Saturday, 27 February 2016
Another failed Darwinian prediction IX
Biology is not lineage specific:
Evolution expects the species to fall into a common descent pattern. Therefore a particular lineage should not have highly differentiated, unique and complex designs, when compared to neighboring species. But this has been increasingly found to be the case, so much so that this pattern now has its own name—lineage-specific biology.
For example, transcription factors are proteins that bind to DNA and regulate which genes are expressed. Yet despite the importance of these proteins, their DNA binding sites vary dramatically across different species. As one report explained, “It was widely assumed that, like the sequences of the genes themselves, these transcription factor binding sites would be highly conserved throughout evolution. However, this turns out not to be the case in mammals.” (Rewiring of gene regulation across 300 million years of evolution) Evolutionists were surprised when transcription factor binding sites were found to be not conserved between mice and men, (Kunarso et. al.) between various other vertebrates, and even between different species of yeast. So now evolution is believed to have performed a massive, lineage-specific “rewiring” of cellular regulatory networks. (Pennacchio and Visel)
There are many more such examples of lineage-specific biology. Although flowers have four basic parts: sepals, petals, stamens and carpels, the daffodil’s trumpet is fundamentally different and must be an evolutionary “novelty.” (Oxford scientists say trumpets in daffodils are ‘new organ’) Out of the thousands of cockroach species, Saltoblattella montistabularis from South Africa is the only one that leaps. With its spring-loaded hind legs it accelerates at 23 g’s and out jumps even grass hoppers. (Picker, Colville and Burrows) An important immune system component, which is highly conserved across the vertebrates, is mysteriously absent in the Atlantic cod, Gadus morhua. (Star, et. al.) The brown algae, Ectocarpus siliculosus, has unique enzymes for biosynthesis and other tasks. (Cock) And the algae Bigelowiella natans has ten thousand unique genes and highly complex gene splicing machinery never before seen in a unicellular organism. It is, as one evolutionist explained, “unprecedented and truly remarkable for a unicellular organism.” (Tiny algae shed light on photosynthesis as a dynamic property)
Another fascinating example of lineage-specific biology are the many peculiar morphological and molecular novelties found in disparate, unrelated unicellular protists. As one study concluded, “Both euglenozoans and alveolates have a reputation for ‘doing things their own way,’ which is to say that they have developed seemingly unique ways to build important cellular structures or carry out molecular tasks critical for their survival. Why such hotspots for the evolution of novel solutions to problems should exist in the tree of life is not entirely clear.” (Lukes, Leander and Keeling, 2009a) Or as one evolutionist exclaimed, “this is totally crazy.” (Lukes, Leander and Keeling, 2009b)
References
Cock, J., et al. 2010. “The Ectocarpus genome and the independent evolution of multicellularity in brown algae.” Nature 465:617-621.
Kunarso G., et. al. 2010. “Transposable elements have rewired the core regulatory network of human embryonic stem cells.” Nature Genetics 42:631-634.
Lukes, J., B. Leander, P. Keeling. 2009. “Cascades of convergent evolution: the corresponding evolutionary histories of euglenozoans and dinoflagellates.” Proceedings of the National Academy of Sciences 106 Suppl 1:9963-9970.
Lukes, J., B. Leander, P. Keeling. 2009. “The corresponding evolutionary histories of euglenozoans and dinoflagellates: cascades of convergent evolution or accumulation of oddities?.” The National Academies. http://sackler.nasmediaonline.org/2009/darwin/julius_lukes/julius_lukes.html
“Oxford scientists say trumpets in daffodils are ‘new organ’.” 2011. BBC News February 28. http://www.bbc.co.uk/news/uk-england-oxfordshire-12598054
Pennacchio, L., A. Visel. 2010. “Limits of sequence and functional conservation.” Nature Genetics 42:557-558.
Picker, M., J. Colville, M. Burrows. 2012. “A cockroach that jumps.” Biology Letters 8:390-392.
“Rewiring of gene regulation across 300 million years of evolution.” 2010. ScienceDaily April 12. http://www.sciencedaily.com/releases/2010/04/100409093211.htm
Star, B., et. al. 2011. “The genome sequence of Atlantic cod reveals a unique immune system.” Nature 477:207–210.
“Tiny algae shed light on photosynthesis as a dynamic property.” 2012. ScienceDaily November 28. http://www.sciencedaily.com /releases/2012/11/121128132253.htm
Evolution expects the species to fall into a common descent pattern. Therefore a particular lineage should not have highly differentiated, unique and complex designs, when compared to neighboring species. But this has been increasingly found to be the case, so much so that this pattern now has its own name—lineage-specific biology.
