Why does the human brain take so long to develop? Scientists find a gene that may provide a clue about our extraordinary brainpower, cognitive abilities

What makes the human brain so unusually complex may have something to do with a surprisingly slow biological process.

Scientists at Columbia University's Zuckerman Institute have identified evidence that a human-specific gene influences the development of microglia — immune cells in the brain that play a crucial role in shaping neural connections. Unlike comparable cells in mice, human microglia can take four to eight years to reach maturity, according to findings reported by ScienceDaily.

The research suggests that the same evolutionary mechanism that slows the development of human neurons may also regulate microglia, potentially helping the two cell types develop in coordination.


The study was published in Neuron on August 31, 2026.

The surprising role of a human-only gene

The researchers focused on SRGAP2, a gene that has undergone human-specific duplication during evolution.

The Polleux laboratory at the Zuckerman Institute has spent more than 15 years investigating SRGAP2 and its role in distinguishing the human brain from those of other mammals.

Earlier research had shown that human-specific versions of the gene influence neurons by increasing the number of synapses they form while delaying the maturation of those connections.

That combination is thought to contribute to the dense networks found in the human brain.

But the latest research revealed something the scientists did not expect.

Human-specific copies of SRGAP2 were found at levels nearly 10 times higher in microglia than in neurons, ScienceDaily reported.

That observation prompted researchers to investigate why a gene already associated with human brain development was so active in these immune cells.

Microglia are more than the brain's immune system

Microglia have traditionally been viewed primarily as the brain's defense system.

They help identify and remove harmful material, clear damaged cells and respond to injury or infection.

Over the past two decades, however, scientists have learned that their role is considerably broader.

During brain development, microglia help determine which connections between neurons remain and which are removed. They can also influence how strongly synapses respond to signals.

In other words, these cells help sculpt the neural networks that allow the brain to function.

That makes their unusually slow development particularly interesting when researchers are trying to understand what makes the human brain different.

Humans take years while mice take weeks

One of the most striking findings concerns the pace at which microglia mature.

Researchers found that human microglia can require approximately four to eight years to reach maturity.

In mice, comparable cells mature in roughly three weeks.

The enormous difference fits into a broader biological pattern. Human brain development stretches across a much longer period than it does in many other mammals.

Scientists call this extended developmental timetable neoteny.

The idea is that keeping certain developmental processes active for longer could allow the human brain to build increasingly sophisticated circuits and connections.

The gene may synchronize different parts of brain development

The new research points toward SRGAP2 as a possible coordinator of that unusually prolonged development.

The researchers found that human-specific copies of the gene dramatically slowed the maturation of human microglia in experiments involving mouse models and human cells, according to ScienceDaily.

That mirrors the gene's previously identified effects on neurons.

The emerging picture is that SRGAP2 may help maintain a slower developmental rhythm across different types of brain cells.

Carlos Diaz-Salazar, the study's lead author, suggested that evolution may have selected the gene to regulate microglial development alongside neuronal development, keeping the two processes synchronized.

That could be important because neurons and microglia constantly interact while the brain is developing.

Could slow brain development be part of what makes us human?

The findings do not prove that SRGAP2 directly causes human intelligence or cognitive ability.

Instead, they offer a possible biological explanation for one feature that distinguishes human brain development from that of other animals: its extraordinary length and complexity.

A brain that develops slowly has more time for cells to interact, connections to form and circuits to be refined.

Researchers believe that this extended developmental window may have contributed to the emergence of sophisticated human cognitive abilities.

The new study adds microglia to that evolutionary picture.

The discovery could also shed light on brain disorders

The implications may extend beyond understanding human evolution.

Microglia have increasingly been linked to neurodevelopmental disorders as well as neurodegenerative diseases. Understanding why human microglia develop differently could therefore help scientists investigate how these cells behave when something goes wrong.

The Columbia researchers now want to determine precisely how SRGAP2 regulates the extended developmental process and whether similar mechanisms operate elsewhere in the brain.

The goal is not simply to identify another gene that differs between humans and other animals.

It is to understand how numerous biological changes work together to produce the human brain.

A new clue in the mystery of the human brain

The human brain contains an extraordinary network of neurons and connections, but those networks do not appear fully formed. They emerge through a prolonged period of development in which different cells constantly interact and reshape neural circuits.

The discovery surrounding SRGAP2 suggests that microglia may be following part of the same unusually slow timetable as neurons.

That could provide scientists with another piece of the evolutionary puzzle — one in which the remarkable capabilities of the human brain may be linked not only to how its cells develop, but also to how long they take to do it.

The study, “Human-specific SRGAP2 paralogs synchronize neotenic microglial maturation and synaptic development,” was published in Neuron by Carlos Diaz-Salazar, JaeYeon Kim, Marine Krzisch and colleagues.