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chaloobi
SFN Regular
1620 Posts |
 Posted - 01/05/2005 : 20:02:36 [Permalink]
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quote:
Originally posted by filthy
You are right, of course. But I never said that any sort of evolutionary change would occur in an individual. We both know that that doesn't happen. A favorable mutation might show up, but it would be meaningless if it couldn't be absorbed into the population over generations.
Hence the need for natural selection....
quote:
What would happen to the immediate future generations if those medicines ceased to exist? Would they be more succeptable to disease due to no natural resistance? And how many generations would be required for a resistance to be built up?
I don't know for sure about this one but I've heard doctors argue that vaccines and anti-biotics didn't do nearly as much to reduce deaths by disease as a nutrionally proper diet, reasonable hygeine and overall sanitation did.
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-Chaloobi
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| Edited by - chaloobi on 01/05/2005 20:03:20 |
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beskeptigal
SFN Die Hard
USA
3834 Posts |
Posted - 01/06/2005 : 03:12:46 [Permalink]
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Dave has it right but perhaps I can put it another way that makes it easier for you to understand, Chaloobi.
First, evolution of rapidly reproducing organisms can be very fast. Evolution of humans is on the order of thousands of years. Don't expect to see big changes in your lifetime nor in much of written history either. I do think nutrition accounts for much of our size increase but there may have been a little selection influence there.
Second, and most important, survival of the fittest was a good model to start with but we know a lot more about evolutionary processes now and we know that model isn't exactly right.
Instead what you have is constant mixing of genes with two parents and subsequent off spring, and, a fairly constant rate of genetic mutation marching along.
Acting on those new gene combinations and mutations are many many 'selection pressures'. Selection pressures include mate selection, disease, pollution, climate, technology, food production, and so on.
Sometimes traits will be passed on that are neutral along with traits that selection pressures favored. These can spread far and wide among populations depending on the birth rate of a family line. We end up with an incredible amount of variability that actually ends up being a very highly survivable trait. (In addition there is built in redundancy so if a gene fails the paired gene is still there to function. But I'll leave that process out of the discussion for now.)
Let me give you an example. A gene has been found that has a single nucleic acid change in the DNA called a 'CCR5 deletion'. This mutation changes the protein wall of certain white blood cells but the cells still function normally. However, it turns out the change makes it much harder for the HIV virus to infect the person.
This mutation has been found in various amounts in various populations around the world. None of the persons with it come from areas of the world where HIV evolved. So what that tells us is this gene mutation is just part of the natural background variation of genes that randomly occur then get passed on either without much selection pressure or with a different selection pressure than the one which may select for the gene in the future. Then along comes a new viral disease, HIV, and these folks will already have some resistance to infection advantage in place.
Skin color is another example that illustrates evolution in progress. As humans migrated out of Africa, skin color eventually lightened to allow more Sun to make vitamin D. As humans migrated back from north to south in new continents skin color evolved back to dark skin to protect from damaging solar rays. This took thousands of years.
If we move to the equator from a temperate zone, our kids are not going to die if they have light skin and only survive if they have dark skin. But after thousands of years the slow erosion of light skinned persons from cancers could eventually lead to dark skinned offspring. On the other hand, with cancer treatment, sunscreen, clothes, hats, and knowledge of the hazard, evolution is likely to take a different course the next time. And since worldwide travel is so different than it was 200,000 years ago, the human race may end up with less variation in skin color worldwide.
So evolution in humans is relatively constant. Whether that evolution will result in different appearing human beings depends on multiple selection pressures. In any case, it takes thousands of years for big changes to occur. But genetic changes with less obvious results are occurring all the time. |
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filthy
SFN Die Hard
USA
14408 Posts |
Posted - 01/06/2005 : 05:12:32 [Permalink]
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quote:
Originally posted by chaloobi
quote:
Originally posted by filthy
Um, pretty broad statment, 'loobi. <snip>
By design. :)
quote:
<snip> Therefore, any mutation that might benefit us under other conditions simply never needed to be selected.
