Posted on 02/28/2011 12:05:32 PM PST by SeekAndFind
Variations in skin color provide one of the best examples of evolution by natural selection acting on the human body and should be used to teach evolution in schools, according to a Penn State anthropologist.
"There is an inherent level of interest in skin color and for teachers, that is a great bonus -- kids want to know," said Nina Jablonski, professor and head, Department of Anthropology, Penn State. "The mechanism of evolution can be completely understood from skin color."
Scientists have understood for years that evolutionary selection of skin pigmentation was caused by the sun. As human ancestors gradually lost their pelts to allow evaporative cooling through sweating, their naked skin was directly exposed to sunlight. In the tropics, natural selection created darkly pigmented individuals to protect against the sun.
Ultraviolet B radiation produces vitamin D in human skin, but can destroy folate. Folate is important for the rapid growth of cells, especially during pregnancy, when its deficiency can cause neural tube defects. Destruction of folate and deficiencies in vitamin D are evolutionary factors because folate-deficient mothers produce fewer children who survive, and vitamin D-deficient women are less fertile than healthy women.
Dark skin pigmentation in the tropics protects people from folate destruction, allowing normal reproduction. However, because levels of ultraviolet B are high year round, the body can still produce sufficient vitamin D. As humans moved out of Africa, they moved into the subtropics and eventually inhabited areas up to the Arctic Circle. North or south of 46 degrees latitude -- Canada, Russia, Scandinavia, Western Europe and Mongolia -- dark-skinned people could not produce enough vitamin D, while lighter-skinned people could and thrived. Natural selection of light skin occurred.
The differences between light-skinned and dark-skinned people are more interesting than studying changes in the wing color of moths or, the most commonly used evolutionary example, bacterial colonies, according to Jablonski. Adaptation to the environment through evolutionary change becomes even more interesting when looking at the mechanism of tanning.
"In the middle latitudes tanning evolved multiple times as a mechanism to partly protect humans from harmful effect of the sun," Jablonski told attendees at the annual meeting of the American Association for the Advancement of Science today (Feb. 20) in Washington, D.C.
Tanning evolved for humans so that when ultraviolet B radiation increases in early spring, the skin gradually darkens. As the sun becomes stronger, the tan deepens. During the winter, as ultraviolet B wanes, so does the tan, allowing appropriate protection against folate destruction but sufficient vitamin D production. Tanning evolved in North Africa, South America, the Mediterranean and most of China.
Natural variation in skin color due to natural selection can be seen in nearly every classroom in the U.S. because humans now move around the globe far faster than evolution can adjust for the sun. The idea that variation in skin color is due to where someone's ancestors originated and how strong the sun was in those locations is inherently interesting, Jablonski noted.
"People are really socially aware of skin color, intensely self-conscious about it," she said. "The nice thing about skin color is that we can teach the principles of evolution using an example on our own bodies and relieve a lot of social stress about personal skin color at the same time."
Jablonski noted that the ability to tan developed in a wide variety of peoples and while the outcome, tanablity, is the same, the underlying genetic mechanisms are not necessarily identical. She also noted that depigmentated skin also developed at least three times through different genetic mechanisms. Students who never tan, will also understand why they do not and that they never will.
Provided by Pennsylvania State University
When the antibiotic is present the proteins have better function than those without the mutation.
That is what the mutation does, allows it to work in the presence of the antibiotic.
Without the antibiotic the bacteria is now under selective pressure to have the gene for that protein mutated back to the ‘default’/wild type.
That is why bacteria express error prone DNA polymerase during stress.
When subjected to the antibiotic it makes the mutation more likely. When the antibiotic is gone it makes back mutation favored.
Without teaching evolution how is anyone going to explain the existence and controlled expression of error prone DNA polymerase?
I mean if your model of life involves an ‘integrity of the genome’ and things NOT changing: how to explain why bacteria have a gene that deliberately introduces errors in DNA replication during stress?
The Earth goes around the Sun, but without explaining Gravity - knowing that is just an isolated fact that doesn't make any sense out of a cohesive whole.
Interesting quote mining. Do you believe that Richard Dawkins advocates the measures described in a century-old textbook?
“Where are “we” going in evolution? Nowhere fast, as we are a very homologous species with worldwide distribution and reproductive isolation is unlikely.”
What will be the next trans-human species? What will be the next bacterial species? Cannot be predicted. That’s why the comparison of gravity/evolution being both predictive is a little hollow, IMO.
