The size of an animal’s brain is often attributed to the overall intelligence of the species. Of the primate species, humans tend to have larger brains (by ratio) and this is often presented as a reason for the species’ advanced intelligence. But if most of the primates shared an ancestor or evolved around the same time, why did the human brain evolve to be much larger than a gorilla or a chimpanzee? Also, can the ape-brain be manipulated to be more like a human’s? The answer is hidden in brain molecular biology.
Researchers at the Medical Research Council (MRC) Laboratory of Molecular Biology in Cambridge, UK, have identified a kind of molecular key or switch that can make ape brain organoids grow more like human organoids, and vice versa.
This study was conducted on lab-grown organoids; and not actual brains from the various species.
The researchers developed ‘brain organoids’ which are 3-Dimensional tissues grown from human, gorilla and chimpanzee stem cells. These organoids model early brain development. Much like humans in real life, these lab grown human organoid brains grew a lot larger than the organoids from other apes.
“This provides some of the first insight into what is different about the developing human brain that sets us apart from our closest living relatives, the other great apes,” said lead author Dr Madeline Lancaster from MRC. Their paper has been published in the journal Cell.
She further explained the most striking difference between all the brains was the large size of human brains.
Cylindrical shaped stem cell called neural progenitors form the brain neuron during the early stages of development by splitting into identical daughter cells. Gradually they develop a cone shape.
The study observed this transition process in gorillas and chimpanzees took up to five days. Whereas in humans, it was seven days. They maintained the cylinder shape longer, and split into more daughter cells during this time.
“It's remarkable that a relatively simple evolutionary change in cell shape could have major consequences in brain evolution,” Lancaster was quoted by Science Daily.
A gene called 'ZEB2' is responsible for this transition. When manipulated, it influenced the gorilla brain organoids to grow in a similar manner to human brain organoids.