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Radical Evolution
Posted: 19 July 2005 03:47 PM   [ Ignore ]   [ # 16 ]  
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[quote author=“rabbit”]Bumper sticker:

The gene pool could use some chlorine!

  LOL

mhatter13, you may be right about the apparent lull in selection, but I think you over-estimate the strength of that variable.  If population growth continues and age demographics continue to skew, for example the aging of populations in the northern hemisphere and the decimation of mature adults due to rampant AIDS in Africa, global social instability will increase along with the likelihood of wars, including nuclear wars, and environmental disasters.  I think the chances of population isolation will increase.

Sorry I don’t have the issue in front of me, but the July 8 issue of Science has an interesting article re: the question “Are humans still evolving?”  Some interesting insights and speculations.

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Posted: 19 July 2005 06:26 PM   [ Ignore ]   [ # 17 ]  
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Evolution can be a very subtle and tricky thing to identify, so whether or not it is currently happening in humans is likely something that will be discovered by scientists in the future (by doing genetic drift analysis or something similar).

That having been said, I believe that evolution is happening, in people, right now, and I although I cannot prove it (unless someone wants to give me a few billion dollars in grant money), I think that I can make a decent enough case to convince people to at least remain open to the idea.

First, let’s define terms a little bit.  When I say that evolution is happening in humans, I mean that at its most elemental level, which is to say that some genes in the human genome are experiencing a shift in frequency as a result of selection pressure.  With that said, onwards and upwards.

The first bit of evidence that I would offer is that of changing environmental conditions.  The amount and type of polutants that the average person, in an industrialized setting, is likely to be exposed to, over their lifetime, is markedly different now than through most of human history.  That in and of itself would not mean too much, but there has been an increase in health problems that are easily linked to these environmental changes.  Although detractors often dismiss this, claiming that medicine counters these effects, it remains undeniable that many human beings die, before reaching reproductive age, as a result of these altered environmental conditions.  Inasmuch as these deaths are the result of negative genetic traits, I suspect that natural selection is at work.

Another argument that I would make involves disease, and specifically the evolution of disease, due to human activity.  As much as 90% of the Native American population was wiped out by ilness which hopped a ride to the New World in the bodies of European settlers.  Since then, as people have become increasingly mobile, there has been an increasing tendency to “share” our bugs with each other.  Our role in shaping disease is not limited to spreading it around though.  The rise of antibiotic resistant bacteria, for instance, is another thing that people are responsible for.  So, just as the European settlers had an undeniable impact on the genetics of Native Americans, the rise of so-called “super” bugs is, in my opinion, going to have an undeniable impact on the worlds genetics over the course of the next several generations.

Finally, I would like to point out that isolation can happen in a number of different ways.  There are many places in the US (not to mention elsewhere) where poverty spans generations.  Although we love success stories, the reality is that people don’t cross the tracks all that often, which means that people living less than a mile from each other can be as isolated as if they were on different islands with no boats.  It is also undeniable that poor people tend to live very different lives than rich people do.  Diet, health care, leisure activities, exposure to toxins, etc., etc., ad infinitum - these are all things that can have consequences, given someone’s genes.  If one considers the death rate amongst the male youth in the poorest urban neighborhoods, it is hard to imagine that selection of some sort isn’t happening.

So, to recap:  People are dying, and they are dying of different things than they would have been if people were still living as hunter-gatherers.  If enough of this new kind of dying is happening before people get a chance to reproduce, and the dying has a genetic component to it, then I contend that evolution is happening.  What I don’t pretend to know, is what the consequences of this evolution might be.  Will the human beings of 2200 AD be disease resistant supermen, able to survive on nothing but junk food?  Or will they be sickly slugs, unable to maintain even the most basic of life functions without extreme medical intervention?  I have no idea.  I do suspect, however, that if one were to take a random sampling of human beings, over the course of the last 10,000 years or so, the tale of genetic drift would be a fascinating one.

