colby@bu-bio.bu.edu (Chris Colby) (04/22/91)
In article <47570@ut-emx.uucp> bill@ut-emx.uucp (Bill Jefferys) writes: >In article <79788@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes: >#In article <18637@csli.Stanford.EDU> cphoenix@csli.Stanford.EDU (Chris Phoenix) writes: >#>Is this totally off base, or is non-genetic evolution a possibility? ># It's totally off base ;-) Non-genetic evolution is an >#oxymoron. >Actually, Chris P. is not so far off as one might think. >_The Economist_ had a story this week (in the science section) >about a certain species of wasp that reproduced parthenogenetically; >all of the offspring are female. Yet, if the wasps are fed >antibiotics, they will produce males and females in 50% >ratio. Why? It appears that a bacterium has co-evolved >with the wasp. It is transmitted via the eggs (see Chris >P's speculation above!!!), and has evolved the ability to >supress the production of male offspring. Presumably this >is because it provides an advantage to the bacterium! Yes, I read this when it came out in the literature. There are also wasp species that can interbreed when fed antibiotics, but not when they have the internal bacteria present. Interesting stuff. >Yet the wasp retains the ability to produce males, so it >is the _conditions_ under which the embryo develops >that determine the sex. A non-genetic "evolution" that >"breeds true" as long as the bacterium is present. You are confusing the process of evolution with simple change. If the gene pool of the wasps did not change (ie there are still the same frequency of male and female determining genes), then the population did not evolve. This is true even if there are more females than males compared to some time in the past. Let me give an example to illustrate my point. Humans have been growing larger and heavier in recent historical times. But this is not an evolutionary change; it is a result of better nutrition and medicine. If the environment returned to old conditions, humans would be shorter and thinner. In other words the genes have stayed the same (roughly), but the mani- festation of them has changed. The same is true in the wasps; the gene pool has not changed (or at least we'll assume it hasn't for the sake of argument) but the expression of the genes has changed due to a change in environment (presence of an internal endosymbiont). They have changed, but they haven't evolved. Remember that evolution is _defined_ as a change in the gene pool; therefore non-genetic evolution is by definition non- sensical. Populations phenotypes (expression of genes) can change without the gene pool changing. This can often be very interesting (as in the wasp case), but it is not evolution. >Bill Jefferys Chris Colby email: colby@bu-bio.bu.edu
bill@ut-emx.uucp (Bill Jefferys) (04/22/91)
In article <79798@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes: #In article <47570@ut-emx.uucp> bill@ut-emx.uucp (Bill Jefferys) writes: # #>Yet the wasp retains the ability to produce males, so it #>is the _conditions_ under which the embryo develops #>that determine the sex. A non-genetic "evolution" that #>"breeds true" as long as the bacterium is present. # # You are confusing the process of evolution with simple #change. If the gene pool of the wasps did not change (ie there #are still the same frequency of male and female determining #genes), then the population did not evolve. This is true even #if there are more females than males compared to some time in #the past.... Well, I _did_ put quotes around the word "evolution" in my post, so I am not confused. # Remember that evolution is _defined_ as a change in the #gene pool; therefore non-genetic evolution is by definition non- #sensical. Populations phenotypes (expression of genes) can change #without the gene pool changing. This can often be very interesting #(as in the wasp case), but it is not evolution. Well, Darwin would not have understood this definition of evolution, as the concepts "gene" and "gene pool" postdate him by a considerable time. For Darwin, evolution meant "descent with modification." You may decide for yourself whether this applies to the wasp example. Bill Jefferys -- If you meet the Buddha on the net, put him in your kill file --Robert Firth
cphoenix@csli.Stanford.EDU (Chris Phoenix) (04/25/91)
