i.e. reproductive output) side consequences, will invariably yield flies that have reduced fitness. That such an artificial selection process (in this case, altering the number of sensory structures -bristles- on the body) ends up producing flies with reduced fitness is not at all surprising. Take this as an analogy. If one selects for dogs through classical breeding that have huge or tiny ears, you'll probably end up with a dog that would not fare well in the wild. Sensory bristles are a key characteristic for the proper functioning of a fly. The numbers of bristles in a fly has presumably been molded by natural selection to yield something close to an optimum in its natural environmental context. Is it any surprise that scientists in the lab cannot produce more fit organisms than millions of years of natural selection have produced? No, this is not at all surprising. CLAIM 3: A new species is never produced: The fruit flies always remain fruit flies. After decades of study, without immediately killing or sterilizing them, 400 different mutational features have been identified in fruit flies. But none of these changes the fruit fly to a different species. "Out of 400 mutations that have been provided by Drosophila melanogaster, there is not one that can be called a new species. It does not seem, therefore, that the central problem of evolution can be solved by mutations."*Maurice Caullery, Genetics and Heredity (1964), p. 119. FACT: Analyses of closely related species of fruit flies show that the genetic differences between these species are several orders of magnitude larger than "400". And the key thing here is that it's not just any "400" genetic differences anyway. Each one has to be able to produce a fly that is fully functional (when compared to the fly that you started with). These 400 mutations (see note 2), as I stated above, have not been generated to try to produce fully functional flies. Indeed, the goal is to produce “freak” flies so that one can begin to understand what the function of the un-mutated gene is. Geneticists mutate genes to see what defects are caused. The defects that are caused by a specific mutation will help indicate what the function of that gene is when it is in its "normal" (un-mutated) state. For example, a mutation that yields a fly with no eyes indicates that this gene is normally involved in eye production. If a given mutation produces no defects, then the vast majority of biologists are not interested in that mutation for two main reasons. 1) most geneticists are not testing evolutionary ideas with their experiments;
2) it's difficult to track the inheritance of mutations that have no effect, since how would you know if a given fly carried that mutation? There are ways, but they generally involve complex (and expensive and time consuming) molecular biology techniques. Most geneticists are not interested in doing such experiments. Some are, though! See below... In other words, this is a case of apples and oranges: the motivations of fruit fly geneticists for generating the mutations alluded to here had nothing to do with evolution. It sounds, though, like the authors of this article should consider funding or undertaking or at least proposing such research. That would allow them to suggest ways to actually test their hypotheses. CLAIM 4: A thousand known fruit-fly mutations placed in one individual would still not produce a new species! "Richard Goldschmidt fell into despair. The changes, he lamented, were so hopelessly micro [insignificant] that if a thousand mutations were combined in one specimen, there would still be no new species." -Norman Macbeth, Darwin Retried (1971), p. 33. FACT: Quite right. “A thousand known fruit-fly mutations placed in one individual” would certainly produce a dead fly. In other words, these are not the right kinds of genetic changes to study the question that is being addressed here. And – here's the key - nobody has to my knowledge claimed that these experiments as described were designed to test the hypothesis that multiple mutations would produce a new species. In other words, the authors of this article are debunking an argument that nobody would ever make! The term for such an argument is "straw man."
CLAIM 5: Fruit flies refuse to become anything but fruit flies under any circumstances yet devised
-Francis Hitching, The Neck of the Giraffe: Where Darwin Went Wrong (1982), p. 61 "In the best-known organisms, like Drosophila, innumerable mutants are known. If we were able to combine a thousand or more of such mutants in a single individual, this still would have no resemblance whatsoever to any type known as a [new] species in nature." -Richard B. Goldschmidt, "Evolution, As Viewed by One Geneticist," American Scientist, January 1952, p. 94. FACT: It is important to point out something here: evolutionary biologists have established that the most closely related species to Drosophila melanogaster fruit flies (the lab species) are...are you ready?...other Drosophila fruit flies! In fact, the evolutionary history of (known) fruit flies includes hundreds of described species with a history of greater than 60 million years (see note 3). If one were to generate a "new" species of fruit fly starting with Drosophila melanogaster, then the most reasonable hypothesis is that it would look something like its most closely related sister species, such as Drosophila simulans, Drosophila mauritiana or Drosophila sechellia. And what do these species look like? Almost indistinguishable from Drosophila melanogaster! Only an expert can tell them apart (see note 4). So why are they called different species? When you try to interbreed them, they either won't mate, or, if they do, they won't produce living and/or fertile offspring. That's the definition of "new species," not the production of "something other than a fruit fly." See also:
http://www.talkorigins.org/indexcc/CB/CB910_1.html CLAIM 6: Fruit flies which receive mutations are always weakened in one way or another. FACT: It is certainly true that many mutations, as I noted above, are harmful. These are selected against in nature. Very, very few are beneficial. Most, though, are so-called "neutral" mutations (see note 5). They have no discernable effect on fitness. What role such "neutral" mutations play in evolution is a subject of controversy, but the fact that these mutations exist is undeniable. Still, as I noted and explained above, most mutations that geneticists study are harmful. Such mutations can tell you something useful about the way in which fruit flies are built, but are not very useful in understanding evolution. So for the authors of this essay to suggest that such mutations might tell us something about mechanisms of species evolution is simply comparing apples and oranges. CLAIM 7: The mutated creatures die out, when placed out in nature with normal hardy specimens.