-Matt

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Posted: 20 July 2005 06:51 AM   [ Ignore ]   [ # 18 ]  
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Psionoclast - thanks for the post.  Interesting thread.  Not to come across as a dick, but I am curious as to your educational/professional background…  Think if it as an investigation before we give you those billions of dollars - not that I have a fraction of that to give!

I respectfully but strongly disagree w/ you, on most of your points - I think you 2200 AD comment gave you away.  No way humans in 200 yrs, or 2000, or even 20,000 are going to have “evolved” into supermen, slugs, or anything else.  Even if selection was occuring, your timescale is WAY off.  Also, you use alot of superlative but vague terms - “undeniable” is a favorite word of yours.  Show me the data - where is the proof that super-bugs are going to change human genetics in a couple of generations?  I think it is highly unlikely - they just don’t kill enough people, fast enough, to influence the evolution of humans.

And while I think your point about urban class isolation is quite true and very poetic, I think it has little if any effect on evolution.  Do you really feel that rich people are reproducing faster than poor, and only with other rich people?  Racial, economic, and cultural mixing is increasing, not decreasing, so separate species of rich and poor humans is NOT in the cards, based on current trends.  Remember, even a single mixing event is enough to screw up a genetic drift of one population from another.

I think a point people miss is that mutations alone don’t equal evolution - there must be strong selection forcing a particular mutation to increase within the population, due to a reproductive advantage, to say evolution is occuring.  I am not saying the gene pool in people isn’t changing - I’m sure it is.  But if more and more people survive and reproduce - w/ less and less selection, and less and less isolation, the gene pool will be bigger, but not not directed to move in any one way or another.

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Posted: 20 July 2005 09:15 AM   [ Ignore ]   [ # 19 ]  
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[quote author=“mhatter13”]Psionoclast - thanks for the post.  Interesting thread.  Not to come across as a dick, but I am curious as to your educational/professional background…  Think if it as an investigation before we give you those billions of dollars - not that I have a fraction of that to give!

I am a computer scientist, with a computer science background.  My knowledge of evolution is pretty much self taught, but my interest was sparked when I began using genetic algorithms to solve certain tricky problems.

I respectfully but strongly disagree w/ you, on most of your points - I think you 2200 AD comment gave you away.  No way humans in 200 yrs, or 2000, or even 20,000 are going to have “evolved” into supermen, slugs, or anything else.  Even if selection was occuring, your timescale is WAY off.  Also, you use alot of superlative but vague terms - “undeniable” is a favorite word of yours.  Show me the data - where is the proof that super-bugs are going to change human genetics in a couple of generations?  I think it is highly unlikely - they just don’t kill enough people, fast enough, to influence the evolution of humans.

My 2200 comment was not meant to be taken seriously, but you are forgetting punctuated equilibrium.  Critical changes do happen quickly, and epidemic outbreaks are the classic large scale killers.  The black plague in Europe single handedly shifted the average blood type of the people there, and it happened in a fairly short time.

So, to further drive the point home, we are tinkering with the evolution of our bugs, which will have an impact on our evolution.  I make no official prediction as to how long it will be before visible changes have occured.

And while I think your point about urban class isolation is quite true and very poetic, I think it has little if any effect on evolution.  Do you really feel that rich people are reproducing faster than poor, and only with other rich people?  Racial, economic, and cultural mixing is increasing, not decreasing, so separate species of rich and poor humans is NOT in the cards, based on current trends.  Remember, even a single mixing event is enough to screw up a genetic drift of one population from another.

Poor people generally outproduce rich people, not the other way around, and rich people do tend to stick with other rich people.  I don’t deny that sometimes rich and poor get together, but this tends to be a one-way deal.  Someone from a poor background “gets out” because of a desirable trait (beauty, intelligence, athletic prowess, etc.), and when they do get out, they tend not to look back.

I think a point people miss is that mutations alone don’t equal evolution - there must be strong selection forcing a particular mutation to increase within the population, due to a reproductive advantage, to say evolution is occuring.  I am not saying the gene pool in people isn’t changing - I’m sure it is.  But if more and more people survive and reproduce - w/ less and less selection, and less and less isolation, the gene pool will be bigger, but not not directed to move in any one way or another.

