Not by Genes Alone

Introduction: How Culture Shapes Human Biology

The American South has historically exhibited higher rates of violence than the North, a pattern that persists in modern homicide statistics. While some might attribute this to climate or economics, research suggests the cause is a culturally acquired culture of honor. In this system, men believe their reputation is worth defending even at great physical or social cost. In laboratory settings, Southerners respond to insults with significant physiological spikes in stress and aggression hormones, whereas Northerners remain largely unaffected. This behavior is rooted in the history of the South, which was settled by livestock herders who lived in sparsely populated areas where livestock was easy to steal.

Culture is not a superorganic phenomenon existing entirely outside of human biology. It consists of practical information, including ideas, values, and skills, that people acquire from others through teaching and imitation. This vast amount of information is stored in human brains that have been shaped by millions of years of natural selection to learn and manage social behavior. Because culture is a fundamental part of our biological makeup, it can trigger physical responses, such as the hormonal shifts seen in the Southern culture of honor. To understand humans, scientists must track how cultural ideas spread or disappear based on how easy they are to learn, how attractive they are, or the social prestige of those who hold them.

A common mistake in science is to view human behavior as a strict choice between genetic nature and environmental nurture. In reality, every human behavior results from the continuous interaction between genetic information and the surrounding environment. Natural selection does not just create fixed, robotic behaviors; it shapes the way an organism flexibly responds to its surroundings. Culture adds a unique and powerful layer to this biological interaction. For example, while humans have an innate genetic aversion to bitter tastes to avoid natural toxins, we can culturally learn that a specific bitter plant has medicinal value or makes a stimulating beverage.

The human brain did not evolve to be a finished product that only later discovered culture as an afterthought. Instead, there was a constant evolutionary feedback loop between our developing psychology and the cultural information it was designed to process. During the rapid climate fluctuations of the last million years, the ability to imitate became a vital survival strategy for our ancestors. In highly unpredictable environments, relying on the collective wisdom of a group is often safer and more efficient than individual trial and error. This reliance on social learning led to a unique psychology that favors conformity and the imitation of successful individuals.

Because culture is subject to its own selective pressures, it acts as an ultimate cause of behavior, functioning much like genes do in biological evolution. Ideas that promote the survival and expansion of a group tend to persist and spread across generations. Over time, these cultural environments actually change the physical direction of genetic evolution. For instance, as early cultural institutions began to favor cooperation among larger groups, individuals who were genetically predisposed to be too aggressive or uncooperative were heavily disadvantaged. In this way, genes and culture coevolve, with each shaping the other in a process that has made humans the dominant species on Earth.