I couldn't disagree with you more. There's a lot more in the environment putting selective pressures on a species than climate. Indeed, climate is one of the characteristics of our environment that we can almost wholly adapt to with the use of our brains - via use of tools, clothing, etc.
quote:
As for recent evolution, we are taller, on the average. And this in just the last, couple of thousand years. An adult male at the time of Jesus might have been only 5'4'' to 5'6'' tall. This can also be seen in medevale suits of armor as well -- those guys were small! Few, modern men could fit into one.
Of course, while this increase in higth, largly selected for by our females who themselves became taller as a genetic result, is ok today, it could become a serious disadvantage in a changed environment.
As noted already, this is actually a nutrional thing. Our genes arn't changing for more height.
Less the snippage, my paragraph read thus:
"Ever since the last ice age, our enviornmental conditions have been all but ideal for our species (with minor variations here & there). Therefore, any mutation that might benefit us under other conditions simply never needed to be selected. It was to the species' advantage to stay pretty much as it was. If those conditions were to change, there can be little doubt that we would slowly change with them. Or not."
You will note that 'enviornmental conditions' mean more than just climate, although that is a large part of it. For example, if we'd had a major predator, our most successful populations would have developed (selected) to deal with it. But those predators vanished long ago, to our advantage.
The 'minor variations' mentioned is what gave us the great diversity found in out species; indeed, made us what we are -- bushmen and eskimos, rain forest indians and Austrailian aboriginies. And each of these races, as well as ourselves, became what it is due to natural selection for it's enviornment.
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"What luck for rulers that men do not think." -- Adolf Hitler (1889 - 1945)
"If only we could impeach on the basis of criminal stupidity, 90% of the Rethuglicans and half of the Democrats would be thrown out of office." ~~ P.Z. Myres
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Brother Boot Knife of Warm Humanitarianism,
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Siberia
SFN Addict
Brazil
2322 Posts |
Posted - 01/06/2005 : 05:58:02 [Permalink]
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I keep trying to understand the damned imperial system, and keep failing. However, I'm inclined to believe our population, as a whole, is smaller than North American population, as a whole. We can almost always tell a foreigner by height and skin color
But, just as an example on how diseases can impair development of height, I've the genes to be taller than I am, as well as the body proportions, so says my rheumathologist or whatever you spell that. Due to arthritis, however, I had my growth impaired, to a degree I'm short and stocky when I should be tall and slender |
"Why are you afraid of something you're not even sure exists?"
- The Kovenant, Via Negativa
"People who don't like their beliefs being laughed at shouldn't have such funny beliefs."
-- unknown
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 01/06/2005 : 07:58:42 [Permalink]
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Natural selection is a wide paintbrush and not the only driving force in evolution, genetics, mutation, breeding, and now with the huge potential of technology evolution is in strong effect, not to mention the majority of people in the world have no HMOs or florinated water.
Now if you want to clarify and say "Natural Selection" has been taken out of the human equation, fine. Just dont assume that evolution stops with natural selection. Because I know some penicillin resistant bacteria who want to be recognised.
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"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 01/06/2005 : 08:50:17 [Permalink]
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Chaloobi, please check out:At least for starters.
It's important to remember, when thinking about these things, that there are actually lots of tiny human sub-populations which have effectively isolated themselves. From the five tribes of less than 500 people on Andaman island in the news recently, all the way to zillions of American small towns where "the new guy" may have lived there for 50 years, the human species is not just one constantly-interbreeding population. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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chaloobi
SFN Regular
1620 Posts |
Posted - 01/06/2005 : 08:56:07 [Permalink]
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quote:
Originally posted by beskeptigal
Dave has it right but perhaps I can put it another way that makes it easier for you to understand, Chaloobi.
First, evolution of rapidly reproducing organisms can be very fast. Evolution of humans is on the order of thousands of years. Don't expect to see big changes in your lifetime nor in much of written history either. I do think nutrition accounts for much of our size increase but there may have been a little selection influence there.
Second, and most important, survival of the fittest was a good model to start with but we know a lot more about evolutionary processes now and we know that model isn't exactly right.
