An example of the influence of nature is eye color, which is determined almost entirely by the genes you inherit from your parents. But nature’s reach extends far beyond simple physical traits. In the nature vs. nurture debate, “nature” refers to any trait, behavior, or ability shaped by your biological makeup, specifically your DNA. Understanding which characteristics fall on the nature side helps clarify how much of who you are was set in motion before you were born.
Physical Traits: The Clearest Examples
The most straightforward examples of nature’s influence are physical characteristics that follow predictable inheritance patterns. Eye color, blood type, earlobe attachment (free-hanging or attached), and even earwax type (wet or dry) are all determined by which versions of specific genes you receive from each parent. These are sometimes called Mendelian traits because they follow the basic dominant-and-recessive rules first described by Gregor Mendel. You can’t exercise your way to a different blood type or change your natural eye color through life experience. These traits are purely genetic.
Inherited diseases offer an even starker example. Huntington’s disease is caused by a single gene mutation on chromosome 4. If one parent carries that mutation, each child has a 50% chance of inheriting it. No amount of lifestyle change, parenting style, or environmental exposure alters that probability. The disease is entirely a product of nature.
Intelligence Has a Strong Genetic Component
Intelligence is more complex than eye color because environment clearly plays a role, but the genetic contribution is substantial and grows over time. A large study of 11,000 twin pairs across four countries found that the heritability of general cognitive ability rises linearly with age: about 41% in childhood (around age 9), 55% in adolescence (around age 12), and 66% by young adulthood (age 17). In other words, by the time you’re a teenager, roughly two-thirds of the variation in cognitive ability between people can be traced to genetic differences.
The landmark Minnesota Study of Twins Reared Apart drove this point home. Researchers tracked identical twins who had been separated at birth and raised in completely different families. About 70% of the variation in IQ scores was associated with genetic variation. These twins had different parents, different schools, different neighborhoods, yet their intelligence scores were remarkably similar. That similarity is nature at work.
Personality Is Partly Inherited
Your personality feels deeply personal, shaped by your experiences and choices. Yet twin studies consistently show that genetics account for a meaningful share of personality differences. Psychologists measure personality across five broad dimensions: neuroticism, extraversion, openness, agreeableness, and conscientiousness. A twin study estimated the genetic contribution to each at 41%, 53%, 61%, 41%, and 44%, respectively. Openness to new experiences, the most heritable of the five, is more than 60% attributable to genetic factors.
The Minnesota twin study reinforced this finding from a different angle. On multiple measures of personality, temperament, occupational interests, leisure-time interests, and social attitudes, identical twins raised apart were about as similar as identical twins raised together. Growing up in the same household added almost nothing to personality similarity beyond what shared DNA already explained.
The Biological Basis of Language
Every healthy human child learns to speak. No other species does. Rocks, rabbits, and toddlers can all be placed in an English-speaking community, but only the toddler will learn English. That observation, famously made by linguist Noam Chomsky, points to something hardwired in human biology that makes language acquisition possible. The idea, known as Universal Grammar, proposes that all human languages share deep structural similarities because they all emerge from the same innate biological blueprint. The specific language you speak is nurture. The capacity to speak any language at all is nature.
Your Sleep Preferences Are in Your Genes
Whether you’re naturally a morning person or a night owl is partly genetic. A specific gene called PER3 contains a repeating DNA segment that comes in two lengths. People who carry two copies of the longer version tend to wake earlier, go to bed earlier, and feel most alert in the morning. Those with two copies of the shorter version lean toward evening activity and later sleep times. Your work schedule and alarm clock can override these tendencies, but the underlying preference is biological. It’s one of the more surprising everyday examples of nature shaping daily life.
Mental Health: Nature Sets the Stage
Many mental health conditions have a clear genetic component, though they rarely come down to a single gene. Schizophrenia is a useful case study. Among identical twins (who share 100% of their DNA), if one twin develops schizophrenia, the other has a 33% chance of developing it too. For non-identical twins (who share about 50% of their DNA), that rate drops to 7%. The gap between 33% and 7% reflects genetic influence. But the fact that 33% is far from 100% shows that genes alone don’t seal the outcome. Conditions like bipolar disorder, autism, Alzheimer’s disease, and Parkinson’s disease follow a similar pattern: significant genetic risk shaped by environmental factors.
When Nature and Nurture Interact
Some of the most fascinating examples of nature’s influence only become visible when the environment activates a genetic predisposition. A well-studied example involves a gene that controls how the brain breaks down certain chemical messengers. People carry either a high-activity or low-activity version of this gene. The low-activity version, sometimes called the “warrior gene,” has been linked to higher rates of antisocial behavior, but only in individuals who also experienced childhood maltreatment. People with the same genetic variant who grew up in stable environments showed no elevated risk. The gene loaded the gun; the environment pulled the trigger.
This pattern of gene-environment interaction is now considered the most accurate way to think about nature’s influence on complex traits. Genes rarely operate as simple on-off switches for behavior. Instead, they shape how sensitive you are to your surroundings, how efficiently your brain processes stress, and how readily you develop certain skills. Nature provides the raw material. Environment sculpts it. But without the raw material, there would be nothing to sculpt.