“My prediction is that the petri dish subjected to heat stress will develop as a heat resistant strain of the bacteria, that the one subjected to cold will develop as a cold resistant bacteria, etc, etc.”
Understood. Do you have a prediction of what environmental stress you would have to impose to produce a multi-cellular organism evolved from the bacteria? Do we even know what mutations would have to occur to evolve from single to multi cellular.
Thanks for the reply.
There is no reason for life to ‘want’ to exist from the very beginning… But yet here we are… Human consciousness ultimately from mindlessness? No design?
It's not "gymnastics," it's merely a statement of scientific fact, and you apparently find it uncomfortable.
Are you attempting to imply that human management and utilization of technology somehow works to support the view that the range and complexity of biological systems are the product of intelligent design?
Not necessarily; however, it is a fact that humans can, and do, practice intelligent design on biological processes. And you've acknowledged the point -- and now you are attempting to shift the argument to one of degree. But the fact remains: you've acknowledged the fundamental point.
Your (and the NAS's, apparently) assertion that intelligent design is "not scientific," is demonstrably false. The rest, as they say, is merely haggling about the price.
You can make of that what you will -- but facts are facts, and a truly scientific approach to the question would force you to abandon that particular line of argument.
We know what genes are common to both one cellular life and those that are common only to multi-cellular life; and those common to both. Thus we gain an understanding for what genes are necessary, sufficient, or beneficial in a multi-cellular context.
All the machinery for cellular self destruction is absent in one celled organisms - yet every multicellular creature has them. They are the genes that are most commonly mutated in cancer.
So how would one explain why bacteria would have error prone DNA polymerase and why would it be expressed during stress without reference to natural selection of variation to derive adaptive responses?
As impossible as explaining how the Earth orbits the Sun without reference to Gravity.
RE: Wrong
That remains to be seen. Just because you say so does not make it so.
You ASSUME that something is true, and then on that basis extrapolate it to what you observe.
Of course I am open to the fact that you might be right, but you might also be wrong.
My point is this -— YOU DON’T HAVE TO APPEAL TO DARWINIAN EVOLUTION TO UNDERSTAND ANTIBIOTIC RESISTANCE, MUCH LESS HOW THE PLANETS MOVE.
What yo are doing is recognize that the resistance is already present in the bacterial population and then claim that selection for resistant bacteria in a population is direct evidence for Darwinian evolution.
Selecting for something that is already present does not necessarily provide support for the information-gaining change required for evolution.
Students are left with a confused understanding of evolution and are expected to equate observed changes in bacteria with the conversion of one kind into another.
One can still OBSERVE antibiotic resistance without appealing to either ID, creation or Darwinian Evolution.
For example, if I take a single bacteria of known genetics (because I sequenced it), and subject it to antibiotics - the antibiotic resistant strain will have a CHANGE in the genetics (I know because I sequenced it). What those changes consist of is then studied. But they didn't exist within the population - they were created through changes in the DNA - some of them no doubt through expression of error prone DNA polymerase.
Your explanation fails to account for the above scenario.
Willing to try for a different explanation? The “it was already there” explanation is absolutely incorrect.
And you don’t seem to understand this -— your explanation is just one of the many possible ways of looking at antibiotic resistance.
In fact it can be argued that much of the antibiotic resistance seen “evolving” in bacteria is not due to natural selection acting on genetic mutations, the neo-Darwinian method, but rather technology sharing.
I am not saying that this is the right explanation, simply that we should not shut ourselves out from such possible explanations.
Genes for resistance already exist in plasmids (round segments of DNA) that get passed around from one species of bacterium to another. By means of conjugation, bacteria share PRE-EXISTING genetic information. Those with antibiotic resistance due to mutations have lost genetic information that makes them less fit in the wild.
For instance, a receptor on the cell surface may get damaged by a mutation, prohibiting the antibiotic from entering. But this same mutational damage prevents needed substances from entering, making the bacterium defective. It might outcompete its un-mutated brethren in the artificial world of the hospital, but would most likely lose in the outside world.
A paper in the Nov. 28 issue of Science1 seems to confirm this.
Weigel et al. analyzed the genes of the well-known example of Staphylococcus areus resistance to vancomycin, and concluded it was conferred via conjugation of a plasmid containing the resistance gene.
See here :
Genetic Analysis of a High-Level Vancomycin-Resistant Isolate of Staphylococcus aureus
Weigel, et al.
Science 28 November 2003: 1569-1571.