For example, transcription factors are proteins that bind to DNA and regulate which genes are expressed. Yet despite the importance of these proteins, their DNA binding sites vary dramatically across different species. As one report explained, “It was widely assumed that, like the sequences of the genes themselves, these transcription factor binding sites would be highly conserved throughout evolution. However, this turns out not to be the case in mammals.” (Rewiring of gene regulation across 300 million years of evolution) Evolutionists were surprised when transcription factor binding sites were found to be not conserved between mice and men, (Kunarso et. al.) between various other vertebrates, and even between different species of yeast. So now evolution is believed to have performed a massive, lineage-specific “rewiring” of cellular regulatory networks. (Pennacchio and Visel)
There are many more such examples of lineage-specific biology. Although flowers have four basic parts: sepals, petals, stamens and carpels, the daffodil’s trumpet is fundamentally different and must be an evolutionary “novelty.” (Oxford scientists say trumpets in daffodils are ‘new organ’) Out of the thousands of cockroach species, Saltoblattella montistabularis from South Africa is the only one that leaps. With its spring-loaded hind legs it accelerates at 23 g’s and out jumps even grass hoppers. (Picker, Colville and Burrows) An important immune system component, which is highly conserved across the vertebrates, is mysteriously absent in the Atlantic cod, Gadus morhua. (Star, et. al.) The brown algae, Ectocarpus siliculosus, has unique enzymes for biosynthesis and other tasks. (Cock) And the algae Bigelowiella natans has ten thousand unique genes and highly complex gene splicing machinery never before seen in a unicellular organism. It is, as one evolutionist explained, “unprecedented and truly remarkable for a unicellular organism.” (Tiny algae shed light on photosynthesis as a dynamic property)
Another fascinating example of lineage-specific biology are the many peculiar morphological and molecular novelties found in disparate, unrelated unicellular protists. As one study concluded, “Both euglenozoans and alveolates have a reputation for ‘doing things their own way,’ which is to say that they have developed seemingly unique ways to build important cellular structures or carry out molecular tasks critical for their survival. Why such hotspots for the evolution of novel solutions to problems should exist in the tree of life is not entirely clear.” (Lukes, Leander and Keeling, 2009a) Or as one evolutionist exclaimed, “this is totally crazy.” (Lukes, Leander and Keeling, 2009b)
References
Cock, J., et al. 2010. “The Ectocarpus genome and the independent evolution of multicellularity in brown algae.” Nature 465:617-621.
Kunarso G., et. al. 2010. “Transposable elements have rewired the core regulatory network of human embryonic stem cells.” Nature Genetics 42:631-634.
Lukes, J., B. Leander, P. Keeling. 2009. “Cascades of convergent evolution: the corresponding evolutionary histories of euglenozoans and dinoflagellates.” Proceedings of the National Academy of Sciences 106 Suppl 1:9963-9970.
Lukes, J., B. Leander, P. Keeling. 2009. “The corresponding evolutionary histories of euglenozoans and dinoflagellates: cascades of convergent evolution or accumulation of oddities?.” The National Academies. http://sackler.nasmediaonline.org/2009/darwin/julius_lukes/julius_lukes.html
“Oxford scientists say trumpets in daffodils are ‘new organ’.” 2011. BBC News February 28. http://www.bbc.co.uk/news/uk-england-oxfordshire-12598054
Pennacchio, L., A. Visel. 2010. “Limits of sequence and functional conservation.” Nature Genetics 42:557-558.
Picker, M., J. Colville, M. Burrows. 2012. “A cockroach that jumps.” Biology Letters 8:390-392.
“Rewiring of gene regulation across 300 million years of evolution.” 2010. ScienceDaily April 12. http://www.sciencedaily.com/releases/2010/04/100409093211.htm
Star, B., et. al. 2011. “The genome sequence of Atlantic cod reveals a unique immune system.” Nature 477:207–210.
“Tiny algae shed light on photosynthesis as a dynamic property.” 2012. ScienceDaily November 28. http://www.sciencedaily.com /releases/2012/11/121128132253.htm
Another failed Darwinian prediction VIII
Serological tests reveal evolutionary relationships:
Early in the twentieth century scientists studied blood immunity and how immune reaction could be used to compare species. The blood studies tended to produce results that parallel the more obvious indicators such as body plan. For example, humans were found to be more closely related to apes than to fish or rabbits. These findings were said to be strong confirmations of evolution. In 1923 H. H. Lane cited this evidence as supporting “the fact of evolution.” (Lane, 47) Later in the century these findings continued to be cited in support of evolution. (Berra, 19; Dodson and Dodson, 65)
But even by mid century contradictions to evolutionary expectations were becoming obvious in serological tests. As J.B.S.Haldane explained in 1949, “Now every species of mammal and bird so far investigated has shown quite a surprising biochemical diversity by serological tests. The antigens concerned seem to be proteins to which polysaccharides are attached.” (quoted in Gagneux and Varki)
Indeed these polysaccharides, or glycans, did not fulfill evolutionary expectations. As one paper explained, glycans show “remarkably discontinuous distribution across evolutionary lineages,” for they “occur in a discontinuous and puzzling distribution across evolutionary lineages.” (Bishop and Gagneux) These glycans can be (i) specific to a particular lineage, (i) similar in very distant lineages, (iii) and conspicuously absent from very restricted taxa only.
