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Author Topic:   Are mutations truly random or are they guided?
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


(1)
Message 7 of 134 (548565)
02-28-2010 8:18 AM
Reply to: Message 1 by herebedragons
02-27-2010 11:46 PM


Hi again herebedragons,
Just a small comment:
The DNA contains all necessary information for the growth and development of the organism. Look out over a cornfield and you will see that all the plants are about the same height, have developed in the same sequence and mature at about the same time. This is a highly regulated process. Even when hundreds of cell types are involved in an organism, they still manage to organize into tissues, organs and systems with incredible precision.
And yet no two plants are identical even though they come from highly controlled seed production in today's fields. You will find some "runts in the litter" that do not do as well in growth and production of corn (survival and reproduction), and you will find some that grow and produce more than the average ones.
Those differences are due to mutations. We can eliminate environmental effects on development when the whole field would experience the same effects, so we are left with differences in the DNA to produce the differences observed.
Enjoy.

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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This message is a reply to:
 Message 1 by herebedragons, posted 02-27-2010 11:46 PM herebedragons has not replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 65 of 134 (548786)
03-01-2010 8:21 PM
Reply to: Message 28 by Percy
03-01-2010 9:18 AM


unreal expectations based on false information
Hi Percy,
Given that we don't know everything and never will, there will always be questions for which we have few or no answers. Concerning examples of positive mutations in mammals, I'd be surprised if we know of very many.
Note that Bolder-dash is not concerned with real mutations at all. What he wants is evidence of single point mutations that form whole new features.
Message 24: Neither you, nor anyone else, can give any examples of positive random mutations cropping up spontaneously in animal populations, such that would develop into new, functioning systems or organs.
In other words the "hopeful monster" mutation misrepresentation used by those ignorant of real evolution.
(ibid): For a theory that depends ENTIRELY on a continuation of these type of developments happening in every animal population, your non-existence of actual examples of them is remarkable to say the least.
And ignorant of what the theory of evolution is really about. We saw this ignorance firmly adhered to in the previous threads, and a complete refusal to learn about reality, so I don't expect any real progress in understanding to be evidenced. Good luck.
Enjoy.

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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This message is a reply to:
 Message 28 by Percy, posted 03-01-2010 9:18 AM Percy has seen this message but not replied

Replies to this message:
 Message 68 by Bolder-dash, posted 03-02-2010 8:45 AM RAZD has replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 86 of 134 (548956)
03-02-2010 6:52 PM
Reply to: Message 68 by Bolder-dash
03-02-2010 8:45 AM


Re: unreal expectations based on false information
Hi Bader-dash
This is a good expalantion for why your side gets beat up so bad in live debates (see Meyer/Sternberg vs. Shermer/Prothero).
And also why your side got creamed at the Dover trial - we stick to facts rather than fantasy. Facts may seem boring, but the tend to be more substantial than fantasy in the long run. Interestingly, whenever the judgment on who "wins" is based on the relation to reality, science wins over fantasy every time.
It's also why your side cannot get traction on the concept that ID is science ... except among people who are ignorant of science.
It is YOUR side that says these random mutations are so numerous as to be able to explain the existence of all of life's complexities-yet you can show none.
This has been answered by others, but I'll bet you won't understand. The reason you are different from every other human on the planet is due to mutations.
So, the only hopeful monster in the room seems to be your theory, claiming for all its worth, a divine exclusivity on the facts-while providing no evidence whatsoever.
And yet, somehow, whenever an experiment is done to test the theory (the real one used by scientists), they end up with results that show that indeed evolution occurs and documents precisely the effects of evolution on the results.
Meanwhile the results based on creationism are ... still missing.
... we have witnessed in our lifetimes billions and billions of generations of bacteria-and not a single new complex system has seen to have been formed-nothing leading down the path of greater complex organisms.
Curiously, the real theory of evolution explains why simple prokaryotic bacteria still exist, including cyanobacteria very similar to the fossils of the first know life, from 3.5 billion years ago.
It explains it because complexity is not a goal of evolution.
Enjoy.

