We don’t know much about how the human body functions.
For someone who just casually browses the subject of anatomy, it would seem that we have the human body all figured out. Not really…
The lungs are there to provide oxygen, the heart is there to pump blood, and the nails are there to scratch people when they’re being annoying. All is known. Pick up your average textbook on human anatomy, and the overall impression that one gets is that every square millimetre of the body has been accounted for, from every angle: structure, function, development, moment-by-moment activity…you name it, we know it.
But how true is that really? Well, upon closer inspection, it turns out that there’s a ton that we don’t know about the human body. Some of the unknowns are more obvious, like ‘what is consciousness?’ (stay tuned), while other unknowns are quite unexpected, like why exactly do we sleep every night? The implicit belief that we know all there is to know about the human body can make us blind to just how complex the stuff that we’re made up of really is, and can lead us astray when we try to tackle a complex issue like consciousness. So, this post aims to be a sobering reminder of just how much we don’t know about our own bodies in general, which will hopefully provide a sense of perspective for when we delve into the human brain and consciousness in the next posts.
The unknowns about the human body span at every level, and from every angle you look at:
1. Subcellular
We have no idea what over 30% of the proteins in the human body do, even though they are constructed by our own cells. That’s over 2000 proteins that have an unknown function. We can tell that they get coded because we’ve sequenced the DNA that makes them. But what exactly do these protein molecules do? No idea.
2. Cellular
By the latest estimates, the human body is thought to comprise of 37.2 trillion human cells. Saying that’s a lot is an understatement, so no wonder there are a lot of unknowns, but we rarely hear about them. Let’s see some documented examples:
For some cells that we’ve discovered exist in the human body, we have no idea what their function is. Take oxyphil cells — cells that appear in the parathyroid glands, which are found in the neck. These cells appear at the onset of puberty, and we have no idea what they do.
We keep discovering new types of human cells, even after hundreds of years of microscopic study. In the 1990s, we’ve discovered that the eye has a third type of photoreceptor cell apart from the often mentioned rods and cones- the intrinsically photosensitive retinal ganglion cell. Needless to say, people were surprised at the finding, and even die hard scientists were complete deniers, since many believed that after 150 years of careful microscopic study of the eye, such a thing couldn’t be missed. Well, it was missed, and this is exactly the kind that makes for a reminder of how little we do know about our own bodies. Another example is the discovery of the ‘rosehip neurons’ in 2018, a new type of brain cell that so far had only been found in the human brain — arguably the most studied of all human organs — but we’ll delve more deeply into the unknowns related to the human brain in the next post.
These are just two examples, but there are many more: From the discovery of new types of white blood cells in 2017, to new types of immune cells found in human breast ducts in 2020. Also in 2020, scientists discovered a new type of taste bud in the mouse tongue. As opposed to all of the other taste buds, these respond to all four primary tastes, instead of just one: Sweet, sour, bitter and umami. It wouldn’t be surprising if these new taste cells would come up in humans as well.
And then there are all of the unknowns related to the non-human cells found in the human body. In fact, 67% of all cells in the human body are bacterial cells. This is ON TOP of the 37.2 trillion human cells mention prior. The total estimated weight of bacterial cells is thought to be about 0.2 kg, so only a fraction of the body’s total weight. Nevertheless, one fascinating metastudy analysed data about bacteria gathered from human bodies around the world found a total of 4000 different species of bacterial cells, and 70% of those species have never been cultured, so we have no idea what they do. We just know that these species exist in human bodies because we’ve sequenced their DNA from human tissue. And then there’s all the species of fungi and viruses living in the human body that we know even less of...
3. Tissue & Organs
You would think that we would’ve figured out what the organs of the body are a long time ago. But then in 2018, researchers came out with information on a structure in the body that could be considered a new bodily organ. This is called the interstitium — an interconnected bundle of fluid-filled spaces that line up much of our innards. Scientists are still debating whether to confer the interstitium the coveted title of an independent organ, kind of like how astronomers still debate whether Pluto is a planet or not. The inner universe, it turns out, is as complicated to map as the one outside of us.