Here is how another paper described glycan findings: “There is also no clear explanation for the extreme complexity and diversity of glycans that can be found on a given glycoconjugate or cell type. Based on the limited information available about the scope and distribution of this diversity among taxonomic groups, it is difficult to see clear trends or patterns consistent with different evolutionary lineages.” (Gagneux and Varki)
References
Berra, Tim. 1990. Evolution and the Myth of Creationism. Stanford: Stanford University Press.
Bishop J., P. Gagneux. 2007. “Evolution of carbohydrate antigens--microbial forces shaping host glycomes?.” Glycobiology 17:23R-34R.
Dodson, Edward, Peter Dodson. 1976. Evolution: Process and Product. New York: D. Van Nostrand Company.
Gagneux, P., A. Varki. 1999. “Evolutionary considerations in relating oligosaccharide diversity to biological function.” Glycobiology 9:747-755.
Lane, H. 1923. Evolution and Christian Faith. Princeton: Princeton University Press.
Early in the twentieth century scientists studied blood immunity and how immune reaction could be used to compare species. The blood studies tended to produce results that parallel the more obvious indicators such as body plan. For example, humans were found to be more closely related to apes than to fish or rabbits. These findings were said to be strong confirmations of evolution. In 1923 H. H. Lane cited this evidence as supporting “the fact of evolution.” (Lane, 47) Later in the century these findings continued to be cited in support of evolution. (Berra, 19; Dodson and Dodson, 65)
But even by mid century contradictions to evolutionary expectations were becoming obvious in serological tests. As J.B.S.Haldane explained in 1949, “Now every species of mammal and bird so far investigated has shown quite a surprising biochemical diversity by serological tests. The antigens concerned seem to be proteins to which polysaccharides are attached.” (quoted in Gagneux and Varki)
Indeed these polysaccharides, or glycans, did not fulfill evolutionary expectations. As one paper explained, glycans show “remarkably discontinuous distribution across evolutionary lineages,” for they “occur in a discontinuous and puzzling distribution across evolutionary lineages.” (Bishop and Gagneux) These glycans can be (i) specific to a particular lineage, (i) similar in very distant lineages, (iii) and conspicuously absent from very restricted taxa only.
Here is how another paper described glycan findings: “There is also no clear explanation for the extreme complexity and diversity of glycans that can be found on a given glycoconjugate or cell type. Based on the limited information available about the scope and distribution of this diversity among taxonomic groups, it is difficult to see clear trends or patterns consistent with different evolutionary lineages.” (Gagneux and Varki)
References
Berra, Tim. 1990. Evolution and the Myth of Creationism. Stanford: Stanford University Press.
Bishop J., P. Gagneux. 2007. “Evolution of carbohydrate antigens--microbial forces shaping host glycomes?.” Glycobiology 17:23R-34R.
Dodson, Edward, Peter Dodson. 1976. Evolution: Process and Product. New York: D. Van Nostrand Company.
Gagneux, P., A. Varki. 1999. “Evolutionary considerations in relating oligosaccharide diversity to biological function.” Glycobiology 9:747-755.
Lane, H. 1923. Evolution and Christian Faith. Princeton: Princeton University Press.
On the limits of intelligent design theory
Good Questions on the Nature of Intelligent Design
Ann Gauger February 25, 2016 6:01 AM
Earlier, Evolution News responded helpfully to a question from an email correspondent. Here are more questions and answers. A reader writes with a few good queries on the nature of ID theory.
Question:
On the complexity and specificity arguments, I've read that there are two arguments used as evidence for a designer's existence. However, do such arguments entail that the designer is still intervening in the ongoing development of the universe and of life within it? Or does ID only state that there was a designer at least at the very beginning, and ID as a theory does not categorically state (or necessarily entail) that this designer is still interested in making changes? Thus, are the complexity and specificity arguments examples rather than actual requirements?
Answer: ID is about design detection, and makes no statements about ongoing design or a design mechanism. We simply say that there are elements in the universe that give evidence of being designed. Anything further goes beyond what we can say. For example, we can say nothing about how (by what mechanism) design is instantiated. As for specified complexity and irreducible complexity, they are methods of design detection. I see irreducible complexity as a special case of specified complexity. There are probably other valid arguments for design, such as the fact that the universe is intelligible to us when there is no logical requirement that it be so.
Question:
Does ID associate any particular attributes with this "designer"? I am aware that various prominent ID proponents have said, on different occasions, yes and no -- and I do see a difference between a) ID theory itself, and b) personal opinion on aspects of the theory. The first is a necessary contingent on the theory itself. The second is not. My analogy for this is -- Christians believe certain things. Catholics accept the main Christian belief, plus a few other things.