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 68 by Bolder-dash, posted 03-02-2010 8:45 AM Bolder-dash has replied

Replies to this message:
 Message 89 by Bolder-dash, posted 03-02-2010 9:34 PM RAZD has replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 107 of 134 (549083)
03-03-2010 9:47 PM
Reply to: Message 89 by Bolder-dash
03-02-2010 9:34 PM


Re: unreal expectations based on false information
Hi Balder-dash, still struggling with reality?
Note for herebedragons -- see ps at end
Hmm, they show evolution, by random mutations (you do mean evolution by random mutations, correct? Because certainly YOU would never post something off topic) occurring? Interesting.
By random mutation and genetic drift.
By random mutation and natural selection.
Evolution is the change in the proportion of hereditary traits in a breeding population from generation to generation in response to the opportunities of their ecology.
One of your problems is that you assume that your belief that evolution is wrong is true, and therefore that there cannot be evidence for anything based on evolution. Unfortunately, for you, starting with false assumptions leads to false conclusions.
You assumed that this evidence cannot be readily found.
Coyote gave you a link to a list of such experiments, but it appears that you have ignored it (or found it too dangerous to read?)
With google scholar {"random mutation" evolution} returns some 8,100 hits of journal articles about these two items.
One example comes from Coyote's link: https://myxo.css.msu.edu/ecoli/
Interesting study, over 20 years of accumulated evolution from a single source, shows a random beneficial mutation arising in one population that is based on a previous neutral mutation.
https://myxo.css.msu.edu/ecoli/overview.html
quote:
The inexorable rhythm of the project is as follows:
1. Every day, the cultures are propagated;
2. Every 75 days (500 generations), mixed-population samples are frozen away; and
3. Mean fitness, relative to the ancestor, is estimated using the mixed-population samples.
Pretty boring stuff eh?
https://myxo.css.msu.edu/...ate2008/citrateflasksphotos.html
quote:
Photograph of the long-term evolution experiment taken on 25 June 2008. Each flask harbors one of the 12 evolving populations. The photo was taken about 24 h after the cultures were serially transferred, hence they are at stationary phase. The populations grow in DM25 medium, which contains a relatively low glucose concentration so that the culture is not very turbid. However, one population, designated Ara-3, evolved to use the citrate that is also present in the medium. It has a much greater density of cells than the others, and it is therefore much more turbid, owing to the high concentration of citrate in the medium. (Below) A close-up view showing the Ara-3 population and two others. [Photos courtesy of Brian Baer and Neerja Hajela.]

Random mutation leads to new ability to use an additional source of nutrition, and this leads to increased growth and reproduction of the cells with the citrate mutation.
There's more, here's the peer reviewed journal published article abstract:
Just a moment...
quote:
Abstract
The role of historical contingency in evolution has been much debated, but rarely tested. Twelve initially identical populations of Escherichia coli were founded in 1988 to investigate this issue. They have since evolved in a glucose-limited medium that also contains citrate, which E. coli cannot use as a carbon source under oxic conditions. No population evolved the capacity to exploit citrate for >30,000 generations, although each population tested billions of mutations. A citrate-using (Cit+) variant finally evolved in one population by 31,500 generations, causing an increase in population size and diversity. The long-delayed and unique evolution of this function might indicate the involvement of some extremely rare mutation. Alternately, it may involve an ordinary mutation, but one whose physical occurrence or phenotypic expression is contingent on prior mutations in that population. We tested these hypotheses in experiments that replayed evolution from different points in that population's history. We observed no Cit+ mutants among 8.4 1012 ancestral cells, nor among 9 1012 cells from 60 clones sampled in the first 15,000 generations. However, we observed a significantly greater tendency for later clones to evolve Cit+, indicating that some potentiating mutation arose by 20,000 generations. This potentiating change increased the mutation rate to Cit+ but did not cause generalized hypermutability. Thus, the evolution of this phenotype was contingent on the particular history of that population. More generally, we suggest that historical contingency is especially important when it facilitates the evolution of key innovations that are not easily evolved by gradual, cumulative selection.
In other words, a neutral mutation arose somewhere between 15,000 and 20,000 generations that was needed as a scaffold for the later beneficial mutation.
That's not all:
https://myxo.css.msu.edu/ecoli/genomicsdat.html
quote:
Genome sequence of the ancestral strain, REL606, a derivative of E. coli B:
• Complete REL606 genome sequence deposited in GenBank
• First 2009 J Mol Bio paper describing historical derivation of E. coli B
• Second 2009 J Mol Bio paper presenting genome sequence of REL606
• Third 2009 J Mol Bio paper comparing genome sequences of REL606, another B derivative, and E. coli K-12
They have sequenced the DNA so they can determine where the mutations are for the neutral mutation building block and for the citrate metabolizing mutation.
Random mutation and genetic drift -- allows a neutral mutation to propagate in the population.
Random mutation and natural selection -- once a beneficial mutation occurs, here for citrate metabolizing, natural selection applies, and the cells with the beneficial mutation grow and reproduce at a much faster rate than the cells without the mutation, leading to a dominant population of cells with the mutation.
Evolution -- the change in the proportion of hereditary traits in a breeding population from generation to generation in response to the opportunities of their ecology.
Random mutation and genetic drift
Random mutation and natural selection

