The Immortality Of Our DNA

My father-in-law isn’t young, but, at 76, and only having retired two years ago, he isn’t very old either. And he’s lived a healthy life, having never smoked, or drank alcohol, and been a life-long vegetarian. But all his healthy living couldn’t override his genes, and his hereditary haemochromatosis, a condition that caused iron overload in his liver and hepatocellular (liver) cancer.

Since my father-in-law’s cancer diagnosis I’ve been thinking about the inevitability of our mortality, the purpose of our existence, and the sheer number of things that can go wrong with our bodies. 

In a thought-provoking book, Human Errors, Nathan Lents, a professor of biology at The City University of New York, documents many of our human faults including our spines that seemingly haven’t yet properly adapted to an upright posture, the way our immune system attacks our own bodies, and our brain’s cognitive biases and memory flaws.  

Lents also discusses how, in evolutionary terms, such flaws may not matter in the grand scheme of things, as long as it doesn’t impede our ability to have children.

“One of the preconditions of evolution, perhaps the most important, is that a species must be able to reproduce,” Lents writes. “We all have an inborn drive to make more of ourselves. It’s the only way a species survives … we are hardwired to want to pass on our genes.”

Professor David Vaux, microbiologist and deputy director of the Walter and Eliza Hall Institute of Medical Research in Melbourne, agrees.

Deputy Director of the Walter and Eliza Hall Institute of Medical Research Professor David Vaux
Photo credit: The Walter and Eliza Hall Institute of Medical Research

“Really, we’re all just machines that carry around and propagate genes,” he told me. “We’re all the products of an unbroken line of genes that have been good enough to design our bodies to reproduce and produce us. Unbroken since the dawn of life over a billion years ago.”

Vaux points out that we only have a couple of cells that truly matter in evolutionary terms. “For multi-cell organisms, only one or two of our cells get to pass on and live to another generation. Our sperm cells and our egg cells,” he said. “So really ageing is just getting rid of the somatic cells and allowing the germ cells to hopefully go on to a new generation.”

This somewhat dystopian yet pragmatic concept has been with us for centuries according to scientist Mike McRae who has recently released Unwell, a book which provides historical context to the concept of disease.  

“In a time long before we knew that sperm carried the father’s contribution of genetic material, it was believed that something inside semen contained an expendable baby. Like a seed in a field, the baby was planted in a womb, which provided the necessary liquids and nourishments to make it bigger,” he writes. “One proponent of this ‘preformationist’ hypothesis, Nicolas Malebranche (a 17th-century French priest and scientist), speculated that all of Earth’s life forms were created at the same time many generations ago, and tucked away inside their ancestors like the world’s longest line of matryoshka dolls.”

Although this idea may seem absurd through 21st-century eyes, Vaux points out that some organisms have effectively been alive for millions of years. “Every single-cell organism alive today, every bacterium and every protozoa. None of its ancestors ever died,” he said. “So if you’re a single-cell organism, each cell, if it’s alive and well enough to divide in two to produce progeny, then it never died because it just divides in two.”

Given the evolutionary importance of having children, one might assume that our reproductive organs are able to operate at the peak of functionality. Not so, argues Lents. “We are some of the most inefficient reproducers in the animal world because we have errors and flaws throughout almost the entire reproductive process.” 

Nor is our DNA exempt from errors. The DNA in our cells stores hereditary information as a double helix code made up of four chemical nucleotides. Genes, of which there are about 25 thousand in the human body, are sequences of nucleotides, anywhere from a few hundred to two million base pairs long, that encode for functioning proteins.

As cells divide, each strand of DNA serves as a pattern for duplicating the sequence of bases so that the new cells will have an exact copy of the old DNA.

Given the complexity involved in DNA replication, Vaux believes that it is surprising that there are not more genetic mutations. “Every time one of our cells divides in two, it’s got to make a perfect copy of those six billion DNA letters. And remember that there’s a million cells that finish dividing in two every second,” he said. “The really amazing thing is we don’t develop cancers while we are still in our mother’s womb.”

Despite the incredible process of DNA replication, mistakes do occur. Lents points out many of these apparent errors in our genome, including “junk” DNA, the estimated at least 97 per cent of DNA that does not code for a protein. “There are vast expanses of our genomes – the entirety of the DNA we carry in each of our cells – that do not have any detectable function.”