Answer: ID posits nothing about the attributes of this designer, other than the fact that the designer must be capable of carrying out design at the appropriate scale. Anything more is personal opinion. As one leading ID scientist has written:
I myself do believe in a benevolent God, and I recognize that philosophy and theology may be able to extend the argument. But a scientific argument for design in biology does not reach that far. Thus while I argue for design, the question of the identity of the designer is left open. Possible candidates for the role of designer include: the God of Christianity; an angel -- fallen or not; Plato's demiurge; some mystical New Age force; space aliens from Alpha Centauri; time travelers; or some utterly unknown intelligent being. Of course, some of these possibilities may seem more plausible than others based on information from fields other than science. Nonetheless, as regards the identity of the designer, modern ID theory happily echoes Isaac Newton's phrase "Hypothesis non fingo"(I make no hypothesis).
(Michael Behe, "The Modern Intelligent Design Hypothesis," Philosophia Christi, Series 2, Vol. 3, No. 1 (2001), pg. 165)
Question:
Inherent in ID theory, is there the idea that there was purpose in the design? And, if so, what specific purposes?
Answer: ID also does not say anything about purpose, aside from the fact that things, especially biological things, look like they were made to carry out some particular function. They work together as a whole to make a functional organism. That functional organism is part of an ecosystem, and contributes to the functioning of that system. But is there an overall purpose to that system? To make a biosphere? This can be pushed out only so far; as to the reason for the existence of all of this -- why there should be such a planet, or the reason for our existence on the planet -- that goes beyond what ID can say. Final ends belong in the realms of philosophy and theology.
Question:
A personal question regarding how the ID debate has been fought. Why oh why was it based on biology??? IMHO, that was a terrible starting point! I would suggest later iterations and discussions focus on even more fundamental aspects of the universe. Time (apparently) is constant and measurable (not random and chaotic); the universal constant is just that -- a constant -- and without such a very, very limited range of variation, we could not exist (at least, not as we do now). Mathematics works -- again, in my thinking, a sign that this universe is rational; and if rational, designed (rationality and order from chaos...???). I know Plato et al. discussed this, but it seems to have been ignored in the ID debate. As I hope I have clearly indicated, I'm after answers that clearly differentiate ID as a theory in general from any personal takes on it (e.g., characteristics of the designer).
Answer: ID is not based purely on biology, though it may appear to be sometimes. The extreme fine-tuning of the universe for life; the fact that mathematics is rational and elegant, and fits the needs of science; the fact that chemistry is ordered so as to make its discovery possible, and that the planet is ordered so as to permit intelligent life to discover science at all (see The Privileged Planet) -- all these are arguments for design, design that is detectable by minds such as ours. I suggest reading A Meaningful World, by Benjamin Wiker and Jonathan Witt.
The reason it often appears that the argument is all about biology is because it is from there that the majority of pushback comes.
Thanks for your questions, and I hope my response helps.
Ann Gauger February 25, 2016 6:01 AM
Earlier, Evolution News responded helpfully to a question from an email correspondent. Here are more questions and answers. A reader writes with a few good queries on the nature of ID theory.
Question:
On the complexity and specificity arguments, I've read that there are two arguments used as evidence for a designer's existence. However, do such arguments entail that the designer is still intervening in the ongoing development of the universe and of life within it? Or does ID only state that there was a designer at least at the very beginning, and ID as a theory does not categorically state (or necessarily entail) that this designer is still interested in making changes? Thus, are the complexity and specificity arguments examples rather than actual requirements?
Answer: ID is about design detection, and makes no statements about ongoing design or a design mechanism. We simply say that there are elements in the universe that give evidence of being designed. Anything further goes beyond what we can say. For example, we can say nothing about how (by what mechanism) design is instantiated. As for specified complexity and irreducible complexity, they are methods of design detection. I see irreducible complexity as a special case of specified complexity. There are probably other valid arguments for design, such as the fact that the universe is intelligible to us when there is no logical requirement that it be so.
Question:
Does ID associate any particular attributes with this "designer"? I am aware that various prominent ID proponents have said, on different occasions, yes and no -- and I do see a difference between a) ID theory itself, and b) personal opinion on aspects of the theory. The first is a necessary contingent on the theory itself. The second is not. My analogy for this is -- Christians believe certain things. Catholics accept the main Christian belief, plus a few other things.
Answer: ID posits nothing about the attributes of this designer, other than the fact that the designer must be capable of carrying out design at the appropriate scale. Anything more is personal opinion. As one leading ID scientist has written:
I myself do believe in a benevolent God, and I recognize that philosophy and theology may be able to extend the argument. But a scientific argument for design in biology does not reach that far. Thus while I argue for design, the question of the identity of the designer is left open. Possible candidates for the role of designer include: the God of Christianity; an angel -- fallen or not; Plato's demiurge; some mystical New Age force; space aliens from Alpha Centauri; time travelers; or some utterly unknown intelligent being. Of course, some of these possibilities may seem more plausible than others based on information from fields other than science. Nonetheless, as regards the identity of the designer, modern ID theory happily echoes Isaac Newton's phrase "Hypothesis non fingo"(I make no hypothesis).
