Marmosets show interlinked qualities that indicate self domestication over time.
Even humans aren't done evolving, and marmosets have things in common with us.
The secret is in the multipurpose neural crest cells.
Are monkeys domesticating themselves over time? Scientists say that while “domestication syndrome” has been theorized since the days of Charles Darwin, a new study is the first concrete data to show a link between group behaviors and physical signs of individual domestication.
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In the new paper, Princeton University researchers study the combination of a specific facial fur patch on marmosets with a vocal pattern they say corresponds to the patch. It sounds wild:
“Here, we provide evidence that, in marmoset monkeys, the size of a domestication phenotype—a white facial fur patch—is linked to their degree of affiliative vocal responding. During development, the amount of parental vocal feedback experienced influences the rate of growth of this facial white patch, and this suggests a mechanistic link between the two phenotypes, possibly via neural crest cells.”
Neural crest cells are a population of “pluripotent cells that migrate to various parts of the body during development and whose derivatives include melanocytes, secretory cells (such as those of the adrenal glands), the cells that make up the bones, cartilage, and connective tissues of the head (including the larynx), and neurons of the autonomic nervous system,” the scientists explain. These cells are mysterious and influential—similar to stem cells, but but not quite the same.
Why is the white facial fur a “domestication phenotype”? Well, the neural crest is responsible for melanocytes (cells that bring pigmentation to skin or fur) as well as adrenal secretions—and as the number of neural crest cells goes down, both adrenal secretions and melanocytes are reduced in turn.
In marmosets, scientists believe, reduced adrenal activity is being selected as something that “domesticates” animals for cooperation within their own groups. And the evidence, they say, is as plain as the spot on the marmoset’s face.
Neural crest cells also play a role in vocalization, another trait that reflects domestication. In part of this study, scientists divided a group of baby marmosets and changed the way they received vocal feedback from an artificial parent. “The rate of white patch development was significantly faster for the marmosets that received vocal feedback 100 [percent] versus 10 [percent] of the time,” the researchers explain, “supporting the hypothesis that the amount of parental vocal feedback can indeed change the developmental trajectory of the white facial patch.”
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Humans and monkeys in the marmoset family have something important in common for this study. The scientists explain:
“Humans and most species in the callitrichine subfamily of monkeys (to which marmosets belong) are the only primates to exhibit cooperative breeding in which both parents, older siblings, and unrelated conspecifics help care for infants. In both cases, the energetic costs of caring for one or more infants exceed the capacity of a single parent.”
That’s because both marmosets and humans have altricial babies, from the Latin for needing nourishment—meaning offspring that can’t take care of themselves even a tiny bit at the beginning. Studying marmoset neural crest implications, therefore, could shed new light on human development too.
“This in turn provides new insights into how selection on correlated phenotypes may have acted during human evolution, as hominins became increasingly reliant on cooperative networks for survival and reproduction,” the scientists conclude.
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