The silvery fur of the hamadryas baboon is, under a spectrometer, nearly the exact color of moonlight, which may explain why ancient Egyptians made a monkey the face of their moon god, according to a new study in Time and Mind.
The work, from biological anthropologist Nathaniel Dominy of Dartmouth College and primatologist Catherine Hobaiter of the University of St Andrews, takes an old Egyptological question and points an instrument at it. Thoth, god of the moon, writing, and magic, had two sacred animals: the ibis and the baboon. The ibis makes sense. A curved beak echoing a crescent, white plumage the same color as the moon’s glow.
The baboon, however, has long “defied explanation,” as one Egyptologist put it; the key problem being that baboons didn’t live in Egypt.
Egypt’s pantheon features many local creatures, from the jackals that haunted its cemeteries to the cow that stood in for the mother goddess Hathor. But no wild baboon has ever been found in Holocene Egypt. The hundreds recovered from tombs and temples were all imports, carried in by ship from somewhere down the Red Sea coast. Of all the animal gods, the baboon is the only foreigner.
“Why would two such different animals be used to represent one deity? Most other Egyptian deities are represented by just one type of animal. Ancient Egyptians were familiar with at least three species of ibis, but they chose the white one for embodying Thoth. They were also familiar with two species of baboon, along with vervet monkeys and patas monkeys, but again they chose the silver-white species,” explained lead author Professor Catherine Hobaiter in a press statement.
According to the study, the Egyptians were picky. They knew two species of baboon and three of ibis, and each time they deified only one of each.
“Sacred ibises and hamadryas baboons are different in many ways, but one thing that unites them is their moon-like colour,” Hobaiter said.
To test whether color was the thread, the team recorded reflectance spectra from the hair of 12 baboon specimens at the American Museum of Natural History and lined them up against the measured spectrum of moonlight. The olive baboon came back green, peaking around 525 to 650 nanometers (which is precisely why it is called the olive baboon). The hamadryas came back silver-gray, roughly 65 percent brighter, with a curve the authors call “indistinguishable from moonlight.”
According to the study and historical records, the living emblem of Thoth is not just the hamadryas but the mature male, with his heavy silver shoulder mantle and white cheek ruffs. This head of hair is so reflective the authors clock it as brighter than a golden lion tamarin, a monkey practically famous for glowing. The Germans noticed too. Their name for the animal is Silberpavian, the silver baboon.
There is a stranger layer beneath the color. Egyptians kept baboons in their temples partly to watch them, because the animals seemed to answer to the moon. There are historical records which indicate that male baboons in Egypt, during a fifth-century solar eclipse, fell into a state of “grief” and, according to the ancient writer, entered a sort of trance of reverence.
Modern ethologists watching zoo baboons during the 2017 total eclipse logged something uncomfortably close: activity falling away, the animals going quiet and huddling together. The Egyptians, in effect, may have kept a small colony of living eclipse detectors and read their unease as devotion.
History being what it is, and not an exact science, the authors are careful not to pretend that their findings are direct evidence as to why Ancient Egyptians made gods of baboons. A spectrometer can confirm that a baboon is the color of moonlight. It cannot confirm that the color is why anyone bowed to it. The argument rests on a 2024 etymology tracing Thoth’s name to a word meaning roughly “bright-thing.”
There is also an irony the study mostly steps around. The male’s silver mantle did not evolve to look like the moon; it evolved as a sexual signal, a way for dominant males to advertise themselves to other baboons. The Egyptians took a mating ornament and read it as a message from the sky.
That may be the most human thing in the whole account. The Egyptians were meticulous observers who noticed that one animal, in one sex, at one particular brightness, resembled the thing they worshiped, and decided the resemblance meant something.
One of those baboons even has a name. Harnufi was brought to Egypt in the sixth year of Ptolemy V and entombed 31 years later, on September 6, 168 BC. Someone counted out his life in years, mummified him, and laid him down as a small gray piece of the moon.
MJ Banias is a co-founder of The Debrief, covering science and technology news. You can email him at mj@thedebrief.org or follow him on LinkedIn.