Lents also talks about pseudogenes, evolutionary remnants of once functional genes that became mutated beyond repair millions of years ago. “Scientists estimate that the human genome contains the intact remnants of nearly twenty-thousand pseudogenes,” he writes. “That’s almost as many broken genes as functional ones.”

Just as compelling is his discussion of retroviruses (viruses that incorporate their genetic code into their host’s DNA). Although many retroviruses, such as HIV, are still tragically active, the majority appear to have been mutated out of existence, their only evidence being sequences of no longer coding but probable viral origin DNA present in our bodies. Lents estimates that eight per cent of our human DNA is comprised of such “viral graveyards”, being passed down generation after generation.

Other scientists have a more positive view of our genome, pointing out that there is much about DNA, whose double-helix structure was only discovered in the 1950s, that remains unknown.

“The term ‘junk DNA’ is pejorative and it seems to offer an explanation for something that we don’t understand,” genetic pathologist and Human Genetics Society of Australasia president Michael Buckley told me. “There is good evidence to think that some of that contains sequences that are important for telling a gene when to be expressed and which tissue to be expressed. So some of the so called ‘junk DNA’ is well known to be functional.”

Indeed, the concept of what is normal versus abnormal can, and often does, change over time. McCrae’s book documents multiple instances of “diseases” that have been debunked with our increasing knowledge. This infamous list includes hysteria; left-handedness; miasma; neurasthenia; and homosexuality (which was only completely removed from the Diagnostic and Statistical Manual of Mental Disorders in 1987).

McCrae adopts a sombre note when it comes to genetics, discussing the history of eugenics and the horrors that entailed, and urging caution regarding genome manipulation through future technology.

“There is no clear line between disease and desired. Nor should we pretend there is,” he writes. “Decisions to edit genes … shouldn’t be led by the impression that science can highlight what to cut and what to keep … What if, by excising genes that make an individual prone to depression or anxiety, we also deprive them of greater levels of sensitivity or creativity?”

By trying to eliminate certain traits or conditions that are viewed as unfavourable, McCrae warns that we may potentially weaken humanity.

“Humans thrived because our social brains, working in combination, could create a superorganism of tribes,” he writes. “It doesn’t matter if you can’t make babies or hunt mammoth if you can provide childcare, wisdom or social support. Fitness isn’t simply about an individual’s robust organs. Darwin’s idea of natural selection doesn’t fall apart when we look after our ill, our disabled and our elderly. It’s strengthened.”

Lents agrees that these factors likely played a significant role in why Homo sapiens, even though we weren’t the strongest species, or the fastest species, and we certainly weren’t the best breeders, still managed to become the dominant species.

“In a highly social group, each member pulls his or her weight in a different way,” he writes.

Of course, there is more to life than merely having children, or helping to raise other people’s children, though as we reach the ends of our lives, many do find comfort in this.

Kathryn Mannix, a palliative care specialist in the United Kingdom, discusses the concept of legacy in her new book With The End In Mind: Dying, Death and Wisdom in an Age of Denial.

“What legacy have you already generated? You may have given birth to children or to innovative ideas; you may have taught a grandchild how to use a screwdriver or how to see pictures in the clouds; you may have founded a major company or grown a garden. You may have borne sorrow with courage that inspired other people, or quietly supported another in their time of need.”

Over the weekend I was building Lego with my daughter, and as she concentrated on building a turret for her princess castle, I caught an expression on her seven-year-old face that I’ve been seeing a lot lately.

I saw her lips curve sideways, her right cheek lower than her left, an expression that reminds me of her grandpa when he’s thinking.  

And in that moment, I realised that once my father-in-law is gone he will live on in the unbroken line of genes now carried by my daughter.       

Suvi Mahonen is a Surfers Paradise-based journalist. Her work appears in The Australian, the Australian QuarterlyMamamia and other health and lifestyle publications. Follow her on FacebookYouTube and online art-selling platform Redbubble.

One Reply to “The Immortality Of Our DNA”

Leave a Reply

Your email address will not be published. Required fields are marked *