Every human is born with approximately 100 genetic mutations, unique from their parents. As you have children, half of these mutations are passed down, coupled with new mutations from the next generation. This raises an important question: Are harmful mutations accumulating in humans, leading to a decline in both physical and mental fitness?

Some experts, like geneticist Michael Lynch, suggest that we could see a significant decline in human physical fitness over the next few centuries in industrialized societies. In a 2010 study, various countries, including the UK and Australia, reported declines in IQ, suggesting we might be witnessing a direct consequence of these accumulating mutations.

Historically, the concept of human degeneration spurred highly unethical eugenics policies in the 20th century. While early proponents fabricated stories to justify their views, modern genomic sequencing allows us to directly analyze mutations and understand their implications.

Research indicates that humans possess a relatively high mutation rate compared to many other species. The male reproductive system, responsible for producing sperm continuously from stem cells, plays a vital role in this process. As men can father children for extended periods, mutations may accumulate over generations more than in short-lived species.

While most of our 100 additional mutations have little impact due to the prevalence of ‘junk’ DNA, some can lead to harmful effects. These mutations can occur within protein-coding genes or regulatory sequences, potentially altering gene function.

While severe mutations can be life-threatening, others with minor negative effects can persist through generations. So, what prevents a continuous buildup of harmful mutations in populations?

Traditional genetic theories posit that offspring with significantly damaging mutations are less likely to survive and reproduce, stabilizing the ‘genetic load’ of harmful mutations within populations. However, with evolving health care and conditions in high-income countries, natural selection may be weakening.

Lynch proposes that relaxed natural selection is contributing to the accumulation of harmful mutations, predicting a reduction in human fitness by at least 1% per generation, and perhaps even up to 5%.

Nevertheless, some studies upon which Lynch’s predictions are based involved non-mammalian species. Peter Keatley and his team at the University of Edinburgh explored mutation accumulation in mammals, breeding 55 strains of mice over 21 generations under relaxed selection conditions. Their findings, published in 2024, suggest that the fitness loss in humans per generation may equate to less than 0.4%.

It’s worth noting that natural selection remains effective, as a considerable percentage of pregnancies end in miscarriage. According to Joanna Maskell from the University of Arizona, “There’s always a choice.”

Is Losing Physical Strength Necessarily a Negative Thing?

Moreover, fitness, in an evolutionary context, isn’t always advantageous. Genetic mutations providing resistance to infectious diseases or malnutrition may have adverse effects when those threats are minimal or negligible. For instance, a mutation providing malaria resistance can manifest in sickle cell disease when malaria is absent.

In the larger scheme of evolution, organisms like bacteria can quickly eliminate harmful mutations due to their smaller genomes and large population sizes. However, Maskell notes that this rapid elimination isn’t feasible for humans.

“Our genomes are cluttered with various parasitic elements,” she states. “The influx of harmful mutations surpasses our capacity for removal, yet we possess mechanisms to compensate for them.”

Instead of individually cleansing genetic disadvantages, organisms have evolved a ‘sewage system’ to manage multiple issues simultaneously. This evolutionary process suggests that even rare beneficial mutations with substantial effects can counterbalance numerous slightly detrimental mutations.

This perspective is profound; harmful mutations can paradoxically drive complexity by creating issues that require the evolution of advanced solutions. For example, when a mutation introduces junk DNA into a gene, cellular systems have evolved to excise this extraneous material from the RNA copy.

Interestingly, simulations conducted by her team indicate that as mutation rates rise, beneficial mutations accumulate more rapidly than harmful ones.

“We’re effectively enhancing our waste management system at a faster rate than we create disruptions,” Maskell comments. “Surprisingly, the mathematical outcomes were counterintuitive.”

If these findings hold true, then the high mutation rates in humans may not present the alarming issue many biologists fear. The correlation between declining IQ and mutation may be coincidental. The scientific inquiry continues, yet there’s little cause for alarm regarding human degeneration.

Meanwhile, there are pressing global issues that warrant our attention, such as climate change, which Maseru suggests should be our primary concern instead. I wholeheartedly concur.