Evolution.
QED
There were other results of the study as well, one that showed slowing rates of adaptive mutations being fixed in the populations as they became more adapted to the ecology, then shifting to an increasing rates of neutral mutations as the ecology becomes more limiting to population growth from lack of nutritional resources for additional cells. It was one of these later neutral mutations that led to the rise of the beneficial mutation.
This shows the effect of random mutation and natural selection in a population with a dwindling resource/individual ecology, and the stress response to increase the rate of mutation when resources become limiting. Higher mutation rate leads to more neutral mutations and this leads to more opportunity for a beneficial mutation to arise.
Evolution is the change in the proportion of hereditary traits in a breeding population from generation to generation in response to the opportunities of their ecology.
Random mutation and natural selection
Random mutation and genetic drift

Evolution.
This is typical of other studies involving mutations and their effect on evolution: they show evolution occurring, that the proportion of hereditary traits in breeding populations from generation to generation changes in response to the opportunities provided by their ecology.
I believe I had seen here before where posters are cautioned by the moderator that if they are going to make wild claims, they must back them up with evidence or be punished.
So we see that "whenever an experiment is done to test the theory (the real one used by scientists), they end up with results that show that indeed evolution occurs and documents precisely the effects of evolution on the results" is not a "wild claim" but one based on a cornucopia of evidence.
You can, of course, actually attempt to falsify the claim by providing an example of an experiment run to test the theory of evolution that does not show that evolution occurs. Good luck with that. Given your response to Coyote's post, however, I expect you to continue to bluster and whine instead of actually doing anything.
.....Oh, wait, no sorry I am wrong, I have only seen where 'creationists' are cautioned on this website for making claims without reference, ...
Yes, everyone knows how much creationists like to be made into beleaguered martyrs, so we let them rattle on post after post regurgitating their institutionalized ignorance before asking them to behave like everyone else, and abide by the rules that everyone else abides by.
You poor little thing, being treated as an equal, instead of some awesome superior, must be quite a blow to the dominus ego eh? Such blatant heartless discrimination, oy, such a trial.
... I have never seen an evolutionist cautioned for anything of the sort.
Perhaps you have not seen evolutionists being cautioned to abide by the rules, because they already do, as a matter of intellectual honesty.
Reality is like that.
Enjoy.
ps - for herebedragons, and the question of whether mutations are random or directed,
Consider that if the mutations are directed in the instance cited above involving a neutral mutation followed by a beneficial mutation that allows the carriers to metabolize an additional nutrient, 11 of the 12 populations failed to be directed to do this, and in the one where this occurred it took over 15,000 generations to get around to the neutral mutation that enabled the beneficial mutation, and then another equally large number of generations to finally get to the goal mutation.
Statistically unsupportable compared to random mutation.
Edited by RAZD, : ps
Edited by RAZD, : ...