Perhaps you should have read my post more carefully.

[quote author=“psiconoclast”]First, let’s define terms a little bit. When I say that evolution is happening in humans, I mean that at its most elemental level, which is to say that some genes in the human genome are experiencing a shift in frequency as a result of selection pressure. With that said, onwards and upwards.

[quote author=“psiconoclast”]So, to recap: People are dying, and they are dying of different things than they would have been if people were still living as hunter-gatherers. If enough of this new kind of dying is happening before people get a chance to reproduce, and the dying has a genetic component to it, then I contend that evolution is happening.

-Matt

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Posted: 20 July 2005 10:07 AM   [ Ignore ]   [ # 20 ]  
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Psi -

Perhaps where we really differ is in our definition of “evolution.”  I don’t deny that mutations in the genome have occured, are occuring, and will continue to occur.  I also don’t deny that we are dying of different things then 20,000 or even 200 years ago.  But I challenge you to draw a concrete, clear connection between the two.  The ways we die now seem to have less, not more, to do w/ genes than ever before.  You actually point out this contradiction yourself - poor urban males may have a higher death rate than the average population, but their reproductive “fitness” is actually higher - they have as a group more children.  Will “superbugs” kill people in the future?  I agree with you that this is will most likely occur.  But will there be any selection based on genetics?  I’d say less likely than ever before.  Access to treatment will be far more important than say during the Middle Ages, when effective treatment was hard to come by.  Treatment access will be less related, if related at all, to genetics than old time “fitness.”  And massive die outs will be less likely - the breakouts will be contained, via quarantine and treatment.  Random mutations will not lead to “evolution” if the selection is random, too.  And selection is getting more random all the time…

For true evolution to occur, there can’t just be more white noise in the genome - there must be sustained selection pressure that forces the gene pool to move in one direction or another.  Put another way, we may have outpaced the role of genetics in selection.  Alot of the factors you point out - pollution, global travel, poverty - are very real public health concerns.  But relative to historical norms, we now live in a world were these things fluctuate rapidly - too quick for the gradual, persistant process of evolution to allow us adapt to them, particularly when selection based on even these factors is at an all time low.

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Posted: 20 July 2005 11:46 AM   [ Ignore ]   [ # 21 ]  
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Guest #2, the article in Science is in Vol. 309, No, 5732, pp 234-237.  It might be useful to this discussion.

For myself, if I were to speculate on likely scenarios, it would be one of two possibilities.  One would be not to far (though more biologically plausible) from the title of this thread.  In this scenario, humans develop some mastery of the evo-devo issues relevant to the human genome and start inserting new genetic elements to control the development of desired traits.  In other words, humans take over the role of Darwinian evolution by selection in causing the emergence of new genetics.  This scenario is problematic since it presuposes we humans are clever enough to predict which phenotypic or behavioral traits would be useful to future humans and that we do, in fact, figure out the detailed mechanisms.  However, a colleague of mine (known previously as gman) has actually been working on a version of this where the intent is to fiddle with the development of the prefrontal lobes in hopes of increasing the (for the moment we’ll call it) “wisdom” trait.  He has been studying the neuroscience behind what the psychologists who study wisdom have been finding and is pretty serious that it is something that could work out.  The idea is that increasing wisdom, unlike increasing say general intelligence, would actually benefit everyone and be a better basis for future decisions re: other traits to choose to enhance.

The other scenario follows some thinking that was posted in the science topic here some time back.  This has to do with the rate argument used above. Namely, the rate of destruction of the natural world will actually cause the mass extinction of many species and could seriously reduce the population of humans (if it doesn’t wipe us out) since we could not adapt rapidly enough.  The human line would then go through a bottleneck and if it succeeds would come out the other end in an efflorescence of species in the Homo line similar to the Cambrian explosion.  The reason this might be the case is that the factors which lead to the mixing of populations now (generally speaking - globalization) will not be possible in that distant future since all of the cheap (easily obtained) fuel will have been used up.

