The Gastrointestinal System



Take a good look at yourself in the mirror.  Everything you see (and can't see) is made up of chemicals you had to first take into your body before they could be formed into the bones, organs, tissues, proteins and other vital molecules you need to survive. Chemicals like water, glucose and other sugars, salts, fats, amino acids, calcium and iron and vitamins, just to name a few. In fact, other than molecular oxygen (O2) that comes in through your lungs, all the other atoms and molecules your body needs to live, grow and work properly enter your body through the gastrointestinal system. In other words—you literally are what you eat.

It must be obvious to the clear-eyed unbiased observer that with such an important role to play in survival, the gastrointestinal system, with its ability to bring in such a diverse array of vital chemicals, and the body being able to use each of them properly to stay alive, can’t have been that “badly designed” otherwise where would be now?  But, as incredible as this may sound many Neo-Darwinian critics disagree.

They say that our body and its gastrointestinal system demonstrates “bad design” because other organisms can make essential molecules like vitamins, all of the amino acids and trace elements but we can’t so we have to make sure we have them in our diet otherwise we won’t function well enough to survive. And since the gastrointestinal system is not very efficient at bringing in certain minerals that this puts us at constant risk for debility and even death.

They tell us that all of this and more provides strong evidence for their theory—that life as we know it came about solely from the unguided and purposeless forces of natural selection acting on random genetic mutation—rather than there having been any intelligent design (ID) at work.

Of course, this “either/or” option is a false dichotomy, an intellectual straight-jacket with a large set of blinders into which only a committed Neo-Darwinist can fit. As if there were no alternative explanation(s) for the data. Maybe the “both/and” option applies here; that the origin of life as we know it involved some aspects of Neo-Darwinism and some (likely a lot more) aspects of ID.     

In this article I’ve chosen to cite just one critic, Dr. Nathan Lents, a professor of biology at John Jay College of Criminal Justice in New York City. The three composite quotes below come from his book “Human Errors: A Panorama of Our Glitches from Pointless Bones to Broken Genes”. 

In the second chapter, called “Our Needy Diet”, Dr. Lents does a marvelous job at explaining in great detail the difficulties we have in maintaining an adequate supply of many of the vital chemicals our body needs to survive. However, nowhere does he describe in detail, the different parts that make up the gastrointestinal system, what it actually takes for it to bring in these vital nutrients and how they’re controlled. One has to wonder how someone can critique the human body and the functional capacity of one of its organ systems without demonstrating to the reader their knowledge of what it takes to work properly.

To decry “Our Needy Diet” claiming that because it’s not up to snuff with other organisms as evidence of the human body and its gastrointestinal system’s “bad design” is ludicrous. What about the gazillions of other things that are needed for life? Oh, yes, for some of these that’s what Dr. Lents does in the rest of the book using the same technique; mostly complaints with limited if any praise reserved for (if he does deem it does work well enough) Evolution, blindly having made it so.

What the critic leaves out of his discussion turns out to be more important than what he says. His bias then leads him to a not surprising negative conclusion—as the name of his book implies—for it all seems to be just one big “sour grapes” argument against the human condition. It brings to mind the fact that there’s no other life form on the planet that can joyfully celebrate and with self-conceit boast of its intelligence while at the same time complain about having to use it to compensate for the “errors” it’s supposedly been dealt by chance. Unlucky us! Or should it be: Lucky us? What confusion! What irony!

What’s truly amazing however is how so many of the elements in the world are needed and used by our body to make the molecules it needs to survive—which as any engineer will tell you—if it works well enough to survive, it can’t have been that badly designed. By grossly misrepresenting what ID says about the design needed for life, Neo-Darwinists like Dr. Lents, have been pummelling this “straw man” for years. Let’s see what he has to say on this topic.