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 89 by Bolder-dash, posted 03-02-2010 9:34 PM Bolder-dash has not replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 108 of 134 (549095)
03-03-2010 11:35 PM
Reply to: Message 100 by herebedragons
03-03-2010 11:21 AM


Let's get back on track then, from cookbooks to neoLamarkianism ...
Hi again, herebedragons, welcome to the rats nest.
Message 101: Who are the creationists? How can you recognize them, ... I only saw one person arguing against advantageous mutations and I’m not sure whether he is a creationist or not. He just seems to like to derail the discussion and get the evolutionists all worked up.
Yes Bolder-dash is a creationist, and yes, that is one of his favored modus operandi. Another is to repeatedly complain about just about anything. It seems that many creationists use troll tactics because they don't have any real arguments other that denial and misinformation. The result, whether intentional or not, is frequent derailment of topics so that the issues get muddied if anyone else tries to learn anything.
Let’s try to get this discussion back on topic. ...So let’s get back to the discussion, please.
The purpose of this thread is to discuss the evidence regarding mutations and whether they are really random or whether they are directed and guided by the cell or the organism and influenced by the environment.
Perhaps not knowledge in the traditional sense, but the cell does contain a vast amount of information. Each individual cell has all the information needed to construct an entire organism from a single cell. This is remarkable in itself - that from one cell all the tissues, organ and systems of an organism can develop. I would say that the cell knows how to develop in to the mature organism. It does not leave development to chance (although clearly there are instances where things go wrong or develop incorrectly, but the cell is extremely accurate and in the grand scheme makes very, very few mistakes).
This is the sort of hand waving dismissal of cellular complexity that prompted me to write my OP the way I did. It goes far beyond simply biochemical reactions. As a most basic example, put glucose and oxygen together and what happens? Nothing. The reaction requires an input of energy from the cell in the form of ATP. The complexity of these reactions, interactions and cellular controls increases exponentially from there. One of the key points here is the cell must be living for most of the processes to occur.
This may not constitute conscious thought, nor require it, but it deserves more recognition than calling them simply biochemical reactions. Without considering the issue of mutations or evolution, have I made my point about cellular complexity? Or do we need to continue discussing it?
One of the problems with discussing cell complexity is what we mean by "complexity." Another is using the product of over 3.5 billion years, rather than the minimum amount of complexity required for life. Of course we do not know how simple an organism can be and still be a viable life form, but there are some prokaryotic cells with very little DNA compared to multicellular life forms. This comes at the abiogenesis question from the other side.
Likewise the "vast amount of information" in a modern cell is the product of 3.5 billion years of evolution, and does not constitute the minimum amount of information (and what is this "information"?) needed to form a living cell.
When you talk about the ability of a cell to reproduce a whole multicellular organism - " all the tissues, organ and systems" - you are really talking about a large accumulation of "things that work" and the elimination of a lot of "things that don't work" so that the processes that go on inside a cell are not just simply biochemical reactions but the ones that work. Selection does this.
Consider a cookbook: you don't need to know squat about chemistry and the way different products interact with the others, if you can read the recipe, measure the ingredients, and follow the correct cooking procedure you should get acceptable results. With a little variation in the ingredients you will get slightly different results, some better than others. Now annotate the recipe with what you did for the better results so you can replicate them next time. This is basically how the system works.