(Michael Behe, "The Modern Intelligent Design Hypothesis," Philosophia Christi, Series 2, Vol. 3, No. 1 (2001), pg. 165)
Question:
Inherent in ID theory, is there the idea that there was purpose in the design? And, if so, what specific purposes?
Answer: ID also does not say anything about purpose, aside from the fact that things, especially biological things, look like they were made to carry out some particular function. They work together as a whole to make a functional organism. That functional organism is part of an ecosystem, and contributes to the functioning of that system. But is there an overall purpose to that system? To make a biosphere? This can be pushed out only so far; as to the reason for the existence of all of this -- why there should be such a planet, or the reason for our existence on the planet -- that goes beyond what ID can say. Final ends belong in the realms of philosophy and theology.
Question:
A personal question regarding how the ID debate has been fought. Why oh why was it based on biology??? IMHO, that was a terrible starting point! I would suggest later iterations and discussions focus on even more fundamental aspects of the universe. Time (apparently) is constant and measurable (not random and chaotic); the universal constant is just that -- a constant -- and without such a very, very limited range of variation, we could not exist (at least, not as we do now). Mathematics works -- again, in my thinking, a sign that this universe is rational; and if rational, designed (rationality and order from chaos...???). I know Plato et al. discussed this, but it seems to have been ignored in the ID debate. As I hope I have clearly indicated, I'm after answers that clearly differentiate ID as a theory in general from any personal takes on it (e.g., characteristics of the designer).
Answer: ID is not based purely on biology, though it may appear to be sometimes. The extreme fine-tuning of the universe for life; the fact that mathematics is rational and elegant, and fits the needs of science; the fact that chemistry is ordered so as to make its discovery possible, and that the planet is ordered so as to permit intelligent life to discover science at all (see The Privileged Planet) -- all these are arguments for design, design that is detectable by minds such as ours. I suggest reading A Meaningful World, by Benjamin Wiker and Jonathan Witt.
The reason it often appears that the argument is all about biology is because it is from there that the majority of pushback comes.
Thanks for your questions, and I hope my response helps.
Darwinism vs, the real world XXXI
The Digestive System: The Stomach and Beyond
Howard Glicksman February 26, 2016 11:24 AM
Editor's note: Physicians have a special place among the thinkers who have elaborated the argument for intelligent design. Perhaps that's because, more than evolutionary biologists, they are familiar with the challenges of maintaining a functioning complex system, the human body. With that in mind, Evolution News is delighted to offer this series, "The Designed Body." For the complete series, see here. Dr. Glicksman practices palliative medicine for a hospice organization.
Except for molecular oxygen (O2), which comes in through the lungs, everything else the body needs to survive enters through the gastrointestinal system. This includes things like water, sugars, amino and fatty acids, cholesterol, electrolytes, minerals, and vitamins. But most of the nutrients the body needs are trapped inside more complex molecules, like carbohydrates, proteins, and fats, and are too large to enter the body. The gastrointestinal system must first break down these large molecules into much smaller ones, in a process called digestion, so it can then absorb the nutrients the body needs into the blood. In my last article I showed that digestion is similar to how a pulp and paper mill works. They both use mechanical and chemical means to break down large things into smaller ones and only use their equipment and chemicals when needed.
The process of digestion begins as soon as food enters the mouth. Its presence, along with its taste and smell, are detected by the nervous system, which stimulates the release of saliva from the glands in the mouth. Saliva contains the enzymes amylase and lipase, which begin the chemical breakdown of carbohydrates and fats respectively. As the food mixes with saliva, it is mashed by the teeth and the tongue, formed into a small mushy lump called a bolus, and moved back toward the pharynx.
Sensors in the pharynx detect the bolus and send information to the brain, initiating the swallow reflex. Swallowing involves the coordinated action of about twenty-five different pairs of muscles to protect the airway and propel the bolus into the esophagus, where it is moved by peristalsis down into the stomach. This article will show how the body follows the rules and takes control to continue digestion and absorption within the stomach and beyond.
Seeing, smelling, and tasting food causes the brain to send nerve messages to the stomach, which begins the first or cephalic phase of gastric secretion. This causes the release of mucous, hydrochloric acid, and pepsinogen. The mucous protects the cells that line the stomach from its own chemicals. The acid both kills microbes and converts pepsinogen into a powerful digestive enzyme called pepsin, a protease that begins to chemically breakdown protein. This phase also results in specialized cells in the stomach secreting a hormone called gastrin,which travels in the blood and tells the stomach cells to send out even more mucous, hydrochloric acid, and pepsinogen.
