In a dramatic triumph of medical science, some children with this condition—known as transposition of the great vessels—can now be saved. Surgeons must slice out several of the vessels and swap them around in order to match their strength, thickness, and elasticity to the load they must bear when the blood is flowing correctly. This has to be done while the infant is on total heart-lung bypass, so it is incredibly risky to perform on a baby that is just hours or days old. Nowadays, most children do survive the procedure and live relatively normal lives. What nature has goofed up, science can now correct.
While holes in the heart and transposed vessels are life-threatening but rare defects in the formation of the cardiovascular system, there are subtler malformations that are much more common—and that can be every bit as dangerous. One example is anastomoses, bizarre configurations of blood vessels in which fairly large arteries form short circuits with veins to create a futile cycle of circulating blood. These worthless blood vessels can actually pose a lethal threat if they grow large enough. Because they pointlessly receive a great deal of blood flow, even a minor injury to the engorged vessel can result in a massive loss of blood very quickly.
Though many are innocuous, anastomoses do not resolve on their own. An anastomosis that is actively growing must be removed before the mass poses serious health risks. Some of the most dangerous anastomoses form branches and eventually become tangled webs of interwoven vessels. In previous eras, these would have occasionally been fatal and quite often debilitating. Anastomoses, if left alone, tend to grow larger over time, creating an ever-swelling mass filled with stagnant blood. As such, they are usually removed with surgery or destroyed with radiation when they are very small. This correction, however, gets more dangerous the larger the mass grows because the sliced vessels will spew large amounts of blood before clotting can stop it.
An anastomosis, which shunts blood from an artery directly to a vein without passing through a capillary bed. This leaves the surrounding tissue devoid of oxygen, which can cause the anastomosis to grow in a runaway cycle.
Once these insidious structures form, they often end up in a runaway cycle of growth. This is because the tissue surrounding the pointless vessels paradoxically gets starved for oxygen-rich blood. Unlike normal arteries, which convey blood from the heart and branch into gas-exchanging capillaries that transport the precious oxygen to the body’s various tissues and organs, anastomosed arteries simply branch directly into another type of blood vessel: veins, which return the blood to the heart. Because anastomoses skip the capillary step, the tissue around them actually becomes oxygen-depleted, a condition called hypoxia, despite the fact that enormous amounts of blood are effectively passing through these tissues every second. In response, the hypoxic cells secrete a hormone that promotes the further growth of vessels in the anastomosis. The vessel gets larger; it may even form branches, and then even more tissue becomes hypoxic, and the cycle continues.
As with so many developmental defects, no one really has any idea how or why anastomoses form; they just do. This is more poor programming in our developmental genes and tissue architecture—basically, the untied-shoelace situation.
Coda: The Beast That Stalks Us All
Although many people have no allergies, will never have a stroke, and will escape the horror of an autoimmune disease, cancer is the beast that stalks us all. There is basically a 100 percent chance that, if you live long enough, you will get cancer. It will catch up with you eventually, provided you don’t die of something else.
Rates of cancer in the human population are skyrocketing. This is largely (though not solely) a function of people simply not dying of other things and thus living long enough to get cancer. Furthermore, all species of multicellular animals are subject to cancer. Humans are not unique in this. We get cancer at higher rates than some animals but at lower rates than others.
There is nothing about cancer that makes humans special, in other words, except that we now live so long that we develop it more than we used to. So why mention it at all? Why not skip over it, like atherosclerosis?
Because cancer is the ultimate bug-and-feature of nature. You cannot have sexual reproduction, DNA, and cellular life without also having cancer. Its very ubiquity, in fact, points to its extremity as a flaw of nature—a design defect that affects not only humans but many other living things as well.
Like autoimmune disease, cancer is a product of our cells. It happens when cells get confused regarding their own code of conduct and begin to grow and multiply out of control. The resulting clump of deprogrammed cells, in the case of solid tumors, loses its normal function and strangles the organ in which it appears. In the case of blood cancers—leukemias and lymphomas—the cancer cells crowd out the blood cells and the bone-marrow machinery to make more of themselves. In either cancer type, the cancerous cells usually spread to other tissues and take them over until the body is too crippled to continue. Thus, cancer is essentially a disease of cell-growth control.
Most of the cells of the body are capable of growing, dividing, and multiplying if and when needed. Some cells are almost always growing, like the ones in your skin, intestines, and bone marrow. Some basically never divide, like neurons and muscle cells. And some are somewhere in the middle—not always dividing but capable of doing so during wound healing or tissue maintenance. Cells must thus regulate their own proliferation. They should multiply when needed but stop when it’s time to. Cancer begins when a cell ignores the rules and continues to grow incessantly. In this sense, the disease is the corruption of our own cells; it causes them to take on a life of their own, abandoning their proper posts and dedicating themselves solely to their own growth and proliferation.
