"We cannot really say how long this individual survived," study co-author Lars Fehren-Schmitz, an anthropologist at the University of California, Santa Cruz, told Live Science in an email. But "the burial of this infant suggests that the Nasca treated this individual in death like most other infants."

The skeleton of this female infant was discovered alongside a second one inside a ceramic urn at the archaeological site of Jauranga in Peru's Palpa Valley, where numerous geoglyphs known as the Nazca Lines have been found. Archaeologists uncovered several dozen other burials dated to the Middle Nazca (also spelled Nasca) period (A.D. 325 to 440) at the site, but one of the co-buried infants had an extremely rare condition, researchers wrote in a study published Monday (Nov. 9) in the journal PNAS.

The infant had a very small skull and a single eye socket in the middle of her face, along with other developmental issues of the cranial bones. These traits match modern clinical descriptions of cyclopia, a lethal condition that occurs when the front part of a fetus's brain fails to divide into left and right hemispheres.

This condition can also cause alterations in the nasal structures, resulting in a missing nose or a tube-like nose above the single eye.

"The cause of the malformation was present at fertilization, but manifestation occurs around the fourth to fifth week in utero [in the womb], when the frontal lobe of the brain has to divide," study first author Elsa Tomasto-Cagigao, an archaeologist at the Pontifical Catholic University of Peru, told Live Science in an email.

Cyclopia is a rare condition, occurring in about 1 out of every 100,000 births. To learn more about the infant's short life, the researchers sequenced her genome. (DNA suggested the infant carried two X chromosomes, typical of a female.)

The team detected an extra copy of chromosome 13, meaning the infant had a genetic condition called trisomy 13, or Patau syndrome. It's known to be a major chromosomal cause of cyclopia; that said, only a small percentage of trisomy 13 cases involve cyclopia.

While trisomy 13 is associated with advanced maternal age, it is not clear whether that was the case for this infant, Fehren-Schmitz said.

"This condition has been documented in historic and modern anatomical collections, but to my knowledge this is the first archaeological example of this developmental abnormality," Siân Halcrow, a bioarchaeologist at the University of Otago in New Zealand who was not involved in the study, told Live Science in an email.

The researchers' estimate of the infant's age at death suggests she may have survived for several weeks or months after birth, Halcrow pointed out. "This raises important questions about how infants with profound congenital differences were cared for and treated in past societies," she said.

The infant was buried in a ceramic urn, the researchers noted in the study, which was a common burial method in the Nazca period, along with a second female infant who had no skeletal abnormalities. "The baby with cyclopia was at the bottom of the jar, while the other baby was on top. Nevertheless, it appears that they were interred in a single event," Tomasto-Cagigao said. The genetic analysis showed that the two infants did not have the same mother.

A burial of two infants in one urn is unusual for this culture, the researchers said, but there is not enough archaeological evidence to conclude that the infant with cyclopia was given a different type of burial.

"The fact that the individual was buried with a 'healthy' individual in a regular cemetery, without any special grave goods, suggests that, to some extent, the individual was not treated differently in death, even though it had such a rare condition," Fehren-Schmitz said. "It was neither 'excluded' because of it nor treated in a 'special' way."

In ancient Andean societies, some people with disabilities took on special societal roles, such as ones associated