The Critic Speaks

Scurvy is a horrible disease caused by a deficiency in vitamin C. Without vitamin C, the ECM (extracellular matrix = connective tissue) gets weak and our bodies basically fall apart. Humans and other primates are nearly alone in the need for dietary vitamin C because, somewhere in our evolutionary past (we) lost the ability to make this micronutrient. The broken gene GULO that codes for an enzyme (gulonolactone oxidase) responsible for a key step in the manufacture of vitamin C is broken. This begs the question: Why wasn’t the GULO gene mutation eliminated? Scurvy is fatal. The consequences of this mutation ought to have been quick and harsh and should have prevented the harmful error from spreading throughout the species. (But), what if this disrupting mutation happened in a primate, who, purely by chance, already had lots of vitamin C in her diet? For her, there would be no consequence of losing the ability to make vitamin C since she already ate foods that contained it. After all, while it’s easy to break a gene by mutation, it’s much more difficult to fix it. But even though we have learned to eat food with ample vitamin C we have not managed to fully compensate for this malfunction. It’s still a very poor design.     

Other essential vitamins can give us just as much trouble as vitamin C. Take vitamin D. The commonly ingested form of vitamin D is not fully active, which means that we can’t use it until it’s processed in the liver and kidney. The precursor of the vitamin is also generated in the skin, providing the individual gets enough sunlight, but it still needs to be processed into the active form. Without enough dietary vitamin D or enough sunlight, young humans can develop a disease called rickets, and older humans can develop osteoporosis. Both of these conditions involve brittle and deformed bones, which can be extremely painful. Humans need calcium to keep bones strong, and we need vitamin D to help absorb calcium from food. We could eat all the calcium in the world and none of it would be absorbed without sufficient vitamin D. It could be argued that this is not a problem of poor design, per se, but it’s certainly not good design. The complex multistep activation path for vitamin D is obnoxious. The domestication of animals for meat and eggs mostly solved the problem of rickets. This is just one example of human ingenuity overcoming the design limitations of the human body.

The most commonly known role of iron is in the functioning of hemoglobin, the protein that transports oxygen throughout our bodies. That iron deficiency is pandemic in a world filled with iron is paradoxical, to say the least. Once again, poor design is mostly the blame for the body’s (iron) problems. To start with, the human gastrointestinal tract is terrible at extracting iron from plants as compared to other animals (whose) intestines do just fine. The frustrating part is that we don’t completely understand why it’s so hard for us to get enough iron. Deficiencies of other heavy metals are rarer than iron deficiency, mostly because we need so little of those minerals like copper, zinc, cobalt and nickel. Nevertheless, trace amounts of these heavy metals are crucial, and a diet completely devoid of them would eventually be lethal. Was it an evolutionary error that made it so hard for humans to absorb them, or was it just a failure to adapt to this challenge? Is there a difference? There are plenty of microorganisms that simply have no need for many of these elements. For every one of these elements there are organisms that have engineered their own molecules to perform those elements’ jobs. Humans haven’t done much of that and so we require a broad variety of trace metal ions.   

Filling in the Gaps

Digestion and Absorption: How it Works

As noted above, except for molecular oxygen (O2), which comes in through the lungs, everything else your body needs to survive enters through the gastrointestinal system. The seven types of molecules your body uses to get what it needs into the blood through the gastrointestinal system are water, carbohydrates, fats, proteins, salts, minerals, and vitamins. 

Water provides your cells with the right size, acts as a solvent for its vital chemicals at their specific concentrations and facilitates proper function while for your body it provides enough blood volume resulting in enough blood flow to feed the tissues well enough by surrounding the cells, acting as a conduit for the chemical exchange between them and the circulation at the level of the capillary.

Carbohydrates are made up of sugar molecules (e.g. glucose) which your body uses as its main source of energy and joins to other molecules to make things like DNA and RNA and important parts of your connective tissue and nerve insulation.

Fats consist of fatty acids joined to glycerol which your body uses as an alternative source of energy, cushioning for pressure areas and to make the cell membrane and the insulation that surrounds your nerves to help them work properly. 