Well its fun to speculate, but I agree with mhatter13, it should be grounded in “current” understanding of evolution.  Matt, my understanding of genetic algorithms and evolutionary programming is that they are merely analogous to biological evolution and should not be taken too seriously as being the same thing.  They are both search algorithms in a large design space (to use Dennett’s terminology), one in problem space, the other in biological order space, but they do not really work in the same way. Just my $0.02

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Posted: 20 July 2005 01:50 PM   [ Ignore ]   [ # 22 ]  
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[quote author=“mhatter13”]Perhaps where we really differ is in our definition of “evolution.”  I don’t deny that mutations in the genome have occured, are occuring, and will continue to occur.  I also don’t deny that we are dying of different things then 20,000 or even 200 years ago.  But I challenge you to draw a concrete, clear connection between the two.

There are probably several that could be drawn, but I will focus on obesity.  Fairly recent changes in diet and behavior have lead to a substantial uptick in obesity.  Obese people (especially the morbidly obese) tend to die (of heart problems and the like) much earlier than average.  Although tracking down statistical info on the reproductive numbers of the morbidly obese vs. everyone else is hard to do, even if morbidly obese people reproduce at the average rate, the resulting loss of economic and other aid that they can provide their offspring should, according to your own “money is everything” stance, make a difference in the viability of people with the (recently discovered) gene for increased obesity/diabetes.  This, to me, is a clear case of modern changes in behavior resulting in unintended consequences for a subset of the population which is both gene-linked, and carries probable reproductive consequences.

The ways we die now seem to have less, not more, to do w/ genes than ever before.  You actually point out this contradiction yourself - poor urban males may have a higher death rate than the average population, but their reproductive “fitness” is actually higher - they have as a group more children.

Don’t put words into my mouth.  I never made any claims about the reproductive fitness of young urban men.  The truth may be a little bit different than you think.  Do women in the poorest urban environments have high pregnancy rates?  Sure.  Does this mean that they are all being impregnated by an equal distribution of men?  Not at all.  At a previous point in my life, I had the opportunity to become friends with a reformed crack dealer.  Most of the time, our converstions were pretty mundane, but occasionally he would indulge my curiosity about the workings of life in “the hood”.  One of the things that I found most interesting was that he was a virgin until after he had reformed, and met his wife to be.  I asked him if that was common (being a gun toting, crack dealing thug, and a virgin), and he said that it was far more common than one might expect.

Will “superbugs” kill people in the future?  I agree with you that this is will most likely occur.  But will there be any selection based on genetics?  I’d say less likely than ever before.  Access to treatment will be far more important than say during the Middle Ages, when effective treatment was hard to come by.  Treatment access will be less related, if related at all, to genetics than old time “fitness.”  And massive die outs will be less likely - the breakouts will be contained, via quarantine and treatment.  Random mutations will not lead to “evolution” if the selection is random, too.  And selection is getting more random all the time…

Dead wrong.  The rise of superbugs means that treatment is destined to become less important, as the treatment methods become increasingly useless.  As treatment is factored out of the equation, genetics play a greater role.

For true evolution to occur, there can’t just be more white noise in the genome - there must be sustained selection pressure that forces the gene pool to move in one direction or another.  Put another way, we may have outpaced the role of genetics in selection.  Alot of the factors you point out - pollution, global travel, poverty - are very real public health concerns.  But relative to historical norms, we now live in a world were these things fluctuate rapidly - too quick for the gradual, persistant process of evolution to allow us adapt to them, particularly when selection based on even these factors is at an all time low.

I disagree.  Things like global travel represent a fundamental shift in the way that humans live.  Unless you suppose that it is a fad that will go away soon?  There are many other similar changes that are highly unlikely to be reversed:

birth control
selective abortion
genetic histories for prospective parents
immunization
food and drug testing
increased literacy
etc.

