We Are Barely Aware of What's Happening in Our Own Bodies

Interview with Prof. Nathan Lents, Author of Human Errors: A Panorama of Our Glitches, From Pointless Bones to Broken Genes

Your book opens with the incredible epigraph "Now, there's a topic you know a lot about!" – My mother upon learning I was writing a book about human flaws. Humor aside, as you were writing "Human Errors", was there a specific flaw of the human body – or of your own – that you found your thoughts kept circling back to?

The first big flaw that I learned about back in college was our broken GULO gene, which requires us to obtain vitamin C from our diet, rather than just making it for ourselves in our livers, like most animals do. This completely shocked me, because how many humans have died of scurvy, long before anyone had any idea why? But the story gets even more shocking the more you think about it because, since scurvy is lethal, how did this terrible mutation persist instead of being eliminated by natural selection? The answer is because our ancestors lived in environments that happened to have vitamin C abundantly in the available food - citrus fruit - so the loss of GULO had no effect on them, but any time these primates tried to migrate away from tropical rainforests, they suffered from scurvy. All because of some terrible bad luck millions of years ago! 

Which anatomical "design flaw" in humans do you think has the greatest impact on our daily lives, yet remains largely unnoticed?

An example of a tragic flaw that we didn't even know about until recently is our loss of the gene that encodes a protein called theta defensin. This is a small protein that helps animal immune systems fight off retroviruses. Without this protein, we are more vulnerable to this kind of virus, a family that includes HIV. Had our ancestors not lost theta defensin, it's quite possible that the AIDS pandemic might never have occurred. 

Many people claim that nothing given to us by evolution is truly unnecessary – that it's simply not yet the time for some traits to reveal their purpose. Do you see any truth in that idea?

In some cases, maybe, but in most cases, definitely not. The appendix is a good example of a vestigial structure that seemed to be only a flaw because it sometimes gets a life-threatening infection. We later learned that the appendix is often a reservoir of good intestinal bacteria useful for repopulating the colon following a bad case of diarrheal infection. So it does a serve an important purpose at certain times. So maybe it's not fair to call it a pure flaw, but please keep in mind that appendicitis is often lethal, and always  was prior to modern medicine. So for people who got an infected appendix, it's hard not to see this organ as a flaw, at least for them. 

If humans continue evolving for another million years, which of our current "errors" do you think evolution is most likely to correct – and which flaws might persist indefinitely?

The typical evolutionary force of natural selection doesn't really work on the human species in the usual way anymore because of technology, medicine, food production, etc. We don't really live or die based on how well our bodies work anymore. We are still evolving, but not really based on natural selective processes. So I don't think our flaws will be corrected by evolution, but I DO think that they'll get corrected by medical technology, gene editing, etc. I think within one generation, we will be fixing inborn genetic diseases, and maybe even from the germ line, which means they will be permanently removed from the population. 

You say that our bodies became so limited because we began solving life's challenges with our brains and our sociality rather than with physical abilities alone. Looking at the modern world, do you think we might be moving toward a kind of degradation – and are the widespread sedentary lifestyle and unhealthy eating habits just the tip of the iceberg of our problems?

Yes, it's very fair to say that many modern habits are not good for us, for our bodies, our minds, our relationships, our societies. At this point, these poor habits won't affect our genetics, so we could always move past them and start living more healthy lives and building more healthy societies... that is, if we ever develop the political will to do so. So most of the modern degradation is completely reversible, at least for now. 

You often say you're fascinated by how DNA encodes life. When you look at the structure of DNA, does it feel like a lucky coincidence of chemistry, or does it suggest deeper principles we don't yet understand?

Well in the game of molecular evolution, of course there is a lot of luck involved, some very improbable things had to happen in a precise sequence in order to build the complex molecules of life in a stable and consistent way. But, in the vast primordial oceans, there were trillions of test tubes running molecular experiments for hundreds of millions of years, so highly improbable things eventually do happen. If you have a pair of dice, it's incredibly unlikely to roll the same thing 20 times in a row, right? But if you get a billion tries, it will happen. That's how life emerged from a lifeless planet, from relentless chemical tinkering in a vast ocean over hundreds of millions of years. Even incredibly unlikely things will happen if you try enough times. 

You note that you chose the topic for this book because there are already plenty of books celebrating the efficiency and remarkable abilities of the human body. But if you had to point to just one thing – what is the most distinctive feature of humans that isn't a flaw, something evolution actually got impressively right?

I would say that the genes that orchestrate the developmental program that leads to the development of our massive and intricately interconnected cerebral cortex is our most impressive feature. Of course, other animals have brains, some of them with very large cortices, but ours is an order of magnitude larger, which means several orders of magnitude more interconnected. Just our cerebral cortex has 10-20 billion neurons, and something like 100 trillion connections. It's absolutely astonishing that this can be built with genetic instructions from just a few thousand genes. 

What's more astonishing – that the human body works as well as it does, or that it works at all despite all its shortcomings? And what is the single most mindblowing fact about how the human body functions?

I think it's absolutely amazing that a genome of just 20,000 protein-coding genes encodes something as complex as a human being. And it all operates more or less autonomously. My book explains what we can learn from some of more obvious shortcomings, but there is no denying that a whole lot of things work so smoothly that we're barely aware they even exist. The chemistry of life is endlessly fascinating!

Interview by Vladimir Tsankov