Proteins are made up of 20 different amino acids which your body uses to make all the cellular structures and molecular machinery, including enzymes which speed up chemical reactions, the actin and myosin that allow for muscle contraction, antibodies to fight infection, clotting and anti-clotting factors, and the hormones needed to control body development and the metabolism. 

Salts (e.g. sodium and potassium chloride) are the main atoms that dissolve in your body’s water as ions which maintain not only all cell function and blood volume but also specifically nerve, muscle and gland function as well. 

Minerals (e.g. calcium, phosphorus, iron, copper and zinc) are used to make connective tissue like bone, the O2 transport protein hemoglobin along with playing an important structural and functional part of certain enzymes and other proteins needed for critical chemical reactions.   

Vitamins (e.g. B vitamins, A, C, D, E and K) are molecules your body can’t produce but needs for some of its vital chemical reactions and structures.     

When it comes to getting these chemicals into your blood the gastrointestinal system faces a dilemma. Many of the nutrients your body needs are chemically trapped inside larger more complex molecules that because of their size and other factors cannot be brought into the body. The gastrointestinal system must first breakdown these large molecules into much smaller ones, in a process called digestion, so it can then bring the chemicals the body needs into the blood through a process called absorption. To do this it requires many different parts. These include the mouth, teeth, tongue, salivary glands, pharynx, esophagus, stomach, intestine, pancreas, liver, gall bladder, colorectum, and anus (see above). Here's something Dr. Lents never mentions in his book—how it all works.

Just as your body has a respiratory center that tells you to breathe in air, and a thirst center that tells you to drink water, it also has a hunger center that tells you to eat food.  Understanding it is still a work in progress, but scientists think that there are centers within the brain that receive information (through nerves and hormones) about blood glucose and fat stores, stretching of the stomach wall, and nutrients being released into the intestine.  The brain takes this information and, with emotional and other factors, decides when to signal the hunger center to tell you to eat.

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 contents of the mouth mixes with saliva, it is worked on 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 brainstem which initiates the swallow reflex. Swallowing involves the coordinated action of over forty 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. (For a more thorough description see "The Pharynx (Throat)" )

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 (HCl) and pepsinogen. The mucous protects the cells that line the stomach from its own chemicals and the acid not only kills microbes but also converts pepsinogen into a powerful digestive enzyme called pepsin, a protease that begins to chemically breakdown protein into its individual amino acids. This phase also results in specialized cells in the stomach secreting a hormone called gastrin. It travels in the blood and attaches to specific receptors in the cells of the stomach and tells them to send out even more mucous, HCl 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, HCl 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 to help in the digestive process resulting in an acidic liquid called chyme

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 chemical 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. The more fat and protein present and the more acidic the chyme, the slower the stomach empties its contents. This is why when you have a heavier meal your stomach feels fuller 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, sodium bicarbonate (NaHCO3) 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 breaks down proteins and is important for activating many of the enzymes that come from the pancreas.

As the chyme moves from the stomach into the duodenum, simple molecules, like fatty and amino acids, are detected by sensors on specialized gland cells which respond by sending out two hormones, secretin and cholecystokinin. They travel in the blood and attach to receptors in the pancreas telling it to deposit its fluid into the digestive tract. Pancreatic juice contains high amounts of NaHCO3 and is very alkaline. The addition of the alkaline pancreatic juice helps to further neutralize the acidic chyme that has come into the intestine from the stomach. It 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 proteases that break down proteins. This includes trypsin, chymotrypsins, elastases and carboxypeptidases. All of these enzymes are produced in the inactive form so they won’t digest the pancreas itself but once released from there become activated in the intestine. 

