The age-old question of “nature versus nurture” has fascinated scientists, philosophers, and curious minds for centuries. As we advance in our understanding of genetics and human development, we’re beginning to unravel which aspects of who we are come from our DNA and which are shaped by our experiences. Understanding this distinction isn’t just academic curiosity—it has profound implications for how we view ourselves, raise our children, and approach health and wellness.
This comprehensive guide explores the fascinating world of genetic determination, examining which human traits are primarily influenced by our inherited blueprint and how these genetic factors interact with environmental influences to create the unique individuals we become.
Understanding Genetic Influence: The Foundation of Human Traits
Your genes hold the basic instructions for your body to grow and function, but they are far from the only thing controlling your traits. Most traits are shaped both by a person’s genes and by environmental factors.
Many researchers consider the interaction between heredity and environment—nature with nurture as opposed to nature versus nurture—to be the most important influencing factor of all.
To understand which traits are primarily genetic, it’s essential to grasp the concept of heritability. The extent to which a characteristic – like height – can be explained by your genes, as opposed to the environment, is called heritability. For example, scientists have estimated that about 60 to 80 per cent of a person’s height is determined by their genes and 20 to 40 per cent is determined by their environment.
A trait or behavior that is wholly due to genetics has 100 percent heritability; one that is wholly due to the environment has zero heritability.
However, it’s important to understand that very few human traits fall at these extremes—most exist somewhere in between.
Physical Characteristics: The Most Genetically Determined Traits
Eye Color: A Complex Genetic Symphony
One of the most visible examples of genetic determination is eye color. Eye color is determined by variations in a person’s genes. Most of the genes associated with eye color are involved in the production, transport, or storage of a pigment called melanin. Eye color is directly related to the amount of melanin in the front layers of the iris. People with brown eyes have a large amount of melanin in the iris, while people with blue eyes have much less of this pigment.
To date, eight genes have been identified which impact eye color. The OCA2 gene, located on chromosome 15, appears to play a major role in controlling the brown/blue color spectrum. Today, scientists have discovered that at least eight genes influence the final color of eyes. The genes control the amount of melanin inside specialized cells of the iris. One gene, OCA2, controls nearly three-fourths of the blue-brown color spectrum.
Contrary to the simplified model many of us learned in school, researchers used to think that eye color was determined by a single gene and followed a simple inheritance pattern in which brown eyes were dominant to blue eyes. However, later studies showed that this model was too simplistic. The inheritance of eye color is more complex than originally suspected because multiple genes are involved.
Height: A Polygenic Powerhouse
Height represents one of the most studied examples of polygenic inheritance—traits controlled by multiple genes. Scientists estimate that about 80 percent of an individual’s height is determined by the DNA sequence variations they have inherited, but which genes these changes are in and what they do to affect height are only partially understood. For most individuals, though, height is controlled largely by a combination of genetic variants that each have more modest effects on height, plus a smaller contribution from environmental factors (such as nutrition). More than 700 such gene variants have been discovered and many more are expected to be identified.
Human height is controlled by many genes; in fact, there are over 400 genes related to height, and all of these genes interact to make up a person’s phenotype. This is a very large number, but it makes sense because height is a compilation of the lengths of many different body parts, such as leg bones, the torso, and even the neck. It is estimated that 90% of a person’s adult height is controlled by genetics, and 10% is affected by the environment.
Hair Texture and Other Physical Features
Round hair follicles make straight hair, flattened or c-shaped hair follicles make curly hair, and oval hair follicles make wavy hair. Curly hair is influenced by genes much more than by the environment. While curly hair runs in families—people with curly hair tend to have children with curly hair—its inheritance patterns are often unpredictable. Multiple genes control hair texture, and different variations in these genes are found in different populations.
A few biologically determined characteristics include genetic diseases, eye color, hair color, and skin color.
However, even these seemingly straightforward traits can be influenced by environmental factors in complex ways.
Temperament and Personality: The Genetic Foundation of Behavior
Understanding Temperament vs. Personality
Temperament includes behavioral traits such as sociability (outgoing or shy), emotionality (easy-going or quick to react), activity level (high or low energy), attention level (focused or easily distracted), and persistence (determined or easily discouraged). These examples represent a spectrum of common characteristics, each of which may be advantageous in certain circumstances. Temperament remains fairly consistent, particularly throughout adulthood.
Your temperament affects how you behave and how you interact with your environment. Your personality, on the other hand, encompasses your beliefs, thoughts, traits, characteristics, and behaviors that develop as you age. Your temperament includes the basic dispositional traits that you are largely born with. It is temperament that influences how you behave, your social interactions, and how you respond to the environment. Such experiences then play a part in shaping the development of your personality.