What these things all have in common is that they represent a substantive change from what things were before, and a change that may be supplanted by new things, but is unlikely to be undone.  Furthermore, these changes all cary reproductive consequences.  One might suppose that things like immunization reprsent a decrease in selection pressure, but they would be wrong, at least in the theoretical sense.  In the pre-immunization days, certain genes (or lack thereof) carried a death sentence, but who knows what benefits they might also have confered?  For whatever diseases immunization might eliminate, there are (in theory) genetic pathways that become available which might not have been before.  Think about it.

-Matt

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Posted: 21 July 2005 04:11 AM   [ Ignore ]   [ # 23 ]  
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Psi -

I’m afraid this thread is devolving (NPI) into a flame war, which is not my intent.  There are too many true idiots out there (theChumpion comes to mind) for us to be arguing amongst ourselves.  And I never intended to put words into your mouth.  That said, here goes, once more into the breach…

You make an argument using the example of obesity.  It is reasonable, but pure conjecture, with a ton of holes.  There is NO PROOF that the genetics linked to obesity results in decreased reproductive fitness.  The age of death for the problems of the morbidly obese (heart attack, stroke, etc)  is well beyond the average reproductive age.  From the gene’s point of view, we are nothing but hosts; once the genes have been passed on, the don’t “care” if we live another 5 months or 50 years.

However, lets say, for the sake of arguement, a simple, straightforward gene that causes early, lethal obesity is discovered.  This hypothetical gene kills young people in their mid twentys, and has only been activated by “modern” life - fatty foods.  It was never a problem before.  Surely “evolution” will force this gene out of existance?  Not so fast - once we know about the gene, we can detect it.  Now, we can warn those with the gene to avoid fatty foods.  Now they grow up and have children, and pass the gene on.  And their children fly around the world and marry natives of a South Pacific island, mixing their genes together, etc, etc.

With regard to “superbugs”, I think you’ve been reading too many Robin Cook novels.  Take some of the emerging disease threats of recent years - SARS, West Nile, etc.  Are you telling me that the people who were exposed to these diseases did not benefit from medical treatment?  I’m afraid it is you who is, as you are fond of saying, “dead wrong.”  Even patients who get poly-resistant bacterial infections respond to supportive treatment, and modern medicine allows us to isolate them and prevent outbreaks of these diseases.  For all the hype of “flesh eating bacteria,” it has killed at most a handful of people, surely not enough to appreciably direct the evolution of the species.

I think my underlying problem with your conceptulization of evolution.  It is not a “rapid response” solution to challenges an organism faces.  While I agree that changes in the environment can certainly influence an organism’s evolution, for it to do so, it must be sustained and pervasive relative to the population to direct a change, and impact the selection of offspring.  Changes in a particular gene or allele’s frequency in the population do not equal “evolution.”  There also must be selective pressure.  If no genes are lost, then the gene pool may grow larger, but the center of the pool stays put.  Let’s say there is a genius gene that was previously a death sentence due to a lack of immunity (unlikely, but lets say…).  Now it is not a death sentence, and it will increase in the population.  There are a few more geniuses around.  We’ve evolved, right? Wrong, unless those genius genes carry some kind of sustained selective advantage, and increase in number each generation.  Otherwise, that gene will get thrown back in the pool with each go round.

Let me give you a concrete example.  Sickle cell anemia is as straightforward a genetic disease as you could ask for.  One copy of the sickler gene, and you have sickle trait (mild disease); two sickle genes, you have full blown SCA -  a painful, historically fatal condition, capable of killing before reproductive age.  So why does this gene persist in the population?  Eh, there’s the rub - the one copy people have an ADVANTAGE in facing malarial infection.  So, the number of carriesr of the trait in the population reaches an equilibrium based on the external selection pressure (malaria) and the inherent disadvantage of the gene (two copy offspring die).

Now along comes modern medicine.  Now we can treat sicklers, so they live and reproduce.  We can also treat malaria, so it is not as lethal a killer.  So what happens to the sickler gene?  Nothing.  It does not increase in frequency, but it also does not go away. There is no selection pressure now.  It rides along in the genetic stream, passing from generation to generation.