Trypsin enters the intestine as trypsinogen and becomes activated by its alkaline environment and by enterokinase which by snipping a few atoms off changes its shape making it ready to go to work. It then activates the other proteases mentioned above and other enzymes as well.  Finally, since lipids are not very soluble in water they require the presence of bile, which comes from the liver and gall bladder, to help in fat digestion. As noted above, the presence of fatty acids in the duodenum contributes to the release of cholecystokinin which tells the pancreas to release its juice. But it also attaches to receptors in the gall bladder telling it 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 which include 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 and 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% water and 30% solids from undigested plant fibers, like cellulose, cells shed from the lining of the gastrointestinal tract, and bacteria.

It’s important to note here that the significant malfunction or absence of almost any one of the abovementioned components of gastrointestinal function would render the body at high risk of debility and death. In other words, almost everything noted above must be in place and in proper working order for human survival.

We’ve just looked at one aspect of gastrointestinal function (how digestion and absorption take place). Logic dictates that this should have been described in detail by Dr. Lents, rather than being totally neglected, before making a conclusion of its “bad design”. The next thing we’ll look at is how the intestinal cell (enterocyte) absorbs the seven different types of chemicals your body needs. It doesn’t just take place by magic—it does take foresight and planning—and lots of different parts.   

Intestinal Absorption: How it Works

The intestine is about 20 feet long and has three parts: the duodenum, jejunum and ileum. It has numerous folds and wrinkles each with multiple projecting finger-like villi. The villi are each lined with epithelial cells (enterocytes) which each have multiple microvilli that project into the surrounding luminal fluid. This set-up maximizes the surface area (said to be the size of a tennis court) for the absorption of the seven different types of chemicals by the enterocytes most of which takes place in the jejunum. And the enterocytes are specially equipped to do their jobs.
Water is able to freely diffuse from the lumen through the cell membrane of the enterocyte and then be sent out at the other end into the blood.  

Sugars, after having been broken down to simple molecules, require membrane-bound transporters or diffusion facilitators to pass from the lumen into the enterocyte and from there into the blood.

Fats, after having been broken down to simpler molecules and emulsified by bile, form micelles which move from the lumen into the enterocyte where they are transformed into more complex lipid molecules and sent out to the blood.

Proteins, after having been broken down into individual amino acids or combinations of no more than two (dipeptide) or three (tripeptide) require membrane-bound active transporters to enter the enterocyte where they all become individual amino acids that can diffuse into the blood.  

Salts, like sodium and potassium in solution, become +ve ions which require membrane bound active transporters to enter the enterocyte and pass from there into the blood.

Minerals, like calcium, iron, zinc and copper, need specific membrane bound transport proteins to get into the enterocyte and then to exit it into the blood.

Vitamins, the lipid soluble ones, A, E, D, K, are taken up into the enterocyte along with dietary fats in micelles and then pass into the blood. The water soluble ones, like B vitamins and vitamin C, require membrane bound specific carriers to be transported into the enterocyte and to then exit into the blood. One exception is vitamin B12. It’s a large molecule. To prevent it from being digested, it bonds to intrinsic factor (IF) in the stomach and then this B12-IF complex attaches to a specific receptor in the ileum where it enters the enterocyte and from there goes into the blood.   

So you can see that the ability for the gastrointestinal system to bring in all the chemicals you need to live requires not only digestion to break them down from complex molecules but also specific membrane bound transport systems to get them into the enterocyte and from there into the blood.

But there’s one more issue that Dr. Lents never brings up in his chapter on “Our Needy Diet”. He is correct in saying that we are always at risk of dietary insufficiency, but in general he neglects to mention that for some nutrients having too much is not a good thing either, as it can lead to toxicity, debility and death.

We’ll now take a look at that as it applies to calcium and iron. As you can imagine, it’s going to require some sort of control mechanism in place to achieve the fine tuning needed to manage these elements.

Calcium Control

Having enough calcium in the body is important for having strong bones. But the amount of calcium in your blood and in your cells also plays an important role in nerve, muscle and gland function. In fact, a 50% up or down change in the serum calcium level results in death.