The Heritability of Temperament
Research consistently demonstrates strong genetic influences on temperament. Scientists estimate that 20 to 60 percent of temperament is determined by genetics. Temperament, however, does not have a clear pattern of inheritance and there are not specific genes that confer specific temperamental traits. Instead, many (perhaps thousands) of common gene variations (polymorphisms) combine to influence individual characteristics of temperament.
In their research on twins, scientists have found that personality is roughly between 30% and 60% heritable.
Twin studies provide compelling evidence for genetic influence: Studies of identical twins (who share 100 percent of their DNA) and their non-twin siblings (who share about 50 percent of their DNA) show that genetics play a large role. Identical twins typically have very similar temperaments when compared with their other siblings. Even identical twins who were raised apart from one another in separate households share such traits.
The Big Five Personality Traits
The Big Five personality model—consisting of openness, conscientiousness, extraversion, agreeableness, and neuroticism—has provided a framework for understanding genetic influences on personality. Research indicates that heritability explains around 40% to 60% of the variance in the Big Five personality traits. Each of these five traits represents a continuum.
Temperament, a key aspect of personality, is highly influenced by genetics. Certain traits such as extroversion, introversion, neuroticism, and conscientiousness have been found to have a strong heritable component.
Specific Genetic Influences on Behavior
Recent advances in molecular genetics have begun to identify specific genes that influence temperament and personality. Variants affecting the PCDH15 and WSCD2 genes are associated with sociability, while some MAOA gene variants may be linked to introversion, particularly in certain environments. Variants in several genes, such as SLC6A4, AGBL2, BAIAP2, CELF4, L3MBTL2, LINGO2, XKR6, ZC3H7B, OLFM4, MEF2C, and TMEM161B contribute to anxiousness or depression.
Recent genome-wide association studies (GWAS) have shown that temperament is strongly influenced by more than 700 genes that modulate associative conditioning by molecular processes for synaptic plasticity and long-term learning and memory. The results were replicated in three independent samples despite variable cultures and environments.
Intelligence and Cognitive Abilities: A Complex Genetic Landscape
The Genetic Component of Intelligence
Intelligence represents one of the most studied yet complex examples of genetic influence on human traits. Like most aspects of human behavior and cognition, intelligence is a complex trait that is influenced by both genetic and environmental factors. Intelligence is challenging to study, in part because it can be defined and measured in different ways. Most definitions of intelligence include the ability to learn from experiences and adapt to changing environments. Elements of intelligence include the ability to reason, plan, solve problems, think abstractly, and understand complex ideas.
Studies have shown that intelligence has a genetic component, but they have not conclusively identified any single genes that have major roles in differences in intelligence. It is likely that intelligence involves many genes that each make only a small contribution to a person’s intelligence.
Environmental Interactions with Genetic Potential
Intelligence is also strongly influenced by the environment. During a child’s development, factors that contribute to intelligence include their home environment and parenting, education and availability of learning resources, and healthcare and nutrition.
A person’s environment and genes influence each other, and it can be challenging to tease apart the effects of the environment from those of genetics. For example, if a person’s level of intelligence is similar to that of their parents, is that similarity due to genetic factors passed down from parent to child, to shared environmental factors, or (most likely) to a combination of both? It is clear that both environmental and genetic factors play a part in determining intelligence.
Genetic vs. Environmental Interactions: The Complete Picture
How Genes and Environment Work Together
Understanding genetic determination isn’t simply about identifying which traits are “genetic” versus “environmental.” Environmental factors often influence traits independently of genes. But not always. Sometimes the environment changes a gene—either its DNA sequence or its activity level. Either of these effects can change the proteins that are made from a gene, which in turn affects traits.
Instead, these influences include genetic factors, environmental factors, and how each intermingles with the other. While the nature and nurture debate is often presented in a way suggesting traits are caused by either genetics or environment, it’s important to remember that it’s much more complex than that. Today, experts recognize that not only do both nature and nurture play a role, it is often the unique interaction of the two that is responsible for how certain characteristics or behaviors are expressed.
Environmental Influence on Gene Expression
Environmental factors also play a role in temperament by influencing gene activity. In children raised in an adverse environment (such as one of child abuse and violence), genes that increase the risk of impulsive temperamental characteristics may be turned on (activated).
For instance, children raised in adverse conditions, such as with neglect, abuse, or poverty, are typically found to be more impulsive. Scientists say this is because this environment “activates” impulsive temperament genes that may have otherwise been dormant. Meanwhile, those raised in healthy, nurturing, safe environments are more likely to have calmer temperaments because different genes are then activated.
Traits with Lower Genetic Determination
Learned Behaviors and Skills
Some traits are controlled by genes that pass from parent to child. Others are acquired through learning. But most are influenced by a combination of genes and environmental factors.
Many complex human behaviors, skills, and preferences show lower heritability than physical traits or basic temperament.