"The clear-cut mutants of Drosophila, with which so much of the classical research in genetics was done, are almost without exception inferior to wild-type flies in viability, fertility, longevity." -Theodosius Dobzhansky, Heredity and the Nature of Man (1964), p. 126.
FACT: Of course this is the case! See my explanation above regarding the Mayr quote on bristle number (CLAIM 2). CLAIM 8: The mutated offspring are always constitutionally weaker than their parent form or species
"A review of known facts about their ability to survive has led to no other conclusion than that they [the mutated offspring] are always constitutionally weaker than their parent form or species, and in a population with free competition they are eliminated. Therefore they are never found in nature (e.g. not a single one of the several hundred [types] of Drosophila mutation), and therefore, they are able to appear only in the favorable environment of the experimental field or laboratory." -H. Nilsson, Synthetische Artbildng (1957), p. 1186.
FACT: Let me reintroduce the concept of genetic recombination through sexual reproduction. That is the major source of variation in natural populations (see note 1) - the raw material of evolution by natural selection. Recombinationally-produced variants are much more likely to survive and be fit than mutationally-produced variants.
The occasional mutationally-produced variant is, indeed, beneficial (in the context of a given environment, that is). This has been most clearly demonstrated experimentally with E. coli bacteria (see note 6). In bacteria, one can start with a completely genetically homogeneous population of individuals. Any variation that occurs subsequent to that point can be unambiguously traceable to mutation. Then, selection experiments can be (and have been) done to demonstrate that certain mutational variants are favored over others, depending on the environment. This is precisely what Darwin predicted in Origin of Species, chapter 4. Finally, a recent modeling study (see note 7) has produced the intriguing observation that new variants that were slightly harmful on their own, acted as “stepping stones” to evolve increases in complexity. CLAIM 9: The classical example of the damaging effects of mutations is to be found in what scientists have done to fruit flies by inducing mutations in them.
"Most mutants which arise in any organism are more or less disadvantageous to their possessors.”
-Theodosius Dobzhansky, Evolution, Genetics, and Man (1955), p. 105. FACT: Note the difference between this quote by Dobzhansky (a famous evolutionary geneticist who studied the evolution of various different species of fruit flies), and the wording of the authors. The authors wrote (my emphasis): Fruit flies which receive mutations are always weakened in one way or another. Now, contrast this with Dobzhansky's wording: Most mutants which arise in any organism are more or less disadvantageous to their possessors.
I cannot stress enough the importance of the difference between the words "most...more or less" and "are always." Note how the authors try to look balanced in their selective, misleading, out of context or simply irrelevant use of quotes by respected scientists
The authors go on to quote extensively from the same Dobzhansky passage:
The classical mutants obtained in Drosophila usually show deterioration, breakdown, or disappearance of some organs. Mutants are known which diminish the quantity or destroy the pigment in the eyes, and in the body reduce the wings, eyes, bristles, legs. Many mutants are, in fact lethal to their possessors. Mutants which equal the normal fly in vigor are a minority, and mutants that would make a major improvement of the normal organization in the normal environments are unknown. So I assume that by providing this quote, the authors now at least admit that neutral mutations are possible! Even so, Dobzhansky (who did not have access to modern molecular techniques) clearly underestimated the propensity of "neutral" mutations (see note 5). In any case, neutral mutations are a key phenomenon that the authors ignore throughout the rest of the page, and in their own text.
As for the final sentence, all Dobzhansky is saying is what I stated earlier (see CLAIM 2): Is it any surprise that scientists in the lab cannot produce more fit organisms than millions of years of natural selection have produced? No, this is not at all surprising. Now, and here's the rub, if instead of "normal environments" we place such flies in novel environments, then such improvements are possible, and have, indeed, been produced in the lab (see note 8).