The main control of calcium in your body is done by the parathyroid glands embedded in the four corners of the thyroid gland in your neck. Using calcium-sensing receptors (Ca-SR) in their cell membrane the parathyroid gland cells monitor the serum calcium. Their response is an inverse one: a drop in calcium causes an increase in the output of parathormone (PTH) and a rise in calcium causes a decrease in PTH.

To maintain calcium control PTH works to increase the amount of calcium in the blood by attaching to specific receptors that ultimately affects your bones, kidneys and gastrointestinal system. More PTH tells the bones to release more calcium into the blood and the kidneys to bring back more calcium from the urine presently in production. Less PTH does the opposite. When it comes to the gastrointestinal system PTH affects how much calcium the intestine is able to absorb by controlling how much calcitriol (activated vitamin D3) is formed.

The vitamin D3 (D3) you produce in your skin after being exposed to sunlight or bring into your gastrointestinal system by your diet goes through the process of activation by first being acted on by the liver and then the kidney. D3, does not dissolve well in blood and must first attach to a specific carrier protein made in the liver to be transported throughout the body. The liver begins the activation of D3 by adding a hydroxyl (OH) group to its 25th carbon. This 25(OH)-D3 then gets transported to the kidneys where another OH group is added. Depending on the calcium needs of the body, the OH is added to either the 24th carbon, to form 24,25 (OH)2-D3 which is relatively inactive or to the 1st carbon, to form 1,25 (OH)2-D3 which is the activated form called calcitriol.  Calcitriol then attaches to specific receptors in the nucleus of the enterocytes and signals them to absorb more calcium. In a normal diet this can increase the calcium absorption from 10% to 30% and in ones with very low calcium up to 90%!

To recap: based on the ongoing calcium needs of the body it is PTH that tells the kidneys which carbon on the 25(OH)-D3 that comes to it from the liver (the 1st or 24th) should be placed the 2nd OH. If it is added to the 24th, it becomes 24, 25(OH)2-D3 which is relatively inactive whereas if it is added to the 1st it becomes 1,25 (OH)2-D3 which is the activated form called calcitriol. That’s how PTH affects the gastrointestinal absorption of calcium to help maintain calcium control. By the way, the absence of Ca-SRs, PTH or PTH receptors is incompatible with life. Just thought you’d want to know—bad design or not.   

Iron Control

Iron is very important for human life as among other functions it is the metal in hemoglobin that allows it to transport O2 throughout the body. However, due to its chemical nature iron tends to be toxic and so needs to be transported and closely controlled in the body. It’s only in the last few decades that medical science has figured out how some of this works. As it turns out, the liver plays a major role in iron metabolism as it produces a carrier protein that allows iron to be transported in the blood and also sends out a hormone that controls how much iron the body brings into the blood through the gastrointestinal system.  

Iron enters the duodenal enterocytes through a specialized membrane bound transport molecule. But once inside the enterocyte it doesn’t automatically get sent out into the blood. To do that it has to pass through an outgoing transporter called ferroportin. Once iron enters the blood it gets picked up by transferrin, a transport protein made in the liver. Transferrin safely carries the iron throughout the body, mostly to the developing red blood cells in the bone marrow, where it attaches to specific receptors and drops off its payload.

The ferroportin outgoing transporter in the enterocyte is controlled by a hormone made in the liver called hepcidin. There seems to be many different factors that affect how much hepcidin the liver cells release. Some of these factors include anemia, low serum iron levels, hypoxia (low oxygen) and inflammation.

Hepcidin travels in the blood and attaches to the ferroportin transporter instructing it to not let the iron pass out of the enterocyte into the blood. In other words, hepcidin acts as a negative factor for iron absorption. The iron stays inside the enterocyte and is eventually released from the body when these cells are shed from the duodenum. It now appears that defects in hepcidin and/or the ferroportin transporter in the enterocyte may contribute to various diseases that affect iron in the body. 

