The Betrayal of the Good Genes That Made Us Human

Last revised: June 30, 2024

Genetic traits that once favored the survival of early humans have, in the modern era, become risk factors for obesity, heart disease, and depression. Drawing on Dr. Goldman's research, this article explains the trade-offs of evolution and the outlook for genetic medicine.

Humankind Has Walked a Long Road

We Homo sapiens carry roughly 300,000 years of evolutionary history. For early humans, every day was a fight for survival. Without hunting, there was no food, and people were constantly exposed to threats such as fierce animals and harsh natural environments. Only those who survived under these extreme conditions—those with superior physical strength, endurance, and adaptability to their environment—passed on their genes, and those advantageous traits were carried down through the generations [ref:1].

But what if the genetic traits that were once essential for survival have become "weaknesses" for modern humans? Dr. Goldman's book "Too Much of a Good Thing" explores precisely this paradoxical theme. The book reveals the striking fact that the physical and psychological traits early humans needed for a hunter-gatherer lifestyle have, in today's society of abundance, instead become risk factors for disease [ref:2]. This phenomenon is known in the field of evolutionary medicine as the "mismatch hypothesis," and it has drawn attention from researchers around the world [ref:3].

Humans Evolved in an Era of Scarce Food and Water

For early hunter-gatherers, it was only natural to eat everything available whenever food could be found. In an environment where it was uncertain when the next meal would come, eating as much as possible and storing the energy in the body was an extremely rational survival strategy. As a result, the human body developed mechanisms to efficiently store energy as body fat. Specifically, hormones that prevent weight loss (such as leptin and insulin) were finely tuned through the process of evolution, building a system prepared for famine [ref:4].

Furthermore, early humans needed to sweat heavily to regulate their body temperature during long hunts under the blazing sun. To replenish the sodium (salt) lost through sweat, humans developed a taste preference for salt. This "craving for salt" remains deeply ingrained in us today, and many people routinely consume far more salt than they need. The World Health Organization (WHO) recommends a daily salt intake of less than 5g, but it is not uncommon for the average intake in Japan to exceed twice that amount [ref:5].

Modern Humans Live in a World of Abundance

Modern humans no longer need to run for miles chasing prey. High-calorie food is available anytime at supermarkets and convenience stores. Yet our bodies remain programmed to "take in surplus calories and store them as fat." This evolutionary mismatch is considered one of the underlying factors behind the global obesity pandemic [ref:3].

In addition, the excessive salt intake of modern people can cause high blood pressure, which may seriously damage the heart and kidneys. High blood pressure is often called a "silent killer" because it progresses without symptoms while raising the risk of fatal conditions such as stroke and heart attack.

Also not to be overlooked is its impact on mental health. Humans once evolved a stress-response system to instantly decide "fight or flight" when encountering a predator. This system triggers a surge of stress hormones such as adrenaline and cortisol, putting the body on high alert. Today, we no longer worry about being attacked by wild animals on a daily basis, but this stress-response system still remains in our bodies. Work pressure, relationship troubles, and information overload from social media have become chronic stressors, and it has been suggested that this system—originally designed to handle short-term crises—continues to operate excessively, potentially leading to chronic anxiety disorders and depression [ref:6]. The instinct to submit to or hide from predators is thought to be internalized, and this may be a distant cause of modern-day stress and depression.

Modern Disease as the Price of Evolution—What Are We Genetically Predisposed To?

From all this, we can understand that major modern diseases such as obesity, heart disease, high blood pressure, and depression are conditions we are genetically predisposed to. These are not simply lifestyle issues; to a large extent, they stem from a mismatch between genetic programming shaped over hundreds of thousands of years and the modern environment.

