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
“What is going to STOP this “descent with modification” such that over six million years a 2% genetic and 6% genomic DNA difference accumulate in separate populations?”
Well, it has never been observed. And seems most implausible.
2% and 6% is an incredibly wide chasm to breech in 6 million years. How many sequential beneficial mutations would that take? And each mutation would have to be so favorable as to be necessary for robustness, or impart some great advantage, in order for that mutation to predominate through the species.
Mutation/selection/descent has never been observed to any appreciable extent. An evolutionist sees fin, then sees leg, and “assumes” that you can get from one to the other by mutation and selection.
Can you give one example of a series of 5 sequential mutations, each one imparting an extraordinary robustness that the creature’s siblings and cousins did not experience, that result in survival or some great advantage? What about 4? What about 3? Bacterial resistance, and even metabolizing nylon are really biochemically trivial – a broken gene that just happened to yield resistance. Like the refuse washing down the flooded river might hit a snag in the river, begin to accumulate, and choke off flow downstream, and “build” a dam – but hardly a mechanism to account for an elaborate and exquisite dam with controlled gates and water flow, a secure crossing, generators, etc. And even such a dam does not begin to measure up to the processes and order of a living cell.
No, mutation and selection is a very poor mechanism for building complex biological systems. So poor as to be quite unbelievable to many who ponder such things.
A chimpanzee is already a complex biological system.
A 2% and 6% accumulation of difference is EASY to accomplish in 6 million years in two separate populations - that is a 1% change in genetic DNA and a 3% change in genomic DNA per population in six million years - what is going to PREVENT this change from accumulating?
DNA cannot be perfectly replicated. Assuming a generation time of 20 years, that is a 1% genetic DNA change in 300,000 generations or a 99.99967% fidelity rate in copying DNA.
If you think that amount if change is a “wide chasm to breech” you are only revealing that you know absolutely nothing about the subject.
Sorry, AMD, information in any car design was intelligently programmed. Same with every cell and organism. I’d like to have hearing as keen as a dog’s. Should be simple enough, except that humans are not *designed* with such capacity. Where does the information emanate which produces a hearing-capable organism in the first place?
You may believe what you wish, but until you can explain the answer to questions such as this and millions of others, skepticism of naturalism remains prevalent, AND totally rational. Bob
Beautifully stated! Bob
But there IS a natural explanation - a scientific explanation.
So far only one natural explanation for skin color differences has been presented as well as only one natural explanation for how a bacteria would develop resistance to a novel antibiotic.
That explanation is evolution (micro or adaptation or whatever you wish to call it) through natural selection of genetic variation.
So when, in science, one is asked to EXPLAIN how such things came about; one can either stand there like a slack-jawed moron - or they can explain natural phenomena utilizing natural forces and explanations - i.e. science.
Skepticism aside, supernatural causation of natural phenomena has NOT been a productive line of reasoning - all science, and thus all scientific advancement - has been through using NATURAL forces to explain natural phenomena.
IMO, whether one believes in ID or naturalism, experimentation involves theories, testability and repeatability. Of course, ID’ers have a reverence for life which would proscribe certain experiments from taking place. Cloning attempts, e.g. BTW, Your bitterness is shining through with your name-calling, Sir. Bob
If I take a single bacteria and let it grow, then plate it on ten plates and subject it to ten stresses; I can repeatably get it to “adapt”/”evolve” to be resistant to those ten different stresses through novel variations that are selected for in that environment.
Supernatural explanation for natural phenomena is a dead end that leads to no further information use or discovery.
Natural explanation for natural phenomena is called “science” and the technological world we live in owes it all to science - not supernaturalism.
The bacteria can transform their shapes, sure, but they remain bacteria. “Science”, BTW, has assured us in recent years that banning freon, DDT and incandescent bulbs, planting corn for fuel, “skyrocket”ing taxes to proscribe energy use, and marketing electric cars to cool the earth were all wonderful ideas. Not to mention the efficacy of solar panels and wind mills. To say I don’t trust government-sponsored PC “science” is an understatement. Bob
Supernatural explanations are a dead end.
