Among great apes, we humans stick out—and our uber-impressive noggins deserve much of the credit. But sussing out the cognitive differences between the brains of people and other primates isn’t easy. To accomplish the task, researchers have done everything from mining the fossil record to shoring up the language learning skills of gorillas.
Now, an international team of researchers has entered the fray with an ambitious new technique: watching human, chimpanzee, and macaque brains grow from scratch in a dish.
Well, sort of. These lab-raised “brains” are technically organoids, three-dimensional clumps of cells that can self-organize and work together like a simple organ. Their findings, published today in the journal Nature, reaffirm that few structural differences exist between us and our cousins. But at the level of gene expression, the human organoids seemed to lag behind their great ape counterparts, taking longer to mature.
To grow the organoids, a team led by Gray Camp, a stem cell biologist at the Max Planck Institute for Evolutionary Anthropology in Germany, collected human, chimpanzee, and macaque cells and used a cocktail of chemicals to coax them into developing as neurons, or brain cells. Though done in a dish, the process is meant to mimic what happens in a developing embryo, with cells specializing and communicating with each other to become functional tissues.
The team’s method marks the first time researchers have been able to directly compare the developing organs of humans and great apes, Camp told Clare Wilson at New Scientist.
For four months, the researchers monitored the cells, occasionally sampling their genetic material to track how the organoids were progressing along the typical developmental trajectory. Though the mini-brains looked mostly the same by eye, their gene expression patterns told a different story. At the same point in time, the chimpanzee and macaque neurons seemed more mature, while their human counterparts lagged behind in a way that was “striking,” Camp told Laura Sanders at Science News.
It’s not totally clear why the delay exists or what effects it might have on cognitive ability. But the results do echo a pattern in human development: Even after we’re born, our brains continue to change and mature, settling down only after adolescence. Now, it seems it’s possible the process takes it sweet time from start to finish.
What’s observed in an organoid, however, won’t necessarily translate over to a full-blown brain, other researchers caution. The complexities of brain development in an actual fetus can’t be captured by a cluster of cells in a dish, Gül Dölen, a neuroscientist at Johns Hopkins University who was not involved in the study, told Ryan F. Mandelbaum at Gizmodo.
“It’s still early days in the organoid world,” Paola Arlotta, a neurobiologist at Harvard University who wasn’t involved in the study, told Sanders. But, she adds the results still highlight “important differences” in the development of humans and their closest relatives on the tree of life. That, at least, is worth some thought.