CLAIM 10: No new-species of fruit flies have ever resulted from sixty years of irradiating the poor creatures. "It is a striking, but not much mentioned fact that, though geneticists have been breeding fruit flies for sixty years or more in labs all round the world -flies which produce a new generation every eleven days- they have never yet seen the emergence of a new species or even a new enzyme." -Gordon R. Taylor, The Great Evolution Mystery (1983), p. 48. FACT: As far as I know, no-one has identified a "new enzyme" in any species of fly closely related to Drosophila melanogaster. What researchers have identified are new variants of enzymes (or other non-enzymatic proteins). That's even something that you can see in different populations of Drosophila species from around the world (see note 9). The consensus view is that evolution does not generally involve the appearance of new enzymes/proteins, but, instead, the evolution of novel types and novel usages of existing enzymes/proteins. In fact, the full complement of enzymes/proteins in fruit flies is largely the same as the full complement of enzymes/proteins in humans (see note 10). Evolution by natural selection is all about reshuffling the deck. See also CLAIM 5.
CLAIM 11: Notice the fact that, in those instances in which damaged fruit flies survive long enough, they change back into regular fruit flies - even those without eyes!
FACT: Of course they do! All of the known species of living fruit flies have eyes!!
And this would be no surprise to Darwin or Wallace (the other father of natural selection, a contemporary of Darwin), who clearly stated and accounted for this idea of reversion to the original type (see note 11).
CLAIM 12: There is yet no evidence that when genes have accidents (called mutations), that is for the better. FACT: This is such a common claim, I'm just going to refer here to another page on Talk.Origins Archives:
http://www.talkorigins.org/indexcc/CB/CB101.html CLAIM 13: One experiment produced fruit flies without eyes. Yet, after a few life cycles, flies with eyes began to appear. Some kind of genetic repair mechanism took over and blocked any possibility of evolution. FACT: The "genetic repair mechanism" is simple: fruit flies without eyes are far less fit than fruit flies with eyes, so of course they reverted to the original type! See CLAIM 11.
CLAIM 14: A fruit fly will always be a fruit fly
FACT: There are many different species of fruit flies, all with subtle but important differences from other fruit fly species. One would not expect to yield anything other than a fruit fly in lab experiments when that is the way that things happen in nature as well.
In sum, nothing in this article actually addresses the question: how might new species arise in nature? There is a huge scientific literature on this subject, and an overwhelming amount of good evidence that new species result from evolution by natural selection. See the following page on Talk.Origins Archives:
http://www.talkorigins.org/indexcc/CB/CB910.html ________________ [1] Feil EJ, Maiden MC, Achtman M, Spratt BG (1999) The relative contributions of recombination and mutation to the divergence of clones of Neisseria meningitidis. Mol Biol Evol. 16(11):1496-502. 2 actually, there are many more as of 2004; see
http://www.flybase.org/ 3 Grimaldi DA (1990) A phylogenetic, revised classification of Genera in the Drosophilidae (Diptera) Bulletin of the American Museum of Natural History. New York: New York. American Museum of Natural History. 4 Ashburner, M. 1989. Drosophila. Cold Spring Harbor, NY : Cold Spring Harbor Laboratory. 5 Papadopoulos D, Schneider D, Meier-Eiss J, Arber W, Lenski RE, Blot M (1999) Genomic evolution during a 10,000-generation experiment with bacteria. Proc Natl Acad Sci USA 96(7):3807-12. see also:
http://www.talkorigins.org/indexcc/CB/CB101.html 6 see the recent impressive work of Dr. Richard Lenski
7 Lenski RE, Ofria C, Pennock RT, and Adami C. (2003) The evolutionary origin of complex features. Nature 423:139-144. 8 see, for example: Cohan FM, Hoffmann AA (1986) Genetic divergence under uniform selection. II. Different responses to selection for knockdown resistance to ethanol among Drosophila melanogaster populations and their replicate lines. Genetics 114(1): 145-64. 9 see, for example: Saavedra CCR, Napp M, Reguly ML, Valente VLS (2001) Isoenzymatic polymorphisms in urban populations of Drosophila willistoni Rev Chil His Nat 74(1): 47-53. 10 Mushegian AR, Garey JR, Martin J, Liu L (1998) Large-scale taxonomic profiling of eukaryotic model organisms: a comparison of orthologous proteins encoded by the human, fly, nematode, and yeast genomes. Genome Research 8: 590-598. 11 Darwin addressed this concept in Origin of Species, Chapter 5; Alfred Russel Wallace addressed it in his Ternate Essay (1858)
Stumble It!
Tweet This
Bookmark on Delicious
Share on Facebook
Share on MySpace