As the stomach fills up and distends with fluid, the stretch-sensitive mechanoreceptors in its walls send out more nerve messages. These stimulate the cells in the stomach to send out even more mucous, hydrochloric acid, and pepsinogen in what is called the second or gastric phase of gastric secretion. The contents of the stomach are then churned and mixed to further help in the digestive process, creating an acidic liquid called chyme.
It is important to note here that besides playing a major role in digestion, the stomach does two other important things: use its acid to help iron be absorbed later on and produce intrinsic factor to protect Vitamin B12 from being broken down by its acid. Both of these nutrients are needed for the production of hemoglobin.
The stomach absorbs very few nutrients (mainly water) and once it has done its part of digestion it passes the chyme into the first part of the intestine called the duodenum. To prevent damage to the duodenum and allow for more efficient digestion and absorption, it is important that the stomach control how fast it releases the chyme. This is accomplished by the pyloric sphincter, a ring-like band of muscle at the end of the stomach that is able to constrict and relax to send out the right amount of chyme for the right situation. Sensors in this region send messages to nerve cells, which help to control gastric emptying. In general, the more fat and protein is present and the more acidic the chyme, the slower the stomach empties its contents into the duodenum. This is why, when you have a heavier meal, your stomach feels full for a longer period of time.
As the stomach works on the acidic chyme and slowly sends it into the duodenum, the stretching of the intestinal walls signals it to start producing its own fluid. Intestinal juice mainly contains saline (NaCl), mucous, bicarbonate (HCO3-), and digestive enzymes. The alkaline bicarbonate begins to neutralize the acidic chyme that the intestine receives from the stomach. The enzymes produced in the lining of the intestine mainly help to break up the bonds between molecules that contain two sugars. Maltase breaks up the bonds between the two glucose molecules that make up maltose, lactase breaks up the bonds between glucose and galactose which make up lactose, and sucrase breaks up the bonds between glucose and fructose which make up sucrose. The intestine also produces enterokinase, a protease that is important for activating many of the enzymes that come from the pancreas.
As the chyme moves from the stomach into the duodenum, sensors on specialized gland cells detect simple molecules, like fatty and amino acids. The gland cells respond by sending out two hormones, secretin and cholecystokinin, to tell the pancreas to deposit its fluid into the digestive tract. Pancreatic juice contains high amounts of bicarbonate and is very alkaline. The addition of the alkaline pancreatic juice helps to further neutralize the acidic chyme that has entered the intestine from the stomach. The pancreatic juice also contains most of the enzymes needed to finish off the digestion of carbohydrates, fats, and proteins. In addition to amylases and various lipases, the pancreatic juice contains many different proteases that break down proteins. This includes trypsin, chymotrypsins, elastases, and carboxypeptidases. All of these proteases are produced inside the pancreatic cells in the inactive form so they won't digest the pancreas itself.
Trypsin enters the intestine as trypsinogen and becomes activated by its alkaline environment and enterokinase, which, by snipping a few atoms off, changes its shape so it is ready to go to work. Trypsin then activates the other enzymes and proteases, mentioned above. Finally, since lipids are not very soluble in water, they require the presence of bile from the liver and gall bladder to help in fat digestion. The presence of fatty acids in the duodenum contributes to the release of cholecystokinin, which tells the pancreas to release its juice and the gall bladder to contract and send its concentrated bile into the intestine to help in fat digestion.
The intestine, which consists of the duodenum, jejunum, and ileum, is where most of digestion and absorption take place. In addition to water, glucose, amino acids, cholesterol, and simple fats, the intestine also absorbs other vital chemicals, such as minerals, like calcium and iron, electrolytes, like sodium and potassium ions, and vitamins like A, C, D, E, K, and all of the B vitamins, including Vitamin B12. About 1.5 liters of fluid makes its way from the intestine into the colon daily, where mostly water, sodium, and chloride ions are reabsorbed. The remaining 100-150 gm of feces that daily exits the gastrointestinal tract through the rectum and anus usually consists of about 70 percent water and 30 percent solids from undigested plant fibers, like cellulose, cells shed from the lining of the gastrointestinal tract, and bacteria.
A quick review of gastrointestinal function shows that, to do its job properly, it needs separate control systems to turn on different organs, each using enough fluids and chemicals to adequately digest food and absorb enough nutrients. The cephalic and gastric phases of gastric secretion, along with gastrin, make sure the stomach sends out enough acid to activate pepsin for the digestion of proteins to begin. The amount of fatty and amino acids and the acidity of the chyme determine the rate of gastric emptying to help in proper digestion and absorption.
These chemicals also stimulate certain gland cells to release secretin and cholecystokinin, which together tell the pancreas to release its juices into the intestine and the gall bladder to release concentrated bile. Alkaline intestinal and pancreatic juices neutralize the acid coming from the stomach, which, with the help of enterokinase, activates trypsin. Trypsin then activates many other pancreatic enzymes that do most of the work of digestion. Bile from the liver and the gall bladder are needed to help fat digestion as well. Having completed digestion, the intestine then absorbs the nutrients that have been freed up. Finally, the intestine and colon reabsorb most of the water, sodium, and chloride ions that have been previously secreted so that very little is lost through the feces.