To recap: the liver plays a major role in taking control of iron in the body. Not only does it produce a transport protein (transferrin) that safely carries iron to the bone marrow so it can be used by developing red blood cells to make hemoglobin, it also sends out hepcidin which controls how much iron the enterocytes send into the blood. It’s only in the last few decades that medical scientists have come to realize that conditions involving hepcidin and/or the ferroportin transporter in the enterocyte may be responsible for the various types of iron related anemias and overload situations—in other words, it’s not as simple as it looks.

Three Questions

So, as humans we do have a needy diet. So what? It’s evident that to get what we need from outside our body to inside where it can be used to keep us alive requires a lot of complicated organs using numerous different chemicals and membrane bound transport proteins. This is important stuff that’s barely even mentioned by our critic and if so, with limited detail and then to only complain about it. To then point out some perceived insufficiencies and then claim from that that our body and the gastrointestinal system came about by the unguided and purposeless forces of natural selection acting on random variation (genetic mutation) seems a tad inappropriate. To jump to this conclusion without pointing out what else is involved  and needs to be explained is frankly not only disingenuous but unscientific. In fact, it’s a non sequitur which in and of itself does nothing to prove the Neo-Darwinian point of view. Here are three questions to which this critic doesn’t even allude, never mind try to answer, which should give the reader pause.
In what order and from where did the new genetic and other information come that specifies the size, shape, assembly, specifications and control of all of the parts of the gastrointestinal system to allow it perform the important function of digestion and given that each part is absolutely needed for survival what is the real probability that it could have come about by undirected forces while remaining functional in intermediate organisms each step along the way? 

In what order and from where did the new genetic and other information come that specifies the different parts of the enterocyte that allows it to absorb all the different types of chemicals our body needs to function and survive and given that each chemical is absolutely needed for human survival what is the real probability that this could have come about by undirected forces while remaining functional in intermediate organisms each step along the way? 

In what order and from where did the new genetic and other information come that specifies the different parts of the control mechanisms in the body for chemicals like calcium and iron (and others as well), which must be fine-tuned to stay within narrow ranges for survival and given that each is necessary for human survival what’s the real probability that they could have come about by undirected forces while remaining functional in intermediate organisms each step along the way?

So, are you willing to accept the undirected forces of natural selection acting on random variation as the definitive answer to the above questions?  The “smoke and mirrors” of Neo-Darwinism which doesn’t even try to account for the simultaneous development of all of the digestive and absorptive components needed for the gastrointestinal system to work properly never mind some of the abovementioned control systems.

It’s important to realize that natural selection acting on random variation (genetic mutation) means exactly what it says. Over time, life required a gazillion bits of new genetic information (not natural selection) to bring about new structures with new functions. All natural selection did was preserve the life that was up and running properly and able to survive due to these gazillion undirected genetic mutations. But keep in mind, natural selection cuts both ways.

Based on what we know about how life actually works Neo-Darwinism may explain the survival of the fittest but not the arrival of the fittest. That’s because when it comes to survival, logic tells us that the same power that natural selection had to preserve human life when the gastrointestinal system could digest and absorb all the chemicals the body needs to survive along with maintain control of important chemicals would have also prevented it from surviving if any one of the parts of these systems were missing, misplaced or defective.

The known engineering principles needed to bring about the functional capacities of all of these parts that resulted in human existence means that, in principle, not only does Darwin’s theory of gradualism fail, but so do all the other Neo-Darwinian attempts to replace it. What do you think?


Starting with a derivative of glucose there are several different chemicals and specific enzymes needed for mammals to make vitamin C (see below). The next to last chemical in the series before becoming vitamin C is “L-Gulonolactone” which needs to be acted upon by the #6 enzyme in the figure below “L-Gulonolactone oxidase” (GULO). This is the enzyme in humans and most primates that is defective so they can’t make vitamin C. 