I was once seated on an airplane next to a Benedictine monk named Father Gregory Mohrman. During our conversation, I mentioned that I was returning home from a conference on cancer research. A very learned man, he was fascinated by this and asked many questions about my research and the nature of cancer itself. He then launched into an eloquent monologue regarding his thoughts on cancer, which I attempt to paraphrase here:
It seems to me that cancer is the ultimate biological manifestation of the devil. Cancer is not the result of a bacterial or viral attack, and it’s not that our bodies become damaged by some outside force. It’s us. Our own cells, as if seduced by some evil force, forget their proper place in our bodies and begin to live solely for themselves. They become the embodiment of selfishness, taking everything for themselves, sparing nothing for the rest. Never satisfied, they grow more and more and spread to other areas to continue growing and taking and killing. The only way we know to fight these corrupted cells makes us very sick because in attacking the cancer, we attack ourselves. There is no other way to fight the demon that has taken over our very flesh. This is why I have always held oncologists and cancer researchers in the highest regard. You are dedicated to the fight against evil.
The monk’s monologue left me breathless, and I have never forgotten it. Ironically, the opening paragraph of any article or text on cancer will often say the very same thing as his poetic yet supremely concise description, although with more clinical—and less interesting—wording. Cancer is indeed the result of nature’s poor design—a being’s own cells malfunctioning to the point of killing the entire organism. (A notable exception to this is the human papillomavirus, HPV, which can cause cervical cancer. Only a small minority of cancer cases are caused by viruses.)
There are two reasons why cancer is so stubborn. First, as Father Mohrman points out, cancer is not a foreign invader; it is our own cells gone wrong, and so drugs that fight cancer cells while sparing normal cells are hard to come by. Second, cancer is progressive—and usually aggressively so. Cancer cells are constantly mutating, which means that it is not the same disease over time; rather, it grows, morphs, invades, and ultimately spreads all over the body. A treatment that works at first will fail eventually. If a tumor contains ten million cells and doctors kill 99.9 percent
of them with radiation and chemotherapy, there are still plenty left to regrow the tumor—and it will be even more aggressive as well as resistant to whatever was used to shrink it originally.
What causes the body’s cells to begin growing uncontrollably? It turns out that nearly every cell in the body is subject to occasional mutations, which are random changes to the DNA sequence. Some of these are caused by toxins that we are bombarded with in our environment, but the majority of them are due to mistakes made when cells copy their DNA. With billions of cell divisions taking place daily, they make tens of thousands of errors every day.
This is how most cancer begins. With thousands of permanent mutations occurring every single day, occasionally one of them will hit a gene that nudges a cell away from its proper proliferation control and toward a cancer-like state. Mutations are random. There is nothing very special about so-called cancer genes that make them more susceptible to mutation. Most mutated genes don’t drive a cell toward cancer. Some do, however, and when those cancer mutations occur, the cell begins to grow in an uncontrolled fashion.
When this happens, the principles of evolution by natural selection take hold. If a mutated cell grows a little faster than its neighbors, its offspring will outnumber the offspring of its neighbors. The faster growth rate also accelerates mutations, since there is more DNA copying going on and thus more chances for additional errors. Most of those errors will have no effect, but occasionally, randomly, a mutation will occur that drives the cell faster still. That cell will then produce progeny even faster, and its offspring will outnumber the others yet again. Cancer is the result of successive waves of mutation, competition, and natural selection, several of which occur before the tumor is even large enough to be noticed.
Because it is both a bug and a feature of cell division, cancer is largely thought to be an inevitable fact of life for all multicellular organisms. As soon as living things were made of more than just a single cell, the problem of coordinating the proliferation of cells began. Cell division—and the DNA copying that goes with it—is a dangerous game. The more you play, the more likely you’ll eventually lose. Unless the human body somehow acquires the ability to flawlessly copy its own DNA—a biological pipe dream if ever there was one—if people live long enough, cancer will strike them at some point in their lives.
The grim irony is that cancer is, in a sense, a necessary byproduct of an essential part of life. Everything great that evolution ever brought was due to mutation. Random copying errors introduce variety and innovation. From an evolutionary perspective, mutations provide genetic diversity, which is good for the long-term survival of a lineage. Mutations in general are thus the ultimate feature/bug system.
Therefore, evolution has struck an uneasy balance with cancer. Mutations cause cancer, which kills individuals, but it also brings diversity and innovation, which is good for the population. Certain species, such as humans and elephants, spend years maturing before they can reproduce, so they must aggressively protect themselves from cancer, lest they succumb before they can have offspring. Shorter-lived species, such as mice and rabbits, can tolerate higher mutation rates and lazier anticancer defenses. True, cancer will eventually get us all, but that is the compromise. Evolution cares little about the individuals who will die of cancer. This is a sacrifice worth making for the diversity that comes from mutations.
As Lewis Thomas put it, “The capacity to blunder slightly is the real marvel of DNA. Without this special attribute, we would still be anaerobic bacteria, and there would be no music.”