The total absence or significant deficiency of any one nutrient would have made it impossible for our earliest ancestors to survive long enough to reproduce. The gastrointestinal system demonstrates irreducible complexity because every component has to be present for it to be able to do its job. It also demonstrates natural survival capacity because each of its components has to provide enough of the right fluid and chemicals to cause adequate digestion and allow for the absorption of what the body needs for survival. Evolutionary biology usually points to similar systems within simpler organisms to explain how the gastrointestinal system may have come into being. Of course, this does not explain how the simpler systems developed in the first place or how it must work within the laws of nature to allow for survival.
The body must breathe in air every few seconds because its need for oxygen is so acute that without it, it dies in just a few minutes. When it comes to water, because the body is able to move some of it from its cells into the blood to compensate for its loss, it only has to drink fluids every few hours. What about glucose? After all, we know we don't have to take in glucose as often as oxygen or water to stay alive. So, how does the body go about making sure it has enough for its energy needs and how does evolutionary biology explain the development of the system it uses? That's what we'll start to look at next time.
Howard Glicksman February 26, 2016 11:24 AM
Editor's note: Physicians have a special place among the thinkers who have elaborated the argument for intelligent design. Perhaps that's because, more than evolutionary biologists, they are familiar with the challenges of maintaining a functioning complex system, the human body. With that in mind, Evolution News is delighted to offer this series, "The Designed Body." For the complete series, see here. Dr. Glicksman practices palliative medicine for a hospice organization.
Except for molecular oxygen (O2), which comes in through the lungs, everything else the body needs to survive enters through the gastrointestinal system. This includes things like water, sugars, amino and fatty acids, cholesterol, electrolytes, minerals, and vitamins. But most of the nutrients the body needs are trapped inside more complex molecules, like carbohydrates, proteins, and fats, and are too large to enter the body. The gastrointestinal system must first break down these large molecules into much smaller ones, in a process called digestion, so it can then absorb the nutrients the body needs into the blood. In my last article I showed that digestion is similar to how a pulp and paper mill works. They both use mechanical and chemical means to break down large things into smaller ones and only use their equipment and chemicals when needed.
The process of digestion begins as soon as food enters the mouth. Its presence, along with its taste and smell, are detected by the nervous system, which stimulates the release of saliva from the glands in the mouth. Saliva contains the enzymes amylase and lipase, which begin the chemical breakdown of carbohydrates and fats respectively. As the food mixes with saliva, it is mashed by the teeth and the tongue, formed into a small mushy lump called a bolus, and moved back toward the pharynx.
Sensors in the pharynx detect the bolus and send information to the brain, initiating the swallow reflex. Swallowing involves the coordinated action of about twenty-five different pairs of muscles to protect the airway and propel the bolus into the esophagus, where it is moved by peristalsis down into the stomach. This article will show how the body follows the rules and takes control to continue digestion and absorption within the stomach and beyond.
Seeing, smelling, and tasting food causes the brain to send nerve messages to the stomach, which begins the first or cephalic phase of gastric secretion. This causes the release of mucous, hydrochloric acid, and pepsinogen. The mucous protects the cells that line the stomach from its own chemicals. The acid both kills microbes and converts pepsinogen into a powerful digestive enzyme called pepsin, a protease that begins to chemically breakdown protein. This phase also results in specialized cells in the stomach secreting a hormone called gastrin,which travels in the blood and tells the stomach cells to send out even more mucous, hydrochloric acid, and pepsinogen.
As the stomach fills up and distends with fluid, the stretch-sensitive mechanoreceptors in its walls send out more nerve messages. These stimulate the cells in the stomach to send out even more mucous, hydrochloric acid, and pepsinogen in what is called the second or gastric phase of gastric secretion. The contents of the stomach are then churned and mixed to further help in the digestive process, creating an acidic liquid called chyme.
It is important to note here that besides playing a major role in digestion, the stomach does two other important things: use its acid to help iron be absorbed later on and produce intrinsic factor to protect Vitamin B12 from being broken down by its acid. Both of these nutrients are needed for the production of hemoglobin.
The stomach absorbs very few nutrients (mainly water) and once it has done its part of digestion it passes the chyme into the first part of the intestine called the duodenum. To prevent damage to the duodenum and allow for more efficient digestion and absorption, it is important that the stomach control how fast it releases the chyme. This is accomplished by the pyloric sphincter, a ring-like band of muscle at the end of the stomach that is able to constrict and relax to send out the right amount of chyme for the right situation. Sensors in this region send messages to nerve cells, which help to control gastric emptying. In general, the more fat and protein is present and the more acidic the chyme, the slower the stomach empties its contents into the duodenum. This is why, when you have a heavier meal, your stomach feels full for a longer period of time.