Naturalistic explanations has lead to technology and increased useful and predictable knowledge about our world.
But nobody is going to force you to learn anything useful if you don't want to, you can rest assured of that!
I give you credit for persistence. My children are not random mixing of atoms, and until I see creatures created from scratch, I’m a tough sell. As the Bible says, we are fearfully and wondrously knit. Bob
DNA ensures that a living thing is not “a random assortment of atoms”, and if you knew about biology and DNA and what DNA does, you wouldn’t be hung up on such a ludicrous canard.
As the Bible says, I was created “from dust” and “to dust” I shall return. But I was also created using cellular processes involving DNA.
You apparently presume that when God said that Adam was created “from dust” that there was not ALSO an underlying physical process.
“If I take a single bacteria and let it grow, then plate it on ten plates and subject it to ten stresses; I can repeatably get it to “adapt”/”evolve” to be resistant to those ten different stresses through novel variations that are selected for in that environment.”
Why then, in the big Petri dish that is planet Earth, and in these billions of years, has the single-celled Plasmodium not evolved a resistance to cooler climates? Do you think you could grow Plasmodium under certain environmental stresses and “evolve” a variant of this parasite to be resistant to cooler climates?
What kind of environmental stress, or sequence of stresses, would result in uni-cellular organisms evolving into multi-cellular organisms. What survival advantage would result? Just what would the mutations conceivably be that would result in multti-cell organisms? Just saying mutations/selection/time doesn’t explain anything about how this would come to be.
As to what adaptations are needed, we can look at one celled life that forms cooperative colonies, or slime molds that exist unicellularly and then team up to form multi-cellular reproductive structures.
As with the eye, the “missing links” between are actually living among us.
MOVE THE GOAL POSTS:
I have been arguing that natural selection of genetic variation is the only scientific explanation for evolving resistance to novel antibiotics, skin color differences, and the INEVITABLE small changes in DNA that will accumulate between separate populations.
Unable, QUITE apparently, to deal scientifically with any of these subjects, the goal posts are moved so that the mechanism must also explain to your satisfaction every nonexistent creature that you think should exist, the rise of multi-cellular life, and perhaps also the origin of life itself?
That tactic sure seems to me like an admission on your part that the ONLY scientific explanation for skin color differences, development of antibiotic resistance, adaptation to the environment through changes in the DNA within the population - is natural selection of genetic variation.
Information is being CHANGED. Not lost or gained. CHANGED
Is information “lost” when the 2011 model of a car has less speed and performance but greater fuel economy?
And how does change of information prove evolution as understood in classical Darwinian terms?
I change everyday from younger to older. I am hence evolving in the Darwinian sense? CHANGE per se proves little for Darwin. No one, creationists included, denies that change exists. What sceptics want to see is INCREASED FUNCTIONALITY.
Regarding the car, well, I’m not sure how you could use that as an example because every single car I see has been DESIGNED INTELLIGENTLY by engineers to work the way they do.
As for the wordplay on evolution, I want an example of DARWINIAN EVOLUTION ( as we understand the term ) IN ACTION.
Citing methicillin resistance bacteria isn’t YET going to cut it. The functionality of the whole organism has NOT increased ( and that is what Darwinian Evolution entails). The immune system is a built in responce that was built-in that way. It clearly indicates a preexisting feedback mechanism built into the genome. The genome is ready to produce a vast array of antibodies to fight off a multitude of infections.
The novel adaptation in e. coli to digest citrate isn't a new function?
The ability to survive Methocillin through mutational change of an enzyme such that it could metabolize it, thus it can live, IS increased functionality.
Living in an environment where previous to the CHANGE you would die is a new function, that allows all other functions.
The reason I bring up cars is because of mechanical engineering and to illustrate that an new or increased function comes with a trade-off. BMW has some excellent engineers, but no amount of engine and body tweaking is going to make them able to create the fastest most high performance car on the road that ALSO gets the greatest fuel economy - and put it into production at a great price.