The difference between the above scenario and your hypothetical obesity one is that there are actual data to support the sickle cell story.  To conclude this now lengthy diatribe, I never said money is everything, or that global travel is a fad.  In fact, financial fitness and reproductive fitness are less linked than ever before in our species’ history, and that trend will continue.  And in fact it is because of the presence of global travel that intermixing of human populations has occured and will continue, and I don’t think the future face of humanity is likely to change much.

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Posted: 21 July 2005 09:39 AM   [ Ignore ]   [ # 24 ]  
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[quote author=“mhatter13”]I’m afraid this thread is devolving (NPI) into a flame war, which is not my intent.  There are too many true idiots out there (theChumpion comes to mind) for us to be arguing amongst ourselves.  And I never intended to put words into your mouth.  That said, here goes, once more into the breach…

Agreed, I don’t want this to develop into a flame war, and although you seriously irritated me with your ad hominem snipe about my educational and professional background, I respect your perspective.

You make an argument using the example of obesity.  It is reasonable, but pure conjecture, with a ton of holes.  There is NO PROOF that the genetics linked to obesity results in decreased reproductive fitness.  The age of death for the problems of the morbidly obese (heart attack, stroke, etc)  is well beyond the average reproductive age.  From the gene’s point of view, we are nothing but hosts; once the genes have been passed on, the don’t “care” if we live another 5 months or 50 years.

You are correct that there is no proof, but as you may remember, this discussion started with me attempting to conceptually demonstrate that evolution is likely going in, in humans, as we type, so to speak.  With the obese people, the second part of my example is as important as the first, which is that genes which alter the ability of a parent to care for and provide for their offspring are also worthy of consideration when it comes to assessing a particular genes fitness.  You make the point (rightly) that access to services (which is wealth linked) is important, but then you attempt to divorce it (wrongly, IMO) from genes.  I would say that it is highly likely that there are genes which have an adverse affect on wealth potential, which then likely bear a (subtle) reproductive fitness penalty.  The affects of such subtle pressure would take thousands of years to see visibly, but might be detectable by comprehensive genetic surveys looking for evidence of such drft (which was sort of my original thrust).

However, lets say, for the sake of arguement, a simple, straightforward gene that causes early, lethal obesity is discovered.  This hypothetical gene kills young people in their mid twentys, and has only been activated by “modern” life - fatty foods.  It was never a problem before.  Surely “evolution” will force this gene out of existance?  Not so fast - once we know about the gene, we can detect it.  Now, we can warn those with the gene to avoid fatty foods.  Now they grow up and have children, and pass the gene on.  And their children fly around the world and marry natives of a South Pacific island, mixing their genes together, etc, etc.

Fair enough, but I doubt that all such genetic conditions are so easily managed, and if it should be determined that there is a gene which codes for an abnormal desire for fatty food?  Then surely the two of them together represent a killer combo (and yes, now I am kidding a bit).

With regard to “superbugs”, I think you’ve been reading too many Robin Cook novels.  Take some of the emerging disease threats of recent years - SARS, West Nile, etc.  Are you telling me that the people who were exposed to these diseases did not benefit from medical treatment?  I’m afraid it is you who is, as you are fond of saying, “dead wrong.”  Even patients who get poly-resistant bacterial infections respond to supportive treatment, and modern medicine allows us to isolate them and prevent outbreaks of these diseases.  For all the hype of “flesh eating bacteria,” it has killed at most a handful of people, surely not enough to appreciably direct the evolution of the species.

The superbugs issue is more complicated. . .  You may be right, but I would counter to consider the following:

1. There are many bacterial infections currently being (easily) dealt with via antibiotics.

2. Hospitals are operating under increasing strain.

3. As more bacterial infections become progressively more antibiotic resistant, the strain on hospitals will increase, as conditions which were easily treated before require more treatment.

And so on.  Access to antibiotics has been fairly universal for much of the worlds population for many decades.  This has been because antibiotics are cheap and easy to administer.  The kinds of care required for someone with an antibiotic resistant strain are not so cheap or easy though, which may have additional side effects.  Just a thought.