6
A Species of Suckers
Why the human brain can comprehend only very small numbers; why we are so easily tricked by optical illusions; why our thoughts, behaviors, and memories are so frequently wrong; why evolution rewards adolescents, especially males, for doing foolish things; and more
In a book about human weaknesses, it might seem odd to find a chapter about the brain. After all, the human brain is by far the most powerful cognitive machine on the planet. Sure, computers can now beat us at chess and go. But in lots of other regards, we still have a major leg up on machines—even those whose only purpose is to think.
The advancement of the human brain beyond that of our closest relatives over the past seven million years has been truly exponential. Our brains are three times larger than those of chimps, but that doesn’t really capture the difference between us because almost all of the growth that the human brain has experienced has been in a few key areas, especially the neocortex, where advanced reasoning takes place. Our advanced processing centers are massively larger and more interconnected than those of any other species. Even modern supercomputers cannot compare to the fast and nimble capabilities of the human brain.
The beauty of the brain is not just in its raw computational power but also in its ability to self-train. Sure, we humans in the developed world subject ourselves to extensive formal education these days, but the most intense and impressive learning takes place outside the classroom. Our species’ acquisition of language, a skill far more profound and nuanced than anything we’ll ever learn in school, happens naturally and almost effortlessly and is driven purely by the brain’s remarkable ability to collect information, synthesize it, and incorporate it into its own programming. Advances in machine learning come nowhere near this level of achievement. Anyone who is reasonably bilingual can easily see just how much smarter the human brain is than a computer by playing around with Google Translate, possibly the most sophisticated translation program publicly available. After just a few months of lessons, the human brain can translate between languages better than the fastest computers can.
But the brain isn’t perfect. The human brain is easily confused, tricked, and distracted. There are certain rather low-level skills that it struggles to master. It makes embarrassing blunders even within its otherwise impressive skill set and is beset by bizarre cognitive biases and prejudices that handicap it as it tries—and sometimes fails—to make sense of a complex world. It is overly sensitive to certain inputs and blind to others. And it rigidly adheres to outdated dogmas and superstitions that even the most elementary logic refutes (I’m looking at you, astrology), while a single anecdote can shape its entire worldview on an issue.
While some of the brain’s limitations are the result of pure accidents—the unexplained misfiring of a computational instrument with finite capabilities—others are the direct result of how the brain is wired. The power and flexibility of our species’ brains evolved while our ancestors were living very differently than modern humans are now. For almost all of the past twenty million years, our species’ lineage was that of just another ape. We humans reached our current anatomical dimensions only about two hundred thousand years ago and began the shift toward modern ways of living only about sixty-five thousand years ago. Our species hasn’t undergone much genetic change since settling down into civilized life, and so our bodies and brains are built to make sense of a very different world. Our mental abilities—now used for such things as philosophy, engineering, and poetry—evolved for totally different purposes.
The period most crucial to human evolution was the Pleistocene epoch, which began about 2.6 million years ago and lasted until the end of the last ice age, around twelve thousand years ago, a point in time sometimes called the dawn of civilization. By the end of the Pleistocene, humans had spread around the globe, most of the major racial groups were established, agriculture was being developed in many places simultaneously, and the gene pool was little different than it is now.
In other words, human bodies and brains have not changed much in the past twelve thousand years. This is a kind way of saying that we are not adapted to this life. We are adapted to Pleistocene life. And perhaps nowhere is this clearer than in the way we perceive the world around us.
Fill in the Blanks
Optical illusions are a staple of fun houses, museums, circuses, magic shows, coffee-table books, and, of course, the Internet. These visual tr
icks dazzle us because they leave us with a sense of cognitive dissonance. We know that things aren’t quite right as our brains unsuccessfully continue to try to find a solution to the problem. This can be fun but dizzying. Most people get uncomfortable if their brains are confused for too long.
There are dozens of types of optical illusions—physically impossible objects (like a fork that has either three or four prongs depending on which side you look at), perfectly straight lines that look bent or broken, the appearance of depth or movement in a static two-dimensional picture, even spots or images that appear and disappear based on how you move your eyes across them. Each has a slightly different mechanistic explanation, often centering on the theme of our brains’ “filling in the blanks” when information is missing (or misleading) in order to create a complete, if inaccurate, picture. The senses relay very raw, unprocessed, nearly unintelligible information, and the brain must construct this mishmash into a coherent picture. It’s not unlike the signal that goes to a computer monitor. It’s nothing but a rush of electrons that ping out the 1s and 0s of binary code, and yet the video card sorts out the blur and creates a highly organized image.
Unlike a computer monitor, however, the human brain has the fascinating ability to extrapolate from the information it has. This happens unconsciously. Most of the time, it comes in handy. For example, we are highly attuned to faces. Our species has a spectacular diversity of face shapes and structures, and the human brain picks up on these subtle differences instantaneously. While most people struggle with names, the majority never forget a face, and many of us can recognize friends from a single feature, such as an eye or a mouth. This is because faces were key to sociality during the long Pleistocene time before language developed. Humans used faces to recognize one another and communicated with their expressions. This has led to our amusing tendency to see faces in inanimate objects.
Human Errors Page 16