Instead what you have is constant mixing of genes with two parents and subsequent off spring, and, a fairly constant rate of genetic mutation marching along.
Acting on those new gene combinations and mutations are many many 'selection pressures'. Selection pressures include mate selection, disease, pollution, climate, technology, food production, and so on.
Sometimes traits will be passed on that are neutral along with traits that selection pressures favored. These can spread far and wide among populations depending on the birth rate of a family line. We end up with an incredible amount of variability that actually ends up being a very highly survivable trait. (In addition there is built in redundancy so if a gene fails the paired gene is still there to function. But I'll leave that process out of the discussion for now.)
Let me give you an example. A gene has been found that has a single nucleic acid change in the DNA called a 'CCR5 deletion'. This mutation changes the protein wall of certain white blood cells but the cells still function normally. However, it turns out the change makes it much harder for the HIV virus to infect the person.
This mutation has been found in various amounts in various populations around the world. None of the persons with it come from areas of the world where HIV evolved. So what that tells us is this gene mutation is just part of the natural background variation of genes that randomly occur then get passed on either without much selection pressure or with a different selection pressure than the one which may select for the gene in the future. Then along comes a new viral disease, HIV, and these folks will already have some resistance to infection advantage in place.
Skin color is another example that illustrates evolution in progress. As humans migrated out of Africa, skin color eventually lightened to allow more Sun to make vitamin D. As humans migrated back from north to south in new continents skin color evolved back to dark skin to protect from damaging solar rays. This took thousands of years.
If we move to the equator from a temperate zone, our kids are not going to die if they have light skin and only survive if they have dark skin. But after thousands of years the slow erosion of light skinned persons from cancers could eventually lead to dark skinned offspring. On the other hand, with cancer treatment, sunscreen, clothes, hats, and knowledge of the hazard, evolution is likely to take a different course the next time. And since worldwide travel is so different than it was 200,000 years ago, the human race may end up with less variation in skin color worldwide.
So evolution in humans is relatively constant. Whether that evolution will result in different appearing human beings depends on multiple selection pressures. In any case, it takes thousands of years for big changes to occur. But genetic changes with less obvious results are occurring all the time.
Actually, what you have said above, in bold, supports my argument with DaveW entirely. At least that sub-argument dealing with whether selection is necessary for evolution to take place. Some type of selection pressure must take place, whether directly on the gene in question or on one connected to it, giving it a 'free ride.' Otherwise a new trait cannot spread throughout the population.
So, back to my original contentious claim, IF natural selection has been eliminated, THEN evolution is not currently taking place. There most certainly are mutations taking place all the time. And certainly vast amounts of gene-pool mixing among diverse populations is occurring and producing never before seen traits, and so on. But UNLESS those traits are being selected for or against, there is no true evolution occurring.
Now, if you want to argue that there IS selection going on, which is the heart of my OP argument, then you have some basis for discussion. But if your argument is that evolution is still taking place despite there being no natural selection, then you are incorrect. Mutation is occurring. New traits are appearing. But evolution is not unless those traits are not being distributed to the wider population via selection.
Now I fully understand evolution is dependant on turnover of generations. And the longer it takes for a generation to mature and breed, the longer the time period for genetic change to spread through the population. And further, at best, if natural selection has been eliminated for humanity, then this condition has only been true for the last 100 years - four generations - at MOST. So the point is really moot. Our current state of affairs - completely unrstricted breeding - or in other words 'population explosion' - - has been in place far too short a time to even consider the question of evolutionary stagnation.
Now, to fully engage the real issue 'is natural selection currently taking place' I will now contradict my OP. I believe selection of various kinds IS now occurring in many parts of the world. Certainly any population with high infant mortality is experiencing selection. Any population where children do not have an almost guaranteed chance of reaching breeding age is also experiencing seleciton. And any place where the adult population is not routinely breeding at near 100% rates is also experiencing selection. The first two are present to varying degrees in Developing nations. The last is present in most Developed nations.
