A baby's brain development is shaped by both genetics and environment working together. Genes provide the blueprint, building the brain's basic structure and timing its growth, while a child's everyday experiences (talk, play, affection and new things to explore) decide which connections are strengthened. In the first few years, more than a million new neural connections form every second, which is why a rich, loving and stimulating environment matters so much.
Key takeaways
- Genes set the blueprint; experiences shape how it is built. It's nature and nurture, not one or the other.
- More than one million new neural connections form every second in the first few years of life.
- By around age five, a child's brain has reached about 90% of its adult size.
- Toddlers who hear more talk show stronger development in the brain's language pathways.
- Epigenetics explains how experience changes the way genes are expressed, without changing the DNA itself.
A baby's brain: a super-highway of connections
A baby's brain is naturally holistic: a super-highway network of around 86 billion brain cells and countless connections that create an ever-growing web of knowledge. Young children actually have far more neural connections than adults, which makes their brains like supercomputers running at full power. The secret to nurturing these little learning machines lies in two key strategies:
- Create a stimulating environment packed with engaging activities that ignite new brain connections and let them enjoy the joy of learning new things.
- Introduce new topics and ideas in a way that helps their brains organise and strengthen those neural networks, like building the most intricate brain map imaginable.
Their brains are performing mental gymnastics around the clock, and our role is to support them with the right environment. If you'd like to see what that looks like day to day, read how much young children can really learn.
How fast does a baby's brain grow?
During the first few years of life, a child's brain grows remarkably fast. In the early years it creates more than one million new neural connections (synapses) every second, more than at any other time in life (Zero to Three). By around age five, the brain has reached about 90% of its adult size (First Things First).
This rapid development is not driven by genetics alone. Environmental factors play a critical role in how these connections form and strengthen.
How does the environment shape brain development?
The environment a child grows up in strongly influences their cognitive development. Children who are surrounded by rich language, through talking, reading and singing, develop stronger connections in the areas of the brain that process language.
A study from Durham University found a direct link between the amount of speech toddlers hear and the structure of their brains: toddlers who heard more talk had higher levels of myelin, which supports fast, efficient brain signalling (Durham University). This is why everyday conversation matters so much. There are simple ideas in am I doing enough for my child's development?
Why play and new experiences matter
A stimulating environment involves much more than toys. Engaging, varied activities help babies develop problem-solving, motor skills and social skills. The experiences children have in this formative period build their unique brains.
The first 1,000 days of life are widely recognised as vital for laying the foundations of future learning, behaviour and health (Community Playthings). During this time the brain's capacity for change is at its peak, so the environments we create can either support or hold back learning.
Are babies' brains already "wired" at birth?
Partly. Researchers at King's College London found that newborn brains already show left-right asymmetries similar to adults', especially in areas used for language and vision, suggesting some features are hard-wired before birth (King's College London). Understanding these patterns helps scientists recognise typical and atypical development.
The importance of early experiences
The experiences infants meet shape their neural architecture profoundly. Affectionate interactions with caregivers help wire up connections within the brain (Welsh Government, Parenting. Give it time). As children engage with their surroundings, through play and through interaction with adults, their brains adapt and fine-tune themselves. That is why early experiences set the stage for lifelong learning.
How do toddlers' thinking skills develop?
As children move from infancy to toddlerhood, big changes happen in the brain. Researchers at the University of Bristol found that from around 16 months, toddlers start using more regions of their brains for important thinking skills such as following instructions and controlling impulses (University of Bristol). This is a key period for developing the "executive functions" that help children manage their thoughts and behaviour.
What role do genes play in brain development?
At conception, a child inherits around 20,000 genes from their parents, which form the blueprint for development. These genes guide many biological processes, including the formation of neurons and of the connections between them. For example, the ASPM gene is essential for producing new nerve cells in the developing brain, and changes in it can cause microcephaly, where the brain does not grow to its normal size (NINDS).
A large share of our genes is active in the developing brain, and which genes are switched on changes across the stages of life. During fetal development and early childhood, they orchestrate neuron migration, the formation of synapses and the brain's chemical signalling (review in PMC).
How do genetics and environment work together?
Genetics provides a roadmap, but environment decides how that potential is realised. The old "nature versus nurture" debate has given way to the understanding that the two are deeply intertwined. A child's genetic tendencies can even shape the responses they get from caregivers, which in turn shapes their development.
A study from the Université de Montréal found that genetic variants linked with higher birth weight are associated with greater growth of the cerebral cortex, but that this effect depends on the environment, such as the food available during pregnancy (Université de Montréal).
What is epigenetics?
Epigenetics describes how experiences can change the way genes are expressed without changing the DNA sequence itself. Experiences, both positive and negative, can therefore have lasting effects on brain development (Centre for Early Childhood).
The Harvard Center on the Developing Child compares the epigenome to the annotations on a musical score: the music (the genetic code) stays the same, but each performance (development) can vary greatly with its context. This helps explain why identical twins, with the same genes, can develop differently.
Critical periods of development
Some periods of brain development are especially sensitive. Different brain structures mature on their own timetables, and during these windows particular genes are more or less active, affecting how strongly children respond to their environment. In early childhood, genes involved in synaptic plasticity, which is essential for learning and memory, are highly active.
What does this mean for parents?
Genetics lays the groundwork for a child's potential, but it is the interplay between nature and nurture that shapes the outcome. Because the early years are when the brain is most adaptable, a warm, talkative, varied environment is one of the most powerful gifts you can give your child. That doesn't mean expensive toys; it means conversation, books, real experiences and new things to discover. Reading together is one of the best places to start: see how to help your child learn to read at home.
Frequently asked questions
Is intelligence determined by genes or environment?
Both. Genes influence a child's potential, but environment and experience strongly affect how that potential develops, especially in the early years when the brain is most adaptable.
What is the most important period for brain development?
The first few years of life, and especially the first 1,000 days, when the brain grows fastest and forms connections at a rate it will never reach again.
How can I support my baby's brain development?
Talk, read and sing to your baby every day, respond warmly to them, and offer varied, novel experiences, from new places and sounds to new textures and tastes.
Learn more
My book Tomorrow's Child Starts Today turns the science of the early years into practical, everyday ideas for parents. Read a free chapter extract to see if it's for you.
About the author
Teri Farrari is a developmental psychologist, natural health practitioner and early years consultant with more than thirty years' experience with young children and their families. She founded and ran her own Holistic Early Learning Schools, and her work has featured on BBC News, Sky Television, The Sunday Times, the Daily Mail and in Parents magazine. Read more about Teri or work with her one-to-one.
Nice blog
Nick ·