• Obesity: the "thrifty gene," which efficiently stores energy as fat, backfires in an age of abundance
• High blood pressure and heart disease: a taste for salt combined with excessive sodium intake damages blood vessels and organs
• Depression and anxiety disorders: the predator-alert system becomes overactive in a chronically stressful society
• Type 2 diabetes: insulin resistance, once advantageous against famine, becomes a disease driver under a modern high-sugar diet

Solutions Brought by Advances in Genetic Medicine

For modern human DNA to undergo evolutionary changes adapted to today's living environment would require thousands of generations—that is, an enormous amount of time. There is an unbridgeable gap between the pace of natural selection and the speed of civilization's development. This is where Dr. Goldman focuses attention on advances in modern medicine, particularly the development of genetics and genomic medicine.

With today's technology, it has become possible to sequence the entire human genome (approximately 3 billion base pairs) relatively quickly. The Human Genome Project once took 13 years and about $3 billion, but with the advent of next-generation sequencers, we now live in an era where genome sequencing can be completed within a few days for a few hundred dollars [ref:7]. This revolutionary technology is opening up approaches such as the following.

1. Genetic disease screening: detecting gene mutations linked to specific disease risks early and taking preventive action
2. Personalized medicine (precision medicine): customizing treatment to an individual's specific genetic factors to achieve greater efficacy with fewer side effects
3. Genetic counseling and self-care: understanding one's own genetic traits to choose the best approach to diet, exercise, and stress management in daily life

By understanding genetics more deeply, we can become more accepting of our own bodies and practice self-care grounded in scientific evidence. Finding answers to questions like "Why do I gain weight easily?" or "Why am I so vulnerable to stress?" from the perspective of evolutionary history and genetics is a first step toward deeper self-understanding and designing a healthier life.

Conclusion—Understanding the Benefits and Costs of Evolution

The genetic traits humanity acquired over hundreds of thousands of years of evolution were essential for surviving the harsh conditions of prehistoric life. But in the dramatically changed environment of today, those same traits have become factors that raise the risk of diseases such as obesity, high blood pressure, heart disease, and depression. Understanding this "evolutionary mismatch" correctly is extremely important for improving our health management with the help of modern medicine and genetics. As genome analysis technology advances by leaps and bounds and an era of personalized medicine based on each individual's genetic background approaches, we are called upon to calmly reconsider both the benefits and the costs of evolution.

Frequently Asked Questions

Q1. What is the "thrifty gene"?

A. The thrifty gene is a group of genes that were advantageous for efficiently storing scarce energy as body fat during eras when food was often scarce. While advantageous for survival during times of famine, in today's era of food abundance it acts as a factor that raises the risk of obesity and type 2 diabetes [ref:4].

Q2. Why do humans tend to consume too much salt?

A. Early humans sweated heavily during long hunts, in an environment where sodium (salt) was easily lost, so their taste evolved to strongly favor salt. This preference has been genetically passed down to us today, and many people tend to consume more salt than they need. Excessive salt intake is a major risk factor for high blood pressure [ref:5].

Q3. What is the evolutionary mismatch hypothesis?

A. The evolutionary mismatch hypothesis is the idea that while human genetic traits are adapted to past environments, the rapid change in modern living conditions has caused those very adaptations to trigger health problems instead. Modern diseases such as obesity, heart disease, and depression are said to be explainable by this "mismatch" [ref:3].

Q4. Why does the stress response lead to depression?

A. Humans developed a "fight or flight" stress-response system to protect themselves from predators. This system was originally meant to handle short-term crises, but it can become constantly activated by the chronic stress environments of modern life (work, relationships, information overload, and so on). When stress hormones such as cortisol continue to be secreted at high levels over the long term, it can adversely affect brain function and potentially trigger depression and anxiety disorders [ref:6].

Q5. How will genome analysis help with future health management?

A. Advances in genome analysis technology are making "personalized medicine (precision medicine)" a reality—identifying an individual's genetic disease risk in advance and choosing preventive measures and treatments accordingly. For example, it has become clear that certain drugs are more effective for people with specific gene mutations, marking a shift from "one-size-fits-all treatment" to "treatment optimized for the individual" [ref:7].

[References]