In these categories there are many complex sub-factors involved, such as AIDS, wealth, diet, water, and so on. For example, China has a 1 child policy, but urban populations are held to this rule to a much greater extent than rural. Further, the rule has led to the selecting of males over females, which I'm not sure how this might affect the local gene pool. Last, who really believes the nation's elite are being held to the 1 child rule? I'd guess that if you have enough influence or enough bribe money that you're able to have more than 1 child if you wish. Is any of this genetics related? I don't know.
So selection is most certainly occurring in various different ways around the world. Much of it is centered around wealth - national and personal - and social behavior. The interesting question is does any of that have anything to do with the human genome? Is there a gene that influences a decision that might lead you to get or avoid AIDS? Is there a gene that influences you to become affluent, which in developing nations likely increases your chances of breeding successfully and in developed nations decreases it? If the selection isn't based on some descreet genetic factor, then evolution is NOT occurring.
Conceivable, we could structure a society where anyone can breed if they want too, regardless of their genes. Indeed, in the US and the Wes |
-Chaloobi
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chaloobi
SFN Regular
1620 Posts |
Posted - 01/06/2005 : 09:03:32 [Permalink]
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quote:
Originally posted by Dave W.
Chaloobi, please check out:At least for starters.
It's important to remember, when thinking about these things, that there are actually lots of tiny human sub-populations which have effectively isolated themselves. From the five tribes of less than 500 people on Andaman island in the news recently, all the way to zillions of American small towns where "the new guy" may have lived there for 50 years, the human species is not just one constantly-interbreeding population.
I agree with you entirely. Where I was disagreeing with you was your contention that selection of some kind, natural or otherwise (if you want to insist that human activity is not 'natural' activity, an issue of definition which I don't happen to subscribe to), is not necessary for evolution to take place. I stand firmly in saying that if SELECTION is not occurring, EVOLUTION is not occurring. But of course in all the little sub-populations and sub-groups from regional to national to local and so on there's all sorts of different conditions in place. And yes, selection in many of these sub-groups is almost certainly taking place. |
-Chaloobi
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 01/06/2005 : 09:35:50 [Permalink]
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| Crap, Chaloobi, did you read the links I gave you? Genetic drift and gene flow can both act upon genes which are selectively neutral, thus changing the proportion of genes in the population as a whole. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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chaloobi
SFN Regular
1620 Posts |
Posted - 01/06/2005 : 09:42:39 [Permalink]
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quote:
Originally posted by Dave W.
Crap, Chaloobi, did you read the links I gave you? Genetic drift and gene flow can both act upon genes which are selectively neutral, thus changing the proportion of genes in the population as a whole.
No. <sheepish> I'll look at them and get back to you. |
-Chaloobi
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 01/06/2005 : 10:20:03 [Permalink]
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| And evolution is strictly defined as being a change in the proportion of genes in a population over time. If the world is 1.00000% redheads today, and 1.00001% redheads tomorrow (due to more redheads being born than dying overnight), then evolution has occured. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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chaloobi
SFN Regular
1620 Posts |
Posted - 01/06/2005 : 12:15:25 [Permalink]
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quote:
Originally posted by Dave W.
Crap, Chaloobi, did you read the links I gave you? Genetic drift and gene flow can both act upon genes which are selectively neutral, thus changing the proportion of genes in the population as a whole.
Alright, I read the first two. Regarding genetic drift, there are a few things to say with respect to humanity as we currently know it:
1. The almost universal cultural prohibitions against in-breeding work strongly against it. (Except in the hills of Kentucky) So genetic drift only occurs when the population has no other choice.
2. Humanity's burgeoning population and world-straddling mobility has all but elminated isolated populations, almost eliminating the situations where inbreeding becomes a necessity. Yes, you mentioned a few exceptions making your point technically correct, but is a tribe of 100 folks on some isolated island meaningful in the sea of 6 billion humans? Probably in the longer term, if they survived in their isolation.