I think my underlying problem with your conceptulization of evolution.  It is not a “rapid response” solution to challenges an organism faces.  While I agree that changes in the environment can certainly influence an organism’s evolution, for it to do so, it must be sustained and pervasive relative to the population to direct a change, and impact the selection of offspring.  Changes in a particular gene or allele’s frequency in the population do not equal “evolution.”  There also must be selective pressure.  If no genes are lost, then the gene pool may grow larger, but the center of the pool stays put.  Let’s say there is a genius gene that was previously a death sentence due to a lack of immunity (unlikely, but lets say…).  Now it is not a death sentence, and it will increase in the population.  There are a few more geniuses around.  We’ve evolved, right? Wrong, unless those genius genes carry some kind of sustained selective advantage, and increase in number each generation.  Otherwise, that gene will get thrown back in the pool with each go round.

I agree that evolution tends to work on a slow and steady timeframe, but there is still punctuated equilibrium.  My original example of the black plague in Europe comes to mind.  That disease single handedly shifted the center of the European gene pool.  There are doubtless other gene linked traits which will have a somewhat sudden and catastophic confrontation with a suddenly altered environmental condition in the future.

Again, it isn’t proof, but I am asking not for belief here, but an open mind.  Another way to look at this would be the following thought experiment:

Imagine, if you will, that the history of the last two thousand years had gone differently, and that people were still pre-industrial with a largely agrarian economy.

If you could sample the gene pools of both our world, and this (admittedly hypothetical) alternate reality, what would you expect to find?  They might be, on the whole, indistinguishable from each other.  However, they might have key discrepencies which would actually reflect the subtle differences in selection pressure between those two environments. 

Let me give you a concrete example.  Sickle cell anemia is as straightforward a genetic disease as you could ask for.  One copy of the sickler gene, and you have sickle trait (mild disease); two sickle genes, you have full blown SCA -  a painful, historically fatal condition, capable of killing before reproductive age.  So why does this gene persist in the population?  Eh, there’s the rub - the one copy people have an ADVANTAGE in facing malarial infection.  So, the number of carriesr of the trait in the population reaches an equilibrium based on the external selection pressure (malaria) and the inherent disadvantage of the gene (two copy offspring die).

I am well aware of sickle cell anemia.

Now along comes modern medicine.  Now we can treat sicklers, so they live and reproduce.  We can also treat malaria, so it is not as lethal a killer.  So what happens to the sickler gene?  Nothing.  It does not increase in frequency, but it also does not go away. There is no selection pressure now.  It rides along in the genetic stream, passing from generation to generation.

Maybe, but due the genetic screening, there is an increasing chance that prospective parents who each have one copy of the gene will decide not to have children.

There is actually a good place to examine how this sort of human directed behavior is influencing the gene pool.  As you may or may not know, there are many genetic diseases which are highly prevalent in people of Jewish descent.  Thanks to advances in molecular biology, many of these conditions are being stamped out, because prospective parents are getting screened.

Of course, you will probably note that the genes are still hanging around, and thus feel that no true shift of the genetic center has happened.

Perhaps we will just have to (amicably I hope) agree to disagree.

-Matt

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Posted: 21 July 2005 11:06 AM   [ Ignore ]   [ # 25 ]  
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Sorry about the apparent ad hominem attack - really not my intent; it was the result of the tonal deafness of cyberspace.  I actually was serious, and curious - the issue is controversial even amongst evolutionary biologists, many of whom would agree with you, I think, at least on some points.  As a biologist, I was just curious as to your background, thats all.

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Posted: 21 July 2005 12:20 PM   [ Ignore ]   [ # 26 ]  
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[quote author=“mhatter13”]Sorry about the apparent ad hominem attack - really not my intent; it was the result of the tonal deafness of cyberspace.  I actually was serious, and curious - the issue is controversial even amongst evolutionary biologists, many of whom would agree with you, I think, at least on some points.  As a biologist, I was just curious as to your background, thats all.

