Scientists have inserted a human gene in the brains of monkeys to make them larger and more wrinkled in disconcerting lab experiments. .

Genetically tweaked marmoset brains were found to mimic the natural bumps and indentations in human brains, known as the gyri and sulci, respectively – an evolutionary trait in humans to increase surface area for neurons (nerve cells).  .

Image a brain hemisphere of a marmoset foetus grown with human gene ARHGAP11B.

'We found indeed that the neocortex of the common marmoset brain was enlarged and the brain surface folded,' said study author Michael Heide at the Max Planck Institute of Molecular Cell Biology and Genetics (MPI-CBG). 

The walnut-like appearance of the human brain, an evolutionary trait to increase its surface area for neurons (nerve cells), is made of what's called sulcus (the depression) and gyrus (the elevation)

Pictured in this illustration, a side view of the brain of the common marmoset, which lacks the walnut-like grooves of a human brain

'We confined our analyses to marmoset foetuses, because we anticipated that the expression of this human-specific gene would affect the neocortex development in the marmoset,' said study author Wieland Huttner at MPI-CBG.  

Researchers isolated different sub-populations of human brain stem cells and identified which genes are active in which cell type. 

Tests at the time on mouse embryos revealed that the gene can have a huge impact on brain development

Embryos injected with the gene grew larger brain regions and some developed the wrinkled surface that's characteristic of the human brain

'It is so cool that one tiny gene alone may suffice to affect the phenotype of the stem cells, which contributed the most to the expansion of the neocortex,' study lead author Marta Florio at MPI-CBG told LiveScience at the time.