I would guess that genetic drift is currently even less a factor in human evolution than natural selection, for the two reasons cited above. It can be speculated that declining human populations in the West might actually result in regions where genetic drift becomes a more significant factor. I doubt it though. Really wierd things would have to happen to bring that about. Wierder than mail-order brides to be sure. |
-Chaloobi
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 01/06/2005 : 13:03:10 [Permalink]
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The "inbreeding" stuff is important relative to the "founder effect," but genetic drift continues in larger populations (and their smaller sub-populations). Your guess is not compelling at all when there is a current and on-going debate amongst evolutionary biologists over which (selection or drift) is the more important evolutionary mechanism.
Two examples of genes which may be undergoing drift would be those responsible for psoriasis, and those responsible for breast cancer. These genes experience little, if any, selection pressure, as reproduction has often occured by the time the diseases become sypmtomatic. While in industrialized countries, psoriasis may be undergoing sexual selection out of the gene pool (as people are waiting longer to have kids, the average age of psoriasis onset is 28), the same doesn't hold true for undeveloped countries, nor does it hold true for breast cancer. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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chaloobi
SFN Regular
1620 Posts |
Posted - 01/06/2005 : 13:16:59 [Permalink]
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quote:
Originally posted by Dave W.
The "inbreeding" stuff is important relative to the "founder effect," but genetic drift continues in larger populations (and their smaller sub-populations). Your guess is not compelling at all when there is a current and on-going debate amongst evolutionary biologists over which (selection or drift) is the more important evolutionary mechanism.
Two examples of genes which may be undergoing drift would be those responsible for psoriasis, and those responsible for breast cancer. These genes experience little, if any, selection pressure, as reproduction has often occured by the time the diseases become sypmtomatic. While in industrialized countries, psoriasis may be undergoing sexual selection out of the gene pool (as people are waiting longer to have kids, the average age of psoriasis onset is 28), the same doesn't hold true for undeveloped countries, nor does it hold true for breast cancer.
Actually, the inbreeding quote goes like this:
quote:
"The process of genetic drift should sound familiar. It is, in fact, another way of looking at the inbreeding effect in small populations ... Whether regarded as inbreeding or as random sampling of genes, the effect is the same. Populations do not exactly reproduce their genetic constitutions; there is a random component of gene-frequency change." (Suzuki et al. op. cit.)
Yes it is part of the block quote referring to the founder effect, but it's clearly referring to all of genetic drift. And if you understand that genetic drift only occurs in small, reproductively isolated populations, you see that it is inbreeding. It doesn't matter how the population got small and isolated, colonization or cataclysm, either way the result is the same - inbreeding. I believe you're jumping the gun with your dismissal of my guess as non-compelling.  |
-Chaloobi
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| Edited by - chaloobi on 01/06/2005 13:18:30 |
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 01/06/2005 : 14:20:46 [Permalink]
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quote:
Originally posted by chaloobi
Yes it is part of the block quote referring to the founder effect, but it's clearly referring to all of genetic drift. And if you understand that genetic drift only occurs in small, reproductively isolated populations, you see that it is inbreeding. It doesn't matter how the population got small and isolated, colonization or cataclysm, either way the result is the same - inbreeding. I believe you're jumping the gun with your dismissal of my guess as non-compelling.
Your interpretation of Suzuki's comments about the founder effect dismiss his other comments (also quoted in the same article) about genetic drift in genral, which point out that all populations are finite, and in any finite population with a small reproductive rate, any selectively-neutral trait which makes an appearance will randomly drift either to the point where every individual carries it, or none do.
"[A]nother way of looking at" does not mean "exactly the same thing as." The founder effect is simply a crystal-clear example of genetic drift in action. Besides, inbreeding is the only thing possible when looking at the entire human population of the Earth (are there humans on another planet to breed with?).
Genetic drift in action: at some point in the history of Homo sapiens, there must have been a "first redhead." That trait, while still present in a minority of the world's population, is not gone, and undergoes only a small amount of sexual or natural selection. That redheadedness is associated with Ireland strongly suggests its appearance was rather recent, too. And whether redheadedness is rising or falling in percentage within the overall human population, it cannot remain at precisely the same proportion each and every generation (there don't exist fractions of a human). Evolution is occuring in humans, as we speak. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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