Scientists Double Size Of Monkeys’ Brains Using Human Genes

by : Emily Brown on :
Scientists Double Size Of Monkey's Brain Using Human GenesPixabay/20th Century Fox

Scientists managed to double the size of monkeys’ brains by injecting fetuses with human genes.

The study was carried out by researchers at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG) in Dresden, Germany, with colleagues at Japan’s Central Institute for Experimental Animals (CIEA) in Kawasaki and the Keio University in Tokyo.


In the experiment, the researchers injected the dark matter of marmoset fetuses with a gene called ARHGAP11B, which directs stem cells in the human brain.


The gene has been used in the past on mice and ferrets, with results showing that it causes an expanded neocortex in the animals, but its relevance for primate evolution was unclear until now.

A release about the study published by EurekAlert explains that the expansion of the human brain during evolution – specifically the neocortex – is linked to our cognitive abilities such as reasoning and language.


After injecting monkey brains with the gene, the scientists found they developed larger, more advanced neocortexes, making them more similar to the human brain.

Human brain diagramVisanji, Naomi P. et al./Wikimedia

The findings, published in the journal Science, showed that the modified brains had nearly doubled in size approximately 100 days into gestation.

The human neocortex is roughly three times bigger than that of the chimpanzee, our closest relative. During evolution the neocortex folded increasingly into wrinkles in order to fit inside the restricted space of the skull.


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Scientists have questioned how the human neocortex became so big, and the results of this study suggest the ARHGAP11B gene may be responsible for the expansion.

Study author Michael Heide commented:

We found indeed that the neocortex of the common marmoset brain was enlarged and the brain surface folded. Its cortical plate was also thicker than normal.

Furthermore, we could see increased numbers of basal radial glia progenitors in the outer subventricular zone and increased numbers of upper-layer neurons, the neuron type that increases in primate evolution.


Wieland Huttner, who led the study, explained that researchers confined their analysis to marmoset fetuses because they anticipated the gene to affect the neocortex development.

They continued:

In light of potential unforeseeable consequences with regard to postnatal brain function, we considered it a prerequisite – and mandatory from an ethical point of view – to first determine the effects of ARHGAP11B on the development of fetal marmoset neocortex.

After witnessing the results, the researchers involved in the project decided to abort the monkey fetuses due to the aforementioned ‘unforeseeable consequences’. The study has been likened to the 2011 film Rise of the Planet of the Apes, in which a race of genetically modified primates take over the Earth.


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Emily Brown

Emily Brown first began delivering important news stories aged just 13, when she launched her career with a paper round. She graduated with a BA Hons in English Language in the Media from Lancaster University, and went on to become a freelance writer and blogger. Emily contributed to The Sunday Times Travel Magazine and Student Problems before becoming a journalist at UNILAD, where she works on breaking news as well as longer form features.

Topics: Animals, Evolution, experiment, monkey, Now, Science


  1. EurekAlert

    Human brain size gene triggers bigger brain in monkeys