Following this process you can make any item in the cookbook. You are, however, limited from making anything that is not in the cookbook, so now consider how recipes are added to the cookbook. Different combinations of ingredients are tried, some work, sort-of, some work well, and some are disasters. The disasters are discarded and the "works well" and "sort-of works" recipes are added. By this process we can get from no recipes to a book with some fabulously delicious recipes and also with some recipes that are less than stellar.
The book has no intelligence, and it cannot tell whether one recipe is good or bad.
Consider that a cell is continually making every recipe in its"cookbook", modifying the recipes when improvements are discovered among the variations caused by errors in measurement or following the cooking procedure. There is no intelligence in the cookbook, only the accumulated "information" acquired by billions of years of trial and error of "things that work", including the ones that "work well" and the ones that "works sort of".
I have also noticed that there has been a resurrection of Lamarkism in recent years. I don’t think I would go to that extreme, but perhaps a form of it. I have also seen some instances of adaptation that , at least for me, call into question the randomness of those adaptations.
I'd be interested in those instances.
Lamarckism - Wikipedia
quote:
Forms of 'soft' or epigenetic inheritance within organisms have been suggested as neo-Lamarckian in nature by such scientists as Eva Jablonka and Marion J. Lamb. In addition to 'hard' or genetic inheritance, involving the duplication of genetic material and its segregation during meiosis, there are other hereditary elements that pass into the germ cells also. These include things like methylation patterns in DNA and chromatin marks, both of which regulate the activity of genes. These are considered "Lamarckian" in the sense that they are responsive to environmental stimuli and can differentially affect gene expression adaptively, with phenotypic results that can persist for many generations in certain organisms. Although the reality of epigenetic inheritance is not doubted (as countless experiments have validated it), its significance to the evolutionary process is uncertain. Most neo-Darwinians consider epigenetic inheritance mechanisms to be little more than a specialized form of phenotypic plasticity, with no potential to introduce evolutionary novelty into a species lineage.[16]
This seems to be more of interest in the "evo-devo" field than in general biology\evolution.
Lamarckism - Wikipedia
quote:
While Lamarckism has been discredited as an evolutionary influence for larger lifeforms, some scientists controversially argue that it can be observed among microorganisms.[17] Whether such mutations are directed or not also remains a point of contention.
In 1988, John Cairns at the Radcliffe Infirmary in Oxford, England, and a group of other scientists renewed the Lamarckian controversy (which by then had been a dead debate for many years).[18] The group took a mutated strain of E. coli that was unable to consume the sugar lactose and placed it in an environment where lactose was the only food source. They observed over time that mutations occurred within the colony at a rate that suggested the bacteria were overcoming their handicap by altering their own genes. Cairns, among others, dubbed the process adaptive mutation.
If bacteria that had overcome their own inability to consume lactose passed on this "learned" trait to future generations, it could be argued as a form of Lamarckism; though Cairns later chose to distance himself from such a position.[19] More typically, it might be viewed as a form of ontogenic evolution.
In microorganisms the details are confused by the possibility of horizontal gene transfer (or single cell sex), where a tidbit of DNA from one cell is injected into a neighbor cell. Thus a mutation in one cell that is beneficial can be spread to other neighboring cells rather than just to descendants.
And, of course, any survival or reproductive benefit that is due to a learned behavior (meme), rather than to a hereditary trait, is a acquired trait that is passed to those that learn it. Learned behavior of the organism, though, is not part of what you are considering as going on inside the cell, is it?
Enjoy.