In article <79798@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes: > You are confusing the process of evolution with simple >change. If the gene pool of the wasps did not change (ie there >are still the same frequency of male and female determining >genes), then the population did not evolve. This is true even >if there are more females than males compared to some time in >the past. This is getting away from my question, but what do you consider the gene pool? If the bacteria mutated and this caused some change in the wasp, would you say the wasp had mutated? If you say "no", I have another question: would you say that we mutate if our mitochondria mutate? But the last theory I heard was that mitochondria used to be bacteria that our cells took in, once upon a time. (Bill, I wrote this just before I got your mail. I'll let it stand as a question to others, if they're interested.) Let me give an example to illustrate my point. > Humans have been growing larger and heavier in recent >historical times. But this is not an evolutionary change; it >is a result of better nutrition and medicine. This is an extracellular change. Obviously it is not a characteristic of the individual cells (ie if you pulled a cell out of Plato and a cell out of me and grew them in vitro you probably couldn't tell the difference in their offspring.) I am not interested in this kind of change. On the other hand, Discover did an article about the effects of malnutrition in the womb, in wartime Poland I believe. If the first generation went hungry while the second generation was a few-month-old fetus, then effects would be seen in the second *and* third generation, even though the third had normal nutrition. But I am interested in *intracellular* changes which do not involve the cell's nucleic acid, and preferably do not involve any nucleic acid. Let me give you a hypothetical example that typefies what I am looking for: Suppose a cell has a structure of tubules. These tubules serve as conveyors for various molecules, including some molecule necessary to build the tubules. So when the cell divides, the tubules grow and then the structure splits. If the structure were removed, it would no longer be able to grow (and thus couldn't start growing) since it was necessary for its own growth. Assuming the cell was still viable, its offspring would not have that structure. (I've left a lot of loose ends in this example, but I hope you see what I mean.) >Populations phenotypes (expression of genes) can change >without the gene pool changing. This can often be very interesting >(as in the wasp case), but it is not evolution. Should you distinguish between characteristics caused by expression of the genes and characteristics caused by the environment? Your human size example is entirely dependent on the environment. On a cellular level, changes caused by hormones are part of the environment and not part of the cell. But if you take a cell and its descendent, wash them carefully, and put them in petri dishes, and the offspring look different, that is not caused by the environment but by a transmissible change *inside the cell*. If that change does not involve nucleic acid, that is what I'm interested in. Speaking of hormones, I've been following the discussion on hormonal control of fetal growth with interest. But I haven't seen anyone address the question of where the hormones come from. I think all of them will be coded for by the DNA of the original fertilized egg. Assume that if you take one dinosaur cell, and one chicken cell with dinosaur DNA, and grow them in a dish, there is no difference in their phenotype. So a fertilized chicken-egg cell with dinosaur DNA will begin by producing dinosaur hormones. If these hormones spread through the growing embryo in the same way (which is purely based on the embryo's environment and physical structure) then the cells will react to them just like dinosaur cells would. So the embryo will keep developing like a dinosaur, and will become a dinosaur. Notice we've made several assumptions here. 1) The hybrid cells react exactly like dinosaur cells to all stimuli. 2) The embryo starts the same physically as a dinosaur embryo (eg. the original egg cell is the same size). 3) The environment is the same (eg. the pH of dinosaur yolk is the same as the pH of chicken yolk). I am interested in case 1), in whether a two cells with the same DNA will have the same phenotype--ie reaction to stimuli, internal structure, etc. I hope this is still interesting for people...