DOI:10.1126/science.1090956
http://www.sciencemag.org/content/302/5650/1569.full
I am not saying that your explanation is wrong. I am saying that IT IS NOT NECESSARY to insist that Darwinian mechanisms are the ONLY EXPLANATION for what we observe.
That’s what I was saying to the other poster regarding education.
Is there a case where the penicillinase enzyme was observed to evolve in a population where it did not already exist?
There is a reason why we look for novel antibiotics - because there is no preexisting resistance to them.
A dozen years after the introduction of an antibiotic, and suddenly resistance is there, and passed around on plasmids, that without the presence and use of the antibiotic would be selected against until it would again disappear from existence - as you point out - it would most likely lose it in the “outside world” where there was no use of antibiotics.
Thus - where did the antibiotic resistance come from originally?
It is like the nylonase gene. Before there was nylon there was no ‘pay off’ to mutating an esterase gene to digest nylon. Without nylon the plasmid would rapidly cease to exist in the “outside world”. But outside a nylon production plant - now there is nylonase - an enzyme for digesting a synthetic compound that humans invented.
How do you explain THAT without reference to evolution?
How do you explain why bacteria have error prone DNA polymerase? Why would it be expressed in times of stress?
The basic structure itself capable of breaking down Penicillin like compounds is already present - but in penicillin susceptible bacteria the antibiotic is not a good substrate for the enzyme and it is not produced in sufficient quantity.
Again, you are insisting on one possible explanation for an observation as THE correct explanation.
Antibiotic resistance can also be looked at as just variation within the species of bacterium. I don’t see why this is invalid at all.
The bacteria may be losing information, not evolving into something more advanced. Consider how a man who loses his arm becomes immune to being handcuffed. Evolution is given far too much credit for helping bacteria evade the handcuffs. The bacteria are still bacteria, the same species of bacteria, after millions of generations. What’s evolution got to do with it?
This could be microevolution at best. Since the pathogens are most likely losing information, this is irrelevant to Darwinian evolution: i.e., the de novo emergence of new functional information.
What if all the information for antibiotic resistance, however, already exists in a library from which bacteria can find it? We cannot exclude such possibilities at all.
That seems to be the implication of a study by D’Carlo et al. in Science.
A Canadian biochemical research team decided to survey the techniques of antibiotic resistance already present in soil bacteria. They were astonished. Every antimicrobial medicine, including some only recently developed, had a defensive weapon ready for it:
This study provides an analysis of the antibiotic resistance potential of soil microorganisms. The frequency of high-level resistance seen in the study to antibiotics that have for decades served as gold-standard treatments, as well as those only recently approved for human use, is remarkable. No class of antibiotic was spared with respect to bacterial target or natural or synthetic origin. Although this study does not provide evidence for the direct transfer of resistance elements from the soil resistome to pathogenic bacteria, it identifies a previously underappreciated density and concentration of environmental antibiotic resistance.
See here :
D’Costa et al., “Sampling the Antibiotic Resistome,” Science, 20 January 2006: Vol. 311. no. 5759, pp. 374 - 377, DOI: 10.1126/science.1120800.
http://www.sciencemag.org/content/311/5759/374.full
Here’s another
Alexander Tomasz, “Weapons of Microbial Drug Resistance Abound in Soil Flora,” Science, 20 January 2006: Vol. 311. no. 5759, pp. 342 - 343, DOI: 10.1126/science.1123982.
http://www.sciencemag.org/content/311/5759/342.full
Note that these papers DO NOT ruled out that the resistance mechanisms have always been present in the gene pool.
If so, then the claim that bacteria “evolve” resistance to antibiotics is negated. Bacteria may simply find access to an existing library of information, a “resistome” that, coupled with a packaging and delivery mechanism (plasmids and transposons), confers the resistance that previously appeared to evolve out of thin air.
Notice that the resistance conferred by mutations harms the organism. The case cited by Tomasz reduced the fitness of the organism by weakening its cell wall. Mutationally-gained resistance is like the illustration Lee Spetner gave: cutting off a man’s arms makes him resistant to handcuffs. In a population of prisoners being handcuffed, this person would be the fittest, but only in a specific environment and at the cost of overall fitness. In the wild, he would be at a disadvantage. The kind of resistance conferred by specialized enzymes able to disable the agent, however, require specific genetic information that appears designed.
Too little is known at this point, but these articles uncover the possibility that genetic information that confers antibiotic resistance is already present in the environmental resistome. If so, this undermines a commonly-used evidence for evolution.