Related to organs, even after over a hundred years of careful study, we’re still discovering new brain areas, like The Endorestiform Nucleus found in 2018, whose function has not yet been determined, but which is not found in other mammals as far as we know.
And then we have no idea how certain tissues manage to do what they do. For example, the liver is the only organ in the human body able to regrow — if you cut as much of 2/3 of it, it will grow back in time. But how exactly do liver cells know how to grow, or when to stop growing before they overrun the space dedicated to other organs? We have no idea.
4. Bodily functions
What do orgasms, sleep, dreaming and laughing have in common? If you thought ‘they can all make you feel good’, good for you, you positive soul! But the other thing that they have in common is that they are not completely understood. Most often, some of the processes that underscore one bodily function or another is grasped, while a lot more remains unknown, which is why diseases related to these bodily functions can completely baffle doctors. Take postorgasmic illness syndrome, in which people get sick immediately after ejaculation. Some may get debilitating pains, others intense fatigue (not the good kind) or feverish states. What causes this syndrome? No idea, which links to the fact that there is much left to learn about orgasms in general.
5. Birth and development
If you’ve ever wondered why there are no artificial wombs in the world yet, a la Frank Herbert’s Axlotl tanks, it’s because giving birth is a miracle, and I mean literally, considering the unknowns. How do germ cells — the original sperm and egg cell — know to proliferate and differentiate into so many different types, to the point where they form a fully grown human? Like Mirna Marinic, a postdoc at the University of Chicago Department of Organismal Biology and Anatomy, said:
“Pregnancy is such an everyday event — none of us would be here without it — and yet, so many aspects of this process remain puzzling.”
6. Disease
And then, there are diseases, the first place where we would apply our knowledge would we know EVERYTHING about the human body. Let’s look at a couple of them:
Cancer. The more we look into cancer cells, the more dastardly they turn out to be. When they form tumours, they can hide themselves to appear like lymph tissue so that the body’s defences do not wipe them out. They can change shape to escape detection from immune cells. They even hide from chemotherapy by concealing themselves in bone and in other ways. They signal other cells to do their dirty work, and so on. And as for the cause of cancer, there is no obvious one for many of them.
What about asthma? People normally believe that asthma is caused by living in a place with bad air, but that is not always the case. As Bill Bryson puts it in his book The Body — A Guide for Occupants:
In clean Hong Kong asthma rates are 15 percent, while in heavily polluted Guangzhou they are just 3 percent, exactly the opposite of what one would expect.
In reality, the cause of asthma has not been determined.
Many more diseases with unknown causes are in existence, from skin diseases to muscle diseases to neurobiological diseases, the list is huge (Here are a couple of lists: 1, 2). And these diseases point to the fact that the places in the body where they emerge are not fully understood, since if they were, those diseases would be treatable as well.
7. Conclusion
These are just some of the examples that show just how incredibly complex the human body is, and how much there’s still left to discover. That isn’t to say that we haven’t discovered a great deal already — a large number of very intelligent people have been working tirelessly over centuries to get to the level of knowledge that we currently have of the human body. What the information outlined in this post indicates, however, is that we still have a long way to go before we can confidently say that ‘we know it all’.
So what’s the reason behind all of these unknowns? At its core, the answer is simple: It is incredibly difficult to peer into the living body in real time, much more difficult than is implied in popular science. We do have tools that allow us to do some general analysis of what takes place within the body, from endoscopes to CT scans to X-rays, but to look at the microscopic or nanoscale structure of human tissue while it is still in the living body is impossible in all but special cases. The microscopic structure can only be looked at when we perform biopsies — that is, when we get a sample of tissue; Or when we kill off the organism and run DNA analysis on its tissue; Or when we design organisms specifically for microscopic study, as is the case with optogenetics, where light can be used to activate specific neurons in the brains of genetically engineered animals. These methods, obviously, come with their own set of limitations, and are not the same as knowing what takes place in the unadulterated human body at the microscopic level in real-time, which leads to all of the unknowns mentioned, and many more medical ‘mysteries’. Understanding this fact puts our knowledge of the human body in a totally new light.
Hopefully, this sets the stage for when we talk about the human brain, which has been called the most complex piece of matter in the universe. In the next posts, we will delve deep into just what that means.