gagen@bgsuvax.UUCP (kathleen gagen) (04/25/91)
From article <79798@bu.edu.bu.edu>, by colby@bu-bio.bu.edu (Chris Colby): > > Remember that evolution is _defined_ as a change in the > gene pool; therefore non-genetic evolution is by definition non- > sensical. ORGANIC evolution is defined as a change in the gene pool. There are many other types of evolution. EVOLUTION means change. ie: the evolution of the solar system the evolution of western religious thought the evolution of Lake Erie. Kathi Gagen
mroussel@alchemy.chem.utoronto.ca (Marc Roussel) (04/26/91)
In article <79798@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes: > Remember that evolution is _defined_ as a change in the >gene pool; therefore non-genetic evolution is by definition non- >sensical. I'm not a biologist so I hope that what I'm about to write isn't total nonsense. If it is, reply by email and I will post a retraction with a summary of the points people have made. If not, we can debate things in this forum. It seems to me that the definition presented above is useful in some contexts, but overly restrictive in others. The wasp example which someone else posted is a good example. Whether or not the wasps' gene pool changed, there has been a change in the species which is persistent against (one presumes) significant external perturbations. It seems to me that this qualifies as evolution in a less restricted sense than the current dogma allows: a species can be said to have evolved a trait if this trait is transmissible from generation to generation and stable against reasonable environmental perturbations. (I will let someone else define "reasonable" and "external environment", if any of this makes sense. Surely in the case of the wasps and their symbiotic partners, the symbionts form one system and thus are not part of the external environment.) This definition of course excludes (quite rightly) trivial cases like the "better nutrition = taller humans" effect which Chris mentioned. My definition has the advantage that it allows us to include in evolutionary theory things which we may not have thought of yet. Further, stability of evolved traits as the hallmark of evolution brings the language of biology into line with modern thinking in other sciences. (I am curious to hear comments on this last point. Would people think of this as an advantage, a disadvantage, or neither?) I look forward to your comments. Marc R. Roussel mroussel@alchemy.chem.utoronto.ca
sarima@tdatirv.UUCP (Stanley Friesen) (04/28/91)
In article <1991Apr25.203311.20957@alchemy.chem.utoronto.ca> mroussel@alchemy.chem.utoronto.ca (Marc Roussel) writes: >... It seems to >me that this qualifies as evolution in a less restricted sense than the >current dogma allows: a species can be said to have evolved a trait if >this trait is transmissible from generation to generation and stable >against reasonable environmental perturbations. (I will let someone >else define "reasonable" and "external environment", if any of this >makes sense. I think it makes a certain amount of sense. The main reason for the current emphasis on the genetic component of change is because that is the one type of change we *know* is transmissible, as opposed to externally imposed. To Darwin, at least, the main point of evolution was the selection of heritable (== transmissible) changes (or variation). >Surely in the case of the wasps and their symbiotic partners, the >symbionts form one system and thus are not part of the external >environment.) This definition of course excludes (quite rightly) trivial >cases like the "better nutrition = taller humans" effect which Chris mentioned. An interesting sidelight her is that there *is* a genetic component in this system. The *symbiotic* *microbe* does in contain genes coding for lack of males in the wasp. (Shades of night - a gene in a microbe coding for a feature in its host?!?!). And this gene is certainly beneficial to the microbe, and is thus selected for. What is happening here appears to be a breakdown of the normal seperation between organisms. It is certainly admitted that at some point a former symbiont becomes a part of its host, at which point the distinction between 'genetic' and 'non-genetic' inheritance ceases to be meaningful. In the case of mitochondria and chloroplasts most of the genetic control has actually been transfered to the eukaryotic host (which is the other direction than the wasp example). Nonetheless there are a *few* traits that are still coded for in the organelle itself, leading to strange forms of 'cytoplasmic' inheritence. (Look at the 'Eve' studies in anthropoology). So, it gets quite interesting, the borders of things are actually quite fuzzy. Which is very normal in biology. -- --------------- uunet!tdatirv!sarima (Stanley Friesen)
colby@bu-bio.bu.edu (Chris Colby) (04/29/91)