Evolution doesn't have a magical bag of tricks that can overcome the laws of physics. DNA codes for one of twenty amino acids that form a useful 3-D configuration that works with the electrochemistry.
Thus, as with a car, you can either have the fastest most efficient ribosome possible, or you have one that is fast and efficient enough - but can ALSO ‘drive through the mud’ in that it can survive the antibiotic that targets ribosomes.
So yes, new or increased functionality. No, no magic that overcomes the principle that there is no such thing as a free lunch.
Darwinian evolution, as the term is understood by those who understand the term - is this type of adaptive change allowing new function or survival in conditions that previously would be fatal - skin color change - metabolic adaptations to new conditions like the presence of nylon - etc etc.
THROUGH the mechanism of natural selection of genetic variation.
Any time there is a natural selective pressure that leads to a change in the DNA of a population that overcomes that pressure THAT is an example of Darwinian evolution.
Common descent of species is the accumulation of differences (quite slowly, reflecting a fidelity rate in copying DNA of 99.99997%) in separate populations of what was formerly the same species such that a 2% change in genetic DNA can make them two different species.
It is not like ‘and one day erosion happened and this valley formed’ or ‘and one day gravity happened and that star formed’; similarly it is not ‘and one day evolution happened and we had two different species’.
Yet the erosion we see is necessary and sufficient to explain geological formations.
The gravity we see is necessary and sufficient to explain the astrological formations and movements we see.
The INEVITABLE change and accumulation of change in separate species we observe is necessary and more than sufficient to explain a 2% difference in genetic DNA and a 6% difference in genomic DNA in two mammalian species over some six or seven million years.
“What survival advantages would result from being multi-cellular? That should be obvious.”
Well, they are not. A single cell organism that can reproduce asexually and very rapidly has the advantage. If survival was the key, we would all devolve to such organisms.
“I have been arguing that natural selection of genetic variation is the only scientific explanation for evolving resistance to novel antibiotics, skin color differences, and the INEVITABLE small changes in DNA that will accumulate between separate populations.”
I have no difficulty with this. Some driven by mutations and some driven by expression of information already present, I suspect. Call it evolution, I don’t care. But the mechanism that gives us bacterial resistance (broken genes), different skin color (expression of existine info perhaps), etc., is insufficient to explain the biological complexity we see.
The new goal posts, as you say, have to be dealt with because evolutionists claim that we have arrived at these goal posts via mutation/selection/descent. The evolutionist wants us to accept this without any demonstration. I don’t think they can even conduct a mind experiment to come up with the mutations required, in correct sequence, together with the environmental pressures that would result in each mutation predominating. The evolutionist tells us that all life evolved from a simple lifeform. Broken genes and adaptation using exsting info won’t get us there — not in 4billion years squared.
Over and out. Thanks for the discussion.
the mutations required, in correct sequence
Just because there are bacteria doesn't mean that elephants shouldn't exist. There is plenty of room in ‘bacteria world’ for huge multicellular organisms - we do not directly compete.
No, it is not insufficient to explain the biological complexity we see. This complexity is due to variation in DNA. Variation in DNA accumulates in separate populations.
You have done nothing to show how a 1% change in genetic DNA and a 6% change in genomic DNA over six million years would not be sufficiently explained by a fidelity rate of DNA copying of 99.99997%. Why, in fact, such a change would not be inevitable.
I don’t presume to know. What I do NOT believe is that our original “ancestors” progressed from a state of no consciousness to dim, then hazy, then clear consciousness over thousands, or millions of years. Same with the lower mammals.
BTW, do you believe that DNA formed by naturalistic processes as well, or did God will it into existence? Bob
I don’t presume to know, but if a naturalistic process whereby RNA/DNA could form a rudimentary life form were discovered it certainly wouldn’t shake my faith in God one wit.
That no more removes God as the creator of DNA than gravity and nuclear fusion means God did not create our Sun.
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