Water under the electronic bridge.  Misunderstandings aside, it is often helpful to understand where someone is coming from in order to fully appreciate the nuances of what it is that they have to say.

Apologies for snapping a bit more ferociously than may have been waranted.

-Matt

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Posted: 21 July 2005 01:19 PM   [ Ignore ]   [ # 27 ]  
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Could you two smart guys look at two other phenomena?

1.  Since we walked out of Africa about 50,000 years ago, we seperated into seperate gene pools.  Historically, war has been one of the major factors in mixing up those old pools, but now its just the way civilization is more mobil.  Do we gain any strength or lose any from mixing pools that have been seperated for thousands of years?

2.  I think the statistic is that 46% of German women 40 years old had no children, and its much the same for alot of the so called first world.
As women in countries get access to control of their lives, they now can choose when and if and how many children to have.  It would seem to me, the smarter, more capable and more educated the woman, the less likely she is to reproduce early and alot. 

Would you consider either of these social factors effects on evolution?

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Posted: 21 July 2005 01:42 PM   [ Ignore ]   [ # 28 ]  
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Iisbliss, I believe you have errored in your post. We did not “walk out of Africa.” Man was created in a place called the garden of Eden. And he did not just walk on his own. He recieved the breath of life from the creator.

Just bringing you up on the facts (through faith). grin

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Come to me, all you who are weary and burdened, and I will give you rest. Take my yoke upon you and learn from me, for I am gentle and humble in heart, and you will find rest for your souls. For my yoke is easy and my burden is light. Matt 11:28-29

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Posted: 21 July 2005 03:26 PM   [ Ignore ]   [ # 29 ]  
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Facts? Facts require proof do they not? Where is yours? You have a book, and possible more books that say this but there are also books that say the opposite. Show some actual proof.

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Posted: 21 July 2005 03:32 PM   [ Ignore ]   [ # 30 ]  
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[quote author=“Iisbliss”]Could you two smart guys look at two other phenomena?

1.  Since we walked out of Africa about 50,000 years ago, we seperated into seperate gene pools.  Historically, war has been one of the major factors in mixing up those old pools, but now its just the way civilization is more mobil.  Do we gain any strength or lose any from mixing pools that have been seperated for thousands of years?

2.  I think the statistic is that 46% of German women 40 years old had no children, and its much the same for alot of the so called first world.
As women in countries get access to control of their lives, they now can choose when and if and how many children to have.  It would seem to me, the smarter, more capable and more educated the woman, the less likely she is to reproduce early and alot. 

Would you consider either of these social factors effects on evolution?

Interesting points.

With regards to the first point:  There is a concept called hybrid vigor, which addresses this concept.  The idea is that smaller, seperate gene pools within the same species often have different genetic issues (and perhaps strengths), but since many of the genetic disadvantages that hang around are recesive, when parents from these different backgrounds produce offspring, they tend to not suffer from the genetic diseases of either background.

Does this apply to people?  It almost certainly does, at least to some degree.  There are several peoples who, either for geographic or ethnic reasons, have been fairly segmented, and have substantially higher chances of having certain genetic diseases.  If someone from one of these backgrounds were to have children with someone from a different background, the odds of their children having one of those genetic diseases would be reduced.

Whether or not this has an overall effect on our “strength” or “weakness” is trickier to say.  Ultimately, if I had to guess (and that is all it is), I would guess that the advent of genetic screening and selective parenting will eclipse mobility in terms of how it alters human genetics (especially regarding disease), which will make it hard to know what mobility would have done all on its own.

As for the second point:

The trend amongst women to have fewer children as their status improves is undeniable.  This has lead some people to speculate that this will lead to a “dumbing down” of the population, but I believe that belief springs from the false notion that the more “advanced” peoples of the world are somehow superior on a genetic level.

My guess, and again, this is only a guess, is that, as a result of globalization, rising standards of living will result in more women opting to wait longer to have children, and having fewer of them.

-Matt

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