But my point still stands — YOU DO NOT NEED TO APPEAL TO EVOLUTION, ID or ANY THEORY OF ORIGINS to UNDERSTAND the mechanism behind antibiotic resistance. That was my point in my exchange with another poster (before you cut in our exchange ).
How do you explain error prone DNA polymerase?
It may well be that in mutating it “loses information” - or loses functionality compared to the wild type when the antibiotic is NOT present. But it can also “gain information” by mutating back to the wildtype, and backmutations would be favored by selective pressure as long as the antibiotic wasn't present.
Evolution explains it. That is what it has to do with it.
You can call it micro evolution if you want to.
How else are you going to explain it?
What do you think error prone DNA polymerase exists for, why would it be expressed during stress?
One need not think evolution is a “theory of origins” any more than gravity is a “theory of origins” that makes the creation of the Earth and the Sun something understandable and predictable and applicable to what we observe elsewhere instead of an act of supernatural instantaneous creation.
It explains what has gone of from that time, from wherever you care to start it, from now, it explains what will happen and why people use error prone PCR and selection to create enzymes for industrial use. Because random variation and stringent selection can have dramatic novel results - even if you want to insist the results were somehow already there. They were - in this instance - NOT!
How do you explain skin color differences again?
How did every species of beetle fit on a boat of known dimensions that is far too small to contain them all? Or is there beetle speciation? How do you explain beetle speciation?
It wasn’t ‘already there’.
http://www.newscientist.com/article/dn14094-bacteria-make-major-evolutionary-shift-in-the-lab.html
A major evolutionary innovation has unfurled right in front of researchers’ eyes. It’s the first time evolution has been caught in the act of making such a rare and complex new trait.
And because the species in question is a bacterium, scientists have been able to replay history to show how this evolutionary novelty grew from the accumulation of unpredictable, chance events.
Twenty years ago, evolutionary biologist Richard Lenski of Michigan State University in East Lansing, US, took a single Escherichia coli bacterium and used its descendants to found 12 laboratory populations.
The 12 have been growing ever since, gradually accumulating mutations and evolving for more than 44,000 generations, while Lenski watches what happens.
1959 We were smart, we developed a drug that doesn’t bind to penicillinase –
Methicillin!
1961 first isolates of Methicillin-resistant Staph aureus found
soon thereafter, loads of new drugs (and the cycle repeats)
gentamicin – an aminoglycoside – made by another bacterium, discoved by a Chinese
biologist, Yue Wang, messes with the bacterial ribosome
vancomycin – a glycopeptide – was discovered in the soil in Borneo – inhibits
incorporation of some peptide units into the peptidogycan matrix of cell wall
more and more
each discovery is great, but the bacteria have already have tools to fight
gentamicin, the drug that interferes with bacterial ribosome
soon after the commercial use of gentamicin,
we saw bacteria that have
- enzymes to modify the drug
- mutations in the bacterial ribosome
- active pumping of the drug out of the bacterial cell
vancomycin, the drug that inhibits building of peptidoglycan matrix
soon after the commercial use of vancomycin,
we saw bacteria that have
- alternate peptidoglycan that vanco wont bind
For awhile we were making loads of new drugs to run ahead of resistance, but soon we
realized we needed to understand the way this resistance works.
Tying this back to genetics….
Key Points to Understand about how resistance happens
Bacteria have been around a long time
Bacteria mutate spontaneously
Bacteria share genetic material
Bacteria compete for niches
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Selection pressure leads to bacteria significantly different from past types
Maybe the curly hair was cooler in the hot, sunny climates, and dried faster when wet?
Similarly, the naturalist believes that beneath every natural phenomenon there exists yet another natural phenomenon. If explanation by reference to an endless stack of large turtles is silly, then an explanation by reference to an endless stack of natural phenomena would be equally so. The naturalist's answer for the origin of life, therefore, is some natural phenomenon. (Which one is not particularly relevant.) When you ask them how that natural phenomenon came to be, their response boils down to: "It's natural phenomena all the way down!"Selection pressure leads to bacteria significantly different from past types
-Pete Chadwell
We hold no truths to be self-evident, that all (men) are evolved based on chance, that they are endowed by a mindless chemical process from a mindless universal algorithm with uncertain unalienable illusions that among these are a delusion of life, and the pursuit of happenstance. That to secure these illusions, governments are instituted among the chemical processes (called men), deriving their just powers from the happenstance of the governed.
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