As the stomach works on the acidic chyme and slowly sends it into the duodenum, the stretching of the intestinal walls signals it to start producing its own fluid. Intestinal juice mainly contains saline (NaCl), mucous, bicarbonate (HCO3-), and digestive enzymes. The alkaline bicarbonate begins to neutralize the acidic chyme that the intestine receives from the stomach. The enzymes produced in the lining of the intestine mainly help to break up the bonds between molecules that contain two sugars. Maltase breaks up the bonds between the two glucose molecules that make up maltose, lactase breaks up the bonds between glucose and galactose which make up lactose, and sucrase breaks up the bonds between glucose and fructose which make up sucrose. The intestine also produces enterokinase, a protease that is important for activating many of the enzymes that come from the pancreas.
As the chyme moves from the stomach into the duodenum, sensors on specialized gland cells detect simple molecules, like fatty and amino acids. The gland cells respond by sending out two hormones, secretin and cholecystokinin, to tell the pancreas to deposit its fluid into the digestive tract. Pancreatic juice contains high amounts of bicarbonate and is very alkaline. The addition of the alkaline pancreatic juice helps to further neutralize the acidic chyme that has entered the intestine from the stomach. The pancreatic juice also contains most of the enzymes needed to finish off the digestion of carbohydrates, fats, and proteins. In addition to amylases and various lipases, the pancreatic juice contains many different proteases that break down proteins. This includes trypsin, chymotrypsins, elastases, and carboxypeptidases. All of these proteases are produced inside the pancreatic cells in the inactive form so they won't digest the pancreas itself.
Trypsin enters the intestine as trypsinogen and becomes activated by its alkaline environment and enterokinase, which, by snipping a few atoms off, changes its shape so it is ready to go to work. Trypsin then activates the other enzymes and proteases, mentioned above. Finally, since lipids are not very soluble in water, they require the presence of bile from the liver and gall bladder to help in fat digestion. The presence of fatty acids in the duodenum contributes to the release of cholecystokinin, which tells the pancreas to release its juice and the gall bladder to contract and send its concentrated bile into the intestine to help in fat digestion.
The intestine, which consists of the duodenum, jejunum, and ileum, is where most of digestion and absorption take place. In addition to water, glucose, amino acids, cholesterol, and simple fats, the intestine also absorbs other vital chemicals, such as minerals, like calcium and iron, electrolytes, like sodium and potassium ions, and vitamins like A, C, D, E, K, and all of the B vitamins, including Vitamin B12. About 1.5 liters of fluid makes its way from the intestine into the colon daily, where mostly water, sodium, and chloride ions are reabsorbed. The remaining 100-150 gm of feces that daily exits the gastrointestinal tract through the rectum and anus usually consists of about 70 percent water and 30 percent solids from undigested plant fibers, like cellulose, cells shed from the lining of the gastrointestinal tract, and bacteria.
A quick review of gastrointestinal function shows that, to do its job properly, it needs separate control systems to turn on different organs, each using enough fluids and chemicals to adequately digest food and absorb enough nutrients. The cephalic and gastric phases of gastric secretion, along with gastrin, make sure the stomach sends out enough acid to activate pepsin for the digestion of proteins to begin. The amount of fatty and amino acids and the acidity of the chyme determine the rate of gastric emptying to help in proper digestion and absorption.
These chemicals also stimulate certain gland cells to release secretin and cholecystokinin, which together tell the pancreas to release its juices into the intestine and the gall bladder to release concentrated bile. Alkaline intestinal and pancreatic juices neutralize the acid coming from the stomach, which, with the help of enterokinase, activates trypsin. Trypsin then activates many other pancreatic enzymes that do most of the work of digestion. Bile from the liver and the gall bladder are needed to help fat digestion as well. Having completed digestion, the intestine then absorbs the nutrients that have been freed up. Finally, the intestine and colon reabsorb most of the water, sodium, and chloride ions that have been previously secreted so that very little is lost through the feces.
The total absence or significant deficiency of any one nutrient would have made it impossible for our earliest ancestors to survive long enough to reproduce. The gastrointestinal system demonstrates irreducible complexity because every component has to be present for it to be able to do its job. It also demonstrates natural survival capacity because each of its components has to provide enough of the right fluid and chemicals to cause adequate digestion and allow for the absorption of what the body needs for survival. Evolutionary biology usually points to similar systems within simpler organisms to explain how the gastrointestinal system may have come into being. Of course, this does not explain how the simpler systems developed in the first place or how it must work within the laws of nature to allow for survival.
The body must breathe in air every few seconds because its need for oxygen is so acute that without it, it dies in just a few minutes. When it comes to water, because the body is able to move some of it from its cells into the blood to compensate for its loss, it only has to drink fluids every few hours. What about glucose? After all, we know we don't have to take in glucose as often as oxygen or water to stay alive. So, how does the body go about making sure it has enough for its energy needs and how does evolutionary biology explain the development of the system it uses? That's what we'll start to look at next time.
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