Common marmosets have nearly smooth brains, unlike most primates, and a team at the German Primate Center in Göttingen now reports a cellular reason. Certain neural progenitor cells in marmosets divide significantly more slowly than the same cells in humans, and the marmoset window of rapid cell multiplication is shorter. The result is fewer neurons and a smaller, less folded cortex.
Help yourself and the planet: The Cool Down makes it easy to help yourself while helping the planet, with smart, simple changes to save more and waste less in your everyday life.
We may earn a commission if you sign up.
The study, led by PhD students Lidiia Tynianskaia and César Mateo Bastidas Betancourt, appears in volume 12, issue 39, of Science Advances. ScienceDaily dated its release Oct. 22, while the German Primate Center’s announcement circulated on Sept. 23.
Progenitor cells that divide slowly
The paper, titled Coordinated neural progenitor adaptations contribute to primate neocortical downscaling, looks at progenitors, the cells that generate the cortex’s neurons. According to the ScienceDaily release, two differences stood out. Some marmoset progenitors divide more slowly than their human counterparts, and others have simpler structures with fewer processes and are less proliferative. Bastidas Betancourt said certain progenitor cells in the common marmoset divide significantly more slowly than in humans.
Tynianskaia framed the question plainly: the team wanted to understand which changes at the cellular level cause the marmoset brain to grow less and form fewer folds. Common marmosets, Callithrix jacchus, are small New World monkeys, and the contrast with the heavily folded human cortex made them a useful comparison. The answer is not a single switch. No single change accounts for the effect, which fits the paper’s own wording about coordinated adaptations across several kinds of cells, and the release says the differences together reduce neuron output. A News-Medical summary of the German Primate Center release adds that marmoset brains start out with a typical large, folded primate structure, so whatever slows neuron production must act later in development.
The shorter window matters because the cortex is built from progenitors. Each round of division adds to the pool that eventually becomes neurons, so cells that divide slowly, or that stop rapid proliferation early, leave fewer neurons behind. The News-Medical summary says the timing of progenitor traits differs between species, which gives marmoset progenitors less time in the fast-dividing state than the human cells have.
Organoids as a stand-in for fetal tissue
Most experiments used brain organoids, small three-dimensional models grown from marmoset and human stem cells. Senior author Michael Heide, who heads the Junior Research Group Brain Development and Evolution and is described on his University of Göttingen faculty page as an ERC starting grant holder since 2022, said organoids suit the question because such sample sizes are not feasible in primates. He also said the study combines the advantages of in vivo and in vitro methods.
The team matched developmental stages across species before comparing them. A 50-day marmoset organoid corresponds closely to a natural marmoset brain at day 90, which allowed stage-by-stage comparison with human organoids. Key results were then repeated in fetal marmoset brain tissue to confirm that the organoids were not misleading. The abstract also draws on previously published histological data. Tynianskaia and Bastidas Betancourt share first authorship with a long author list that includes Esther Marie Grewe, Julia Marie Kniep, Neringa Liutikaite, Nesil Esiyok, İrfan Burak Göloğlu, Sabrina Heide, Nancy Rüger, Dimitri Lindenwald, Charis Drummer, Stoyan Petkov and Nataliya Di Donato.
A clue to wrinkles, with limits
Why brains fold is a long-standing question, and the finding suggests that modest changes in progenitor behavior and developmental timing can produce large differences in brain size and folding across primates. That is the sense in which the marmoset is a clue to human wrinkles: the human cortex may be the product of the same dials turned the other way, with progenitors that keep dividing for longer.
The causal story is hedged by the authors. A Neuroscience News report quotes the abstract as saying the adaptations likely constrain neuronal output, so the link to a smaller, less folded cortex is inferred rather than directly proven. Organoids are a model system, only some experiments were checked in fetal tissue, and the comparison covers two species.
The researchers say that understanding the cellular controls of folding may help explain human conditions in which normal folding fails to begin, such as lissencephaly, which means smooth brain, and microcephaly, and may help in studying developmental disorders. Researchers who study brain evolution often lean on such cross-species comparisons, since folding cannot be tested directly in living human embryos. Because marmosets are one of several primate species the Heide group plans to compare in organoids, alongside human, chimpanzee and rhesus macaque, the marmoset result reads as an opening comparison and not a final answer. No clinical findings in people are reported. For now the study is a map of how one small primate ends up with a smooth brain, built from comparisons of cells grown in the laboratory and a smaller number of confirmations in fetal marmoset tissue.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
Help yourself and the planet: Get The Cool Down →
We may earn a commission if you sign up.
More from Morning Overview
- Seven of Earth’s nine planetary boundaries are breached, and all seven are worsening
- The NSA says three phone features should be off whenever you aren’t using them
- Hurricane Hunter radar shows four warning signs that a tropical cyclone is about to strengthen, a University of Miami study found
- Tropical Storm Rachel is dumping up to 12 inches on four Mexican states on its way to major hurricane strength