In article <18844@csli.Stanford.EDU> cphoenix@csli.Stanford.EDU (Chris Phoenix) writes: >In article <79798@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes: >> You are confusing the process of evolution with simple >>change. If the gene pool of the wasps did not change (ie there >>are still the same frequency of male and female determining >>genes), then the population did not evolve. This is true even >>if there are more females than males compared to some time in >>the past. > >This is getting away from my question, but what do you consider the >gene pool? >If the bacteria mutated and this caused some change in the >wasp, would you say the wasp had mutated? (Depending on what you mean by change) No, I would say the environment (in this case an internal endosymbiont) caused a change in the expression of the wasps genes. >If you say "no", I have >another question: would you say that we mutate if our mitochondria >mutate? Good analogy, in this case I would say yes. Why the difference? Mitochondria and the rest of our cells are no longer autonomous; they each depend on each other for survival. I would say that now the gene pools count as one. In the wasp example, I don't know if the bacteria could live without the wasp, but the converse is certainly true. For that reason I would distinquish between the two gene pools. >But the last theory I heard was that mitochondria used to be >bacteria that our cells took in, once upon a time. (Bill, I wrote >this just before I got your mail. I'll let it stand as a question to >others, if they're interested.) Yes, this is the endosymbiotic theory. It is generally accepted. >Let me give an example to illustrate my point. >> Humans have been growing larger and heavier in recent >>historical times. But this is not an evolutionary change; it >>is a result of better nutrition and medicine. >This is an extracellular change. Obviously it is not a characteristic >of the individual cells (ie if you pulled a cell out of Plato and a >cell out of me and grew them in vitro you probably couldn't tell the >difference in their offspring.) I am not interested in this kind of >change. >But I am interested in *intracellular* changes which do not involve >the cell's nucleic acid, and preferably do not involve any nucleic >acid. Let me give you a hypothetical example that typefies what I am >looking for: Suppose a cell has a structure of tubules. These tubules >serve as conveyors for various molecules, including some molecule >necessary to build the tubules. If you could get the tubules to grow in vitro supplying only a nucleic acid free (or nucliec acid of random composition) cell extract then I would say it counts as a genetic component. IE. it contains the necessary info to replicate itself autonomously given the appropriate environment. I would think this would be synonomous with the mitochondrial example (mutual obligatory symbiosis). >Should you distinguish between characteristics caused by expression of >the genes and characteristics caused by the environment? Your human >size example is entirely dependent on the environment. Yes, one should distinguish between variation in a char- actoristic due to environmental and genetic factors; this is key to understanding evolution. In the human example, much of the variation through time could be ascribed to environment, but not all. Two short people are likely to have a short kid no matter how well you feed him/ her. >Speaking of hormones, I've been following the discussion on hormonal >control of fetal growth with interest. But I haven't seen anyone >address the question of where the hormones come from. I think all of >them will be coded for by the DNA of the original fertilized egg. Hormones are proteins coded for by genes. >So a fertilized chicken-egg cell with dinosaur DNA will >begin by producing dinosaur hormones. If these hormones spread >through the growing embryo in the same way (which is purely based on >the embryo's environment and physical structure) then the cells will >react to them just like dinosaur cells would. So the embryo will keep >developing like a dinosaur, and will become a dinosaur. The dinosaur DNA, however, would need the right cellular environment to function (ie correct transcription factors to activate the dinosaur genes, the appropriate equipment to pro- cess dinosaur mRNA once transcribed (ribosomes and factors)). A chicken cell may have diverged enough that it did not provide the right environment. I don't know, experiment hasn't been done. >I hope this is still interesting for people... So do I. Chris Colby email: colby@bu-bio.bu.edu
colby@bu-bio.bu.edu (Chris Colby) (04/29/91)
In article <1991Apr25.203311.20957@alchemy.chem.utoronto.ca> mroussel@alchemy.chem.utoronto.ca (Marc Roussel) writes: >In article <79798@bu.edu.bu.edu> colby@bu-bio.UUCP (Chris Colby) writes: >> Remember that evolution is _defined_ as a change in the >>gene pool; therefore non-genetic evolution is by definition non- >>sensical. > It seems to me that the definition presented above is useful in some >contexts, but overly restrictive in others. The wasp example which >someone else posted is a good example. Whether or not the wasps' gene >pool changed, there has been a change in the species which is persistent >against (one presumes) significant external perturbations. How does this differ (in the wasp case) from a persistent change in a species induced by an external parasite (for ex lower body weight due to the parasite tapping energy from the host)? Would you consider that an evolutionary change? (Hint: it isn't) [some stuff deleted] > My definition has the advantage that it allows us to include in >evolutionary theory things which we may not have thought of yet. So does the current definition. >Further, stability of evolved traits as the hallmark of evolution brings >the language of biology into line with modern thinking in other >sciences. You've been listening to creationists too long if you think evolutionary biology is lagging behind the other sciences. (Hint: go browse through recent copies of _Nature_ or _Science_ -big league science journals- and see if you see any articles about evolution. Hint: you will) >(I am curious to hear comments on this last point. Would people >think of this as an advantage, a disadvantage, or neither?) Evolved traits (since they are by definition genetically based) have been known to be stable since Mendel's work. > Marc R. Roussel Chris Colby email: colby@bu-bio.bu.edu