Here’s what you’ll learn when you read this story:

• Although chickens and mice look nothing alike, they share the same genetic blueprint for buildings faces. So, what creates facial variety?
• A new study finds that signal sites (known as “developmental organizers”) and the mesenchymal cells receiving those signals differentiate among species, rather than altering the baseline genetics.
• Scientists also discovered that many of these elements overlapped with genomic regions associated with human facial traits, which explains the wide variability within our species.

With more than eight billion humans on the planet, the species Homo sapiens alone contains a dizzying number of facial variations. But incredibly, evolution uses the same developmental programs to develop faces across species as well. So, how exactly does nature create such widespread variation—both within one species and across many separated by hundreds of millions of years of evolution?

A team of scientists—hailing from the Max Planck Institute for Evolutionary Biology in Plön, Germany, and the Lawrence Berkeley National Laboratory in California—performed single-cell transcriptomic profiling of chickens and mice to discern exactly how facial variation is constructed. During embryonic development, signal hubs known as “developmental organizers” act like foremen on a construction site. They tell nearby cells what to grow or become, and during facial construction, one of these “foremen” is located in the ectoderm, the outermost layer of the embryonic cell. From this site, it sends out molecules known as morphogens that govern tissue development and are remarkably similar across species.

So, why do the resulting faces look so different? It’s all about the regulators—specifically, non-coding DNA sequences that act as switches, determining what particular genes are expressed. The results of the study were published in the journal Science Advances.

“During embryonic development, many genes are used repeatedly in different tissues and at multiple stages,” Markéta Kaucká, the senior author of the study from Max Planck, said in a press statement. “If you change the gene itself, you risk breaking many processes and body parts at once. But by modifying the regulatory elements that control where and when the gene is used, evolution can reshape specific features, such as the face, without compromising the whole organism.”

However, these signal hubs are only part of the variation equation. Mesenchymal cells—multipotent stem cells that differentiate into various bone, cartilage, fat, and muscle—also receive signals from these organizers in differing ways among species. “Facial diversity is not only shaped by changes in how signals are produced, but also by how they are perceived by other cells,” Stella Kyomen, a Ph.D. student at Max Planck and the first author of the study, said in a press statement.

None of this explains the wide facial differences in our species, but researchers found that the tools evolution uses to differentiate facial structure across a broad genetic blueprint also plays a varying role within a species. Many of the regulatory elements that play a role in developing the face overlapped with genomic regions related to human facial traits.

In other words, Mother Nature is the true progenitor of the long-held maxim: “Work smarter, not harder.”