Our bodies, comprised of approximately 30 trillion cells, undergo a continuous daily renewal process, with about 1% of cells being replaced. However, this regeneration is not flawless. The DNA in newly formed cells frequently contains numerous errors, known as mutations. It’s estimated that trillions of new mutations can occur within a single body each day.
“You are a slightly different genetic version of yourself today from yesterday, and will be different yet again tomorrow,” remarks Roxanne Khamsi in her book, Beyond Inheritance.
These genetic alterations span a wide spectrum, from minor changes in a single DNA base pair to the complete loss of an entire chromosome, such as the X or Y chromosome. While many mutations are eliminated as cells naturally die, a significant number are inherited, accumulating over the lifespan. Consequently, by the end of one’s life, an individual’s cells may have amassed thousands of mutations.
Many are aware that such mutations can lead to uncontrolled cell growth, resulting in cancer. Nonetheless, Khamsi elucidates that non-cancerous mutations are responsible for a diverse array of health issues.
Visible Manifestations of Cellular Change
In some instances, the consequences of these mutations are outwardly visible. For example, the appearance of purple “birthmarks” stems from mutations occurring early in development that impact blood vessels, among other tissues. Similarly, mutations within skin cells can alter the production of melatonin, leading to variations in skin pigmentation. These differing shades often follow specific developmental patterns, known as Blaschko’s lines.
This phenomenon of cellular variation is not confined to specific tissues; it occurs throughout the body and at all developmental stages. In essence, every individual is a mosaic, composed of cell populations that exhibit genetic differences. These inherent cellular discrepancies can occasionally bestow a competitive advantage upon particular cells.
Cellular Evolution and Health Risks
Consider the example of blood. When blood stem cells divide, one daughter cell remains a stem cell, while the other differentiates into a blood cell. Under conditions of uniform stem cell division rates, all descendant cells would theoretically be identical. However, mutant cells that replicate at an accelerated pace generate a greater number of descendants. Over time, this can result in a significant portion of an individual’s blood being derived from these mutated cells. This situation is observed in at least ten percent of individuals by the age of 70. The implications are concerning, as mutant blood cells have been linked to a doubling of the risk for heart attacks and strokes.
At its core, this dynamic represents an internal evolutionary struggle among our cells. Those cells that acquire even a minor growth advantage gradually gain dominance. Khamsi notes, surprisingly, that many 19th-century thinkers, following Darwin’s work, recognized that evolutionary forces were also operative within the human body. However, this concept was largely neglected after 1900 with the advent of modern genetics.
Emerging Clonal Disorders and Detection Challenges
A growing number of conditions are now being identified as “clonal disorders.” These include certain forms of endometriosis, where uterine cells migrate and grow on other organs. The extent of this is likely broader, as researchers are likely only beginning to understand the full scope. Some types of mutations remain difficult to detect, and many organs are challenging to study directly, making the sampling of heart or brain cells, for instance, impractical.
The Double-Edged Sword of Mutations
However, the news is not entirely negative. One of the most startling aspects discussed in the book is how new mutations can sometimes successfully counteract inherited medical conditions. There is even evidence of liver cells adapting and evolving mechanisms to manage conditions like fatty liver disease. Despite these beneficial occurrences, helpful mutations represent an exception rather than the norm.
While the overall message is significant, the presentation could be improved. The author tends to include extraneous personal details about individuals and locations that do not directly contribute to the factual content of the work, which can be distracting for the reader.
Nonetheless, the book’s central theme holds considerable importance. It effectively synthesizes diverse research from various scientific disciplines, presenting a compelling picture that warrants broad awareness, particularly among those in the healthcare field. The core insight is that our bodies are populated by constantly changing and often rebellious cells, engaging in competition and sometimes prioritizing their own survival over our well-being, even when they do not progress to full cancerous transformation.
“By letting go of the antiquated idea that every cell has the same exact DNA and embracing the messier reality that each of our cells has a slightly different genetic code, we can usher in a whole new era of medicine,” Khamsi states.
While the concept of a completely “new era” of medicine may be ambitious, the implications are undeniably profound. Khamsi’s work, in essence, describes how multicellularity within an individual gradually deteriorates as cells become more divergent and inherently self-serving. This resonates with the notion that “Things fall apart; the centre cannot hold.”
Mutation as a Potential Driver of Aging
This process may also be a fundamental cause of aging, as Khamsi explores. For instance, several conditions characterized by premature aging involve defects in DNA repair mechanisms, leading to an accelerated accumulation of mutations. Furthermore, species with longer lifespans tend to accumulate mutations at a slower rate compared to those with shorter lifespans.
Regardless of whether the build-up of selfish mutations is the primary driver of aging or merely a contributing factor, it suggests that the complete cessation of aging is an unrealistic prospect. While interventions like certain drugs might slow mutation accumulation, and gene editing technologies could potentially correct some errors, these efforts are unlikely to offer a permanent solution. The inherent mutational processes appear too pervasive.
Even with advancements such as body transplantation, the brain’s eventual decline remains a certainty. Studies of individuals who died in accidents have revealed approximately 1,500 mutations in each neuron analyzed. The sheer volume of ongoing mutations fundamentally limits the ability to indefinitely forestall this biological process.
Humanity’s Unique Genetic Destiny and the Future of Lifespan
While the biological inclination to mutate cannot be halted after conception, Khamsi observes that “humans are the first living creatures that seek to shape their genetic destinies.” However, she does not pursue the logical implication that a radical redesign of the human genome, aimed at significantly reducing the mutation rate, could be the sole pathway to dramatically extending human lifespans.
Such an endeavor might become technically feasible. Yet, describing the outcome as an extension of “human” lifespan becomes problematic. To mutate is an inherent human characteristic. If such genetic modifications were implemented, the resulting beings might fundamentally differ from what we currently define as human.
Related Works on Inheritance and Biological Change
Power, Sex, Suicide: Mitochondria and the Meaning of Life by Nick Lane
Nick Lane’s work explores how human cells’ energy-generating mitochondria, originally independent bacteria, evolved into an essential component of complex life through a symbiotic union. He details how their distinct origins continue to influence our destinies in multifaceted ways.
Mutants: On the Form, Varieties and Errors of the Human Body by Armand Marie Leroi
Armand Marie Leroi posits that all individuals are, in a sense, mutants. He illustrates this with examples such as cyclopia in newborns, a condition that, while often fatal, offers valuable insights into human developmental processes.
Old Man’s War by John Scalzi
John Scalzi’s science-fiction novel, Old Man’s War, offers an imaginative exploration of aging and its potential transcendence. The book is highly recommended for its engaging narrative, with sequels that maintain or even enhance its quality.