As Dr. Lents tells us the broken gene GULO that codes for an enzyme (gulonolactone oxidase) responsible for a key step in the manufacture of vitamin C is broken. This begs the question: Why wasn’t the GULO gene mutation eliminated? Scurvy is fatal. The consequences of this mutation ought to have been quick and harsh and should have prevented the harmful error from spreading throughout the species. (But), what if this disrupting mutation happened in a primate, who, purely by chance, already had lots of vitamin C in her diet? For her, there would be no consequence of losing the ability to make vitamin C since she already ate foods that contained it. After all, while it’s easy to break a gene by mutation, it’s much more difficult to fix it.

On the face of it, it certainly does look like at some point in time the GULO gene became defective so that humans and other primates couldn’t make their own vitamin C. But one has to wonder even if the first primate to experience this may have been lucky enough to have lots of vitamin C in her diet and could absorb it through her intestine by having the membrane bound transport protein needed for the task it does not explain why this defective GULO gene came to dominate the species. Dr. Lents said she must have been lucky enough to already have lots of vitamin C in her diet when her GULO gene bit the dust. But what did that have to do with all of the other primates around her who could still make their own vitamin C? Why did natural selection make them all eventually lose that ability too? In other words, what advantage did the defective GULO gene give her and her descendents? Dr. Lents does not even mention this but others have considered it.

One group of scientists wondered if this gave our species an advantage because the final reaction to form vitamin C spins off hydrogen peroxide (H2O2) a reactive oxygen species which can be detrimental so we brought into the body from the intestine instead. Another group wondered if rather than being a defective gene GULO has a yet unknown epigenetic role to play in gene expression. After all, one has to wonder if L-Gulonolactone and/or GULO in fact have some sort of function in the body or not?  Nobody seems to know (or care).

As noted above, it certainly looks like our loss of producing vitamin C could have occurred because of genetic mutation of the last of the enzymes needed in the reactions to turn glucose to vitamin C.  But how did these reactions in other mammals come together to form vitamin C in the first place? According to Dr. Lents it was easy for the undirected purposeless forces of natural selection acting on genetic mutation to come up with the biosynthesis of vitamin C. But on the face of it, it does look like it was pretty complicated as it involved numerous specific chemicals being successively acted upon by specific enzymes. So, if it was as simple as Dr. Lents leads us to believe then why is it so hard to fix it if just one of them fails? Nothing simple seems to be going on there.

Finally, one has to keep in mind that vitamin C production, whether in the kidneys of reptiles and birds, or the liver in mammals, and/or the ability for the intestine to absorb it by way of a specific membrane bound transporter, would have had to have been in place before animals could produce the collagen needed to support these tissues. In other words, if there’s no vitamin C production in the kidneys or liver and/or absorption from the gastrointestinal system, then there’s no collagen around to support the kidneys, the liver and the gastrointestinal system. As Dr. Lents said earlier without vitamin C our bodies basically fall apart.

It certainly looks like there’s a lot of causal circularity going on here. If without A you can’t have B. But you need B to have A. Then what? Well, then you make up an Evolutionary tall tale and hope nobody notices.  Good job!

When it comes to the calcium metabolism and how the body controls it we are told by Dr. Lents that vitamin D plays a major role but that the complex multistep activation path for vitamin D is obnoxious. What exactly does he mean by this? Is he saying that the process should be easier? As noted above, the process seems pretty nifty. The parathyroid glands monitor and control serum calcium and when they think the body needs more of it they make sure the kidneys fully activate vitamin D by producing 1,25 (OH)2-D3 so the intestine can absorb more calcium. And when they think the body needs less calcium they produce 24,25 (OH)2-D3 a much less active form instead. Rather than recognizing the beautiful control mechanism that had to have been in place to maintain our serum calcium and with it proper nerve, muscle and gland control—in other words our survival—Dr. Lents instead congratulates us for the domestication of animals for meat and eggs (having) mostly solved the problem of rickets as just one example of human ingenuity overcoming the design limitations of the human body. Yes, that was very important. But without all the parts needed to control the serum calcium being located where they needed to be, doing what they’re supposed to do, fixing rickets would not only have been a moot point, it would have been doggone impossible. Design limitations my foot!   