Language acquisition, specific academic skills, cultural practices, and social behaviors are examples of traits where environmental factors typically play a larger role than genetics, though genetic factors still contribute to individual differences in aptitude and ease of learning.
The Role of Culture and Society
They argue that our understanding of the environment is flawed. “Since its founding, the field of behavioural genetics has quantified the influence of genes by contrasting it with influence from the environment, but it has relied on an impoverished conception of the environment,” explains researcher Dr Uchiyama. “When you take into account how culture and cultural evolution shape the environment, then you see the idea of heritability in a very different light and realise the old nature/nurture dynamic is much more complicated than was previously thought to be the case,” explains Dr Uchiyama. He continues: “You can’t so easily say that genes explain X per cent of a trait and the environment explains the other Y per cent because culture may have levelled out the playing field and reduced variation in the environment, making the environment similar for most people in a society or a group within a society.
Modern Genetic Research: New Discoveries and Future Directions
Advances in Molecular Genetics
One of the most exciting new directions for research on personality and temperament comes from recent advances in molecular genetic techniques that now make it possible to identify genes associated with complex phenotypes. Complex behavioral traits are unlikely to result from the action of major genes segregating in a simple Mendelian fashion, but are expected to result from the action or co-action of a few (oligo) or many (poly) genes.
Researchers also specifically discovered 42 sets of genetic variations (associated with 727 specific areas in our DNA) that appear to be strongly linked to personality traits.
The Missing Heritability Problem
Despite advances in genetic research, scientists still face the “missing heritability” problem. As described here, there are several reasons why genome-wide association studies are currently under-detecting the DNA variations that contribute to the heritability of characteristics. Much higher estimates of heritability come from studies that consider all the genome’s SNPs simultaneously to determine to what extent people with more similar genomes are more similar in a particular characteristic. This suggests that future, more powerful genome-wide association studies to identify influential genes will partly reduce the “missing heritability” gap.
Practical Implications: What This Means for Daily Life
Understanding Individual Differences
Recognizing which traits are primarily genetic can help us better understand individual differences and set realistic expectations. In the end, it’s a mix of things we can and can’t control that determines our traits. As one example, we can’t control the risk for heart disease that comes from genes, nor environmental factors like age and gender. But these factors don’t determine our destiny. Our behaviors play a large part as well: the foods we eat, physical activities we pursue, and decisions about smoking all shape our risk of getting sick.
Parenting and Education
Understanding genetic influences on traits like temperament and intelligence can inform parenting and educational approaches. Rather than trying to change fundamental aspects of a child’s temperament, parents and educators can work with these genetic predispositions to help children develop their strengths and manage their challenges.
Medical and Therapeutic Applications
Instead, most diseases are complex and stem from an interaction between your genes and your environment. As scientists learn more about the connection between genes and the environment, they pursue new approaches for preventing and treating disease that consider individual genetic codes.
Limitations and Misconceptions
Common Misunderstandings
It’s crucial to avoid genetic determinism—the belief that genes entirely control human traits and destiny. According to current research, personality traits appear to come from a combination of genetic (30% to 60%) and environmental factors. In some cases, environmental factors (such as abuse) may “switch on” certain genes that were dormant before, such as impulsivity.
The Complexity of Genetic Expression
Apart from blood type (AB, A, B or O), virtually all characteristics that vary between humans are complex traits, influenced by many genes (and that includes many characteristics commonly, but wrongly, thought to be determined by a single gene such as eye colour, tongue rolling and chin clefts!).
Conclusion: Embracing the Genetic-Environmental Dance
Understanding which traits are primarily determined by genetics provides valuable insight into human nature and individual differences. While physical characteristics like eye color and height show strong genetic determination, behavioral traits like temperament and personality represent complex interactions between multiple genes and environmental influences.
The research consistently shows that personality traits are moderately heritable, and can predict various lifetime outcomes, including psychopathology. However, this genetic influence doesn’t mean these traits are unchangeable—rather, it provides a foundation upon which environmental experiences build throughout life.
As we continue to advance in genetic research and understanding, it becomes increasingly clear that the old “nature versus nurture” debate is overly simplistic. Instead, we must appreciate the intricate dance between our genetic blueprint and our environmental experiences in shaping who we are.
Studies have concluded that human personalities and temperaments are shaped by both genetics and our environment; while we may be born with certain personality traits, there still is the possibility to develop others as we experience life.
By understanding which traits are primarily genetic, we can better appreciate our inherent strengths and challenges, make more informed decisions about our health and development, and ultimately work with—rather than against—our genetic predispositions to lead fulfilling, authentic lives. This knowledge empowers us to focus our energy on aspects of ourselves we can influence while accepting and embracing the unique genetic gifts that make us who we are.
