In child development, “nature” refers to the genetic and biological factors a child is born with that shape how they grow, think, and behave. It includes everything encoded in DNA: physical traits like eye color and height, but also less visible characteristics like temperament, cognitive ability, and vulnerability to certain conditions. Nature is one half of the classic “nature vs. nurture” framework, where nurture represents the environmental influences (parenting, nutrition, culture, experiences) that also shape development. Today, most researchers view the two not as competing forces but as deeply intertwined systems that constantly influence each other.
What “Nature” Actually Includes
When developmental scientists talk about nature, they mean the full biological blueprint a child inherits from both parents. This goes well beyond physical appearance. It includes the pace at which the brain matures, the sequence of motor milestones, hormonal patterns, and predispositions toward certain personality traits or learning styles. Some of these genetic instructions are fixed, like blood type. Others are more like tendencies, setting a range of possible outcomes that the environment then narrows or expands.
A clear example of nature at work is the universal sequence of physical development in infancy. Babies develop from the head downward: they gain head control before they can sit, sit before they crawl, and crawl before they walk. Between three and four months, neck muscles strengthen enough to hold the head steady with support. By five to six months, most infants can sit briefly on their own and begin rolling from back to stomach. Crawling typically emerges between six and nine months, and first independent steps appear around nine to twelve months. This sequence is remarkably consistent across cultures because it is driven by biological maturation, not teaching.
Temperament: The Genetic Starting Point
One of the most studied “nature” influences is temperament, the behavioral style a child shows from very early in life. Some babies are naturally more active, some more cautious, some quicker to laugh, some quicker to cry. Twin studies consistently show that identical twins are more similar in temperament than fraternal twins across a wide range of traits, including emotionality, activity level, shyness, sociability, attention span, and tendency toward positive or negative moods. Heritability estimates for these traits generally fall between 20% and 60%, meaning genetics accounts for roughly one fifth to three fifths of the variation seen across children.
What’s particularly interesting is that genetic influence on temperament isn’t static. Research from the Louisville Twin Study found that changes in temperament during infancy and early childhood are themselves partly regulated by genes. For traits like activity level, extraversion, and behavioral inhibition, the stability a child shows from one age to the next is almost entirely due to genetic factors. New genetic effects also appear to “switch on” at different ages, meaning nature doesn’t simply set a trait at birth and leave it alone. It continues to shape development as the child grows.
One specific genetic link researchers have identified involves a dopamine receptor gene (DRD4) associated with ADHD, which accounts for a small but measurable portion of genetic variance in activity level. This suggests that what we call hyperactivity in clinical settings may sit at the far end of a normal, genetically influenced spectrum of how active children naturally are.
How Genetics Shape Cognitive Ability
General cognitive ability, sometimes loosely measured as IQ, is one of the most heritable psychological traits, and its heritability changes with age in a way many people find surprising. A study of over 11,000 twin pairs from four countries found that genetic influence on cognitive ability increases linearly from childhood through young adulthood. At age nine, genetics accounted for about 41% of the variation in general cognitive ability. By age twelve, that rose to 55%. By seventeen, it reached 66%.
At the same time, the influence of shared environment (the home, neighborhood, and family resources children grow up with) moved in the opposite direction: from 33% at age nine, down to 18% at twelve, and 16% at seventeen. This doesn’t mean the environment stops mattering. Rather, as children gain more independence and begin choosing their own activities, friends, and interests, their genetic tendencies increasingly steer those choices, which in turn reinforce the traits they were already predisposed toward.
Why Nature Never Acts Alone
The modern understanding of nature in child development centers on gene-environment interaction, the idea that genes and surroundings are not separate inputs but a single feedback loop. One of the clearest illustrations comes from epigenetics, the study of how environmental conditions change the way genes are expressed without altering the DNA sequence itself.
During embryonic development, the chemical process that controls which genes are active and which are silent is especially sensitive to outside influences. Prenatal exposure to famine, for example, can leave lasting marks on gene expression. Researchers studying the Dutch Hunger Winter of 1944-1945 found that individuals who were exposed to famine in the womb had measurable differences in the expression of a growth-related gene (IGF2) compared with their unexposed siblings, and these differences were still detectable six decades later. Similarly, adult children of Holocaust survivors show altered expression of a gene involved in stress-hormone sensitivity, a change linked to their parents’ traumatic experiences rather than to their own.
These findings reveal that “nature” is not a fixed blueprint sealed at conception. Environmental exposures, particularly during pregnancy and early life, can chemically modify how genes behave, and some of those modifications persist for a lifetime or even pass to subsequent generations.
Three Ways Genes and Environment Overlap
Researchers describe three patterns through which a child’s genetic makeup becomes entangled with their environment, a concept called gene-environment correlation.
- Passive correlation happens because parents provide both genes and the home environment. A child born to musically talented parents inherits genetic predispositions toward musicality and grows up in a house full of instruments and music. The child didn’t choose either one.
- Evocative correlation occurs when a child’s genetically influenced traits draw specific responses from other people. A naturally cheerful, sociable toddler tends to receive more social interaction from caregivers and peers, which further develops their social skills.
- Active correlation emerges as children grow older and start selecting environments that match their genetic tendencies. An athletically inclined child gravitates toward sports teams; a curious, book-loving child seeks out libraries and reading groups.
Active correlation becomes more dominant with age, which helps explain why genetic influence on traits like cognitive ability increases as children move from childhood into adolescence. The older a child gets, the more freedom they have to shape their own environment in ways that reinforce their inborn tendencies.
Brain Maturation: A Built-In Timeline
The brain’s physical development follows a genetically driven schedule that unfolds over more than two decades. In prenatal life and early infancy, the brain rapidly produces neurons and forms connections between them. A second surge of this connection-building occurs just before puberty, followed by a long period of pruning and refinement that continues until roughly age 24.
Pruning eliminates unused connections, making the remaining neural circuits faster and more efficient. At the same time, the brain coats active nerve fibers in a fatty insulation layer that speeds up signal transmission. This process is especially prolonged in the prefrontal cortex, the region responsible for impulse control, planning, judgment, and decision-making. The fact that this area matures last is a direct product of biological programming and explains why adolescents often struggle with impulsive behavior even when they intellectually understand the risks.
While this timeline is genetically set, the connections that survive pruning depend heavily on experience. The brain preferentially keeps pathways that get used and discards those that don’t. So the biological schedule creates windows of opportunity, but what a child actually experiences during those windows determines the final wiring. Nature builds the scaffold; the environment fills it in.