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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This message is a reply to:
 Message 100 by herebedragons, posted 03-03-2010 11:21 AM herebedragons has not replied

Replies to this message:
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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 110 of 134 (549122)
03-04-2010 7:12 AM
Reply to: Message 109 by ZenMonkey
03-04-2010 1:15 AM


Re: unreal expectations based on false information
Don't feed the trollish behavior
Edited by RAZD, : .

This message is a reply to:
 Message 109 by ZenMonkey, posted 03-04-2010 1:15 AM ZenMonkey has not replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 124 of 134 (549326)
03-05-2010 8:18 PM
Reply to: Message 123 by Taq
03-05-2010 11:24 AM


Skin cells in the process of dying are shed continuously
Hi Taq, just a small additional point, one I'm sure you are aware of.
Tanning and pulmonary/vascular reconstruction are not due to mutations. A person does not acquire a mutation upon exposure to sunlight that then results in higher melanin production. And even if this occurred in somatic melanocytes it would NOT be inheritable. Tanning is an induced phenotype that does not require a single mutation.
You shed skin cells at a fairly rapid rate, such that in ~four weeks you have a completely new skin. Skin cells reproduce in lower layers by cell division (just like bacteria) and then migrate to the surface, dying in the process before being shed in a continuous process. There is no mechanism for anything in these outer skin layers to move back into the body.
Skin - Wikipedia
quote:
The epidermis contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis. The main type of cells which make up the epidermis are Merkel cells, keratinocytes, with melanocytes and Langerhans cells also present. The epidermis can be further subdivided into the following strata (beginning with the outermost layer): corneum, lucidum (only in palms of hands and bottoms of feet), granulosum, spinosum, basale. Cells are formed through mitosis at the basale layer. The daughter cells (see cell division) move up the strata changing shape and composition as they die due to isolation from their blood source. The cytoplasm is released and the protein keratin is inserted. They eventually reach the corneum and slough off (desquamation). This process is called keratinization and takes place within about 27 days.
Tanning results from the release of melanin into the surrounding skin cells from the melanocytes in response to sunlight.
Sun tanning - Wikipedia
quote:
Firstly, the UVA-radiation generates oxidative stress, which in turn oxidises pre-existing melanin. This leads to rapid darkening of already existing melanin. Secondly, there is an increased production of melanin (melanogenesis).[1] It is a reaction of the body to photodamage from UVB.[2] Melanogenesis leads to delayed tanning. It first becomes visible about 72 hours after exposure.[1] The tan that is created by an increased melanogenesis lasts much longer than the one that is caused by oxidation of existing melanin.
Darkening of the skin is caused by an increased release of the pigment melanin into the skin's cells after exposure to ultraviolet radiation. Melanin is produced by cells called melanocytes and protects the body from direct and indirect DNA damage absorbing an excess of solar radiation, which can otherwise be harmful.
Both the melanocytes and surrounding cells are part of the process of continual skin shedding. Any mutations that occur in the skin cell then are lost when the cells are shed, rather than being incorporated back into the organism.
Enjoy.

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 123 by Taq, posted 03-05-2010 11:24 AM Taq has not replied

Replies to this message:
 Message 125 by Coyote, posted 03-05-2010 9:12 PM RAZD has replied

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 126 of 134 (549332)
03-05-2010 9:51 PM
Reply to: Message 125 by Coyote
03-05-2010 9:12 PM


Re: Skin cells in the process of dying are shed continuously
Hi Coyote,
... but not every population has the ability to tan.
These differences are due to one or more mutations somewhere along the line during the migration from Africa to northern Europe.
The populations at the extremes, Africa and Scandinavia, do not tan. Those groups in the middle do. To me that suggests multiple mutations.
Like any trait, there are variations within the population, and in areas where tanning is beneficial the ability to tan can be selected over the tendency to burn, while in areas where tanning is not beneficial, loss of the ability to tan is not selected against and can come to predominate in the population.
This would show up in the skin cells via different patterns of cell distribution that occur during growth.
Epidermis - Wikipedia
quote:
The amount and distribution of melanin pigment in the epidermis is the main reason for variation in skin color in modern Homo sapiens. Melanin is found in the small melanosomes, particles formed in melanocytes from where they are transferred to the surrounding keratinocytes. The size, number, and arrangement of the melansomes varies between racial groups, but while the number of melanocytes can vary between different body regions, their numbers remain the same in individual body regions in all human beings. In white and oriental skin the melansomes are packed in "aggregates", but in black skin they are larger and distributed more evenly. The number of melansomes in the keratinocytes increases with UV radiation exposure, whilst their distribution remain largely unaffected. [6]
The distribution pattern is genetic.
Under exposure stress from UV the body reacts by processing more skin stem cells into melanocytes, and thus to produce more melanin in the (soon to be shed) skin. This is why you get deeper tan during the summer, while in the winter the process reverses.
The distribution doesn't change, so genetically you are limited by the distribution characteristic of your ethnic ecological genotype.
And you can cycle between deep summer tan and winter white without affecting your genetic makeup or even the ability to tan faster the next year.
Now if mutations were directed, or responsive to environmental factors, one would expect that there would be a noticeable improvement during a lifetime. One would expect the mutation rate to increase while experiencing the UV stress in the skin, and selection within the organism for increased protection provided by cell that lasted longer.
If mutations were random, then you would have no such effect, the pattern of tanning would be fixed in each individual.
Enjoy.
Edited by RAZD, : topic considerations

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 125 by Coyote, posted 03-05-2010 9:12 PM Coyote has replied

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