Dr. Lents is right in stating that iron deficiency is pandemic in a world filled with iron is paradoxical, to say the least. He then asserts that poor design is mostly the blame for the body’s (iron) problems. Nowhere does he mention that iron, like all the heavy metals, must be managed very carefully by the body because they walk a fine line between deficiency and toxicity, never mind each of them being absolutely necessary for human life. Yet, he tells us that there are plenty of microorganisms that simply have no need for many of these elements. For every one of these elements there are organisms that have engineered their own molecules to perform those elements’ jobs. Humans haven’t done much of that and so we require a broad variety of trace metal ions.  

It is humorous to see that Dr. Lents has already come to the conclusion about iron deficiency in the world being due to poor design when the experts admit that this a very complicated situation and in fact are just in the midst of figuring out how the body controls iron anyway. And aren’t we lucky that our body figured out that, as opposed to many microorganisms, it needs all of these trace metals and has ways of getting them without causing toxicity?

It must be wonderful to be as assured as Dr. Lents and his cronies who, even though there is still so much to learn about how life works, claim to know how it came into existence while, despite this universal ignorance feel qualified to criticize human life as having been badly designed. “Me thinks they dost protest too much”—a famous expression from a million monkeys typing on a million typewriters for a million years—no doubt!

Laufmann’s Triple Filter

Not understanding the objectives of the designer

At bottom, the most important thing to the designer is for life to be able to survive long enough to reproduce. This means that to do this, no matter the organism, it has to have the cellular and organic structures in place and be able to get and use the chemicals it needs. Experience tells us that life is not autonomous. It is dependent on something other than itself, whether it be sunlight, water, other chemicals, and even other life. The struggle for survival is part and parcel of life and the very fact that so many species exist indicates that to a large degree the designer’s objectives have largely been met. And in particular, humanity has been given a special intelligence that allows it to not only recognize these facts, allowing it to solve the problems of survival, but also the ability to reflect on them in a positive or negative light—whether it be an attitude of gratitude or one of criticism. Unfortunately, our critic, although making some important and valid points about the true nature of the human condition tends to oversimplify how it could have come about while constantly complaining about it. 

Not accounting for the functional requirements, constraints and trade-offs

Many different organisms have many different ways of getting what they need to survive. Given the functional requirements of the human body and the physical and chemical constraints it is under to get what it needs to survive and reproduce the size, shape, and location of the various parts that make up the gastrointestinal system represent the trade-offs that had to be made for it to fit into its space and still function well enough to get the job done. In particular, when it comes to getting enough vitamin C&D and controlling our calcium and iron, never mind everything else it needs to survive, our gastrointestinal system is a wonder!

Failure to acknowledge user abuse and degradation over time

Having a gastrointestinal system that, if properly managed, is capable of providing the body with the chemicals it needs to survive and reproduce does not preclude it from being abused or degenerating. Purposely not eating the right kinds of food to make sure the body has what it needs cannot be attributed to the gastrointestinal system itself. Likewise, taking in chemicals that have the potential to cause damage or suffering from diseases like infection or infestation are outside the purview of the digestion and absorption functions. Over time, like all living tissues, efficiencies may wane and so negatively impact function and survivability. Join the club!  


The human condition does involve intelligence and hard work. It also requires having several different organs in place, like the ones that make up the gastrointestinal system, to be able to get, through “our needy diet”, what it requires to survive and reproduce. To claim, as Dr. Lents and many of his colleagues do, that this represents “bad design” because they perceive that there are other organisms better off than we are, at least in this regard, is not only misguided but, based on engineering principles, totally absurd. What do you think?  

Also see Dr. Glicksman's Series on

"Beyond Irreducible Complexity"

"Exercise Your Wonder"

"On Being Alive"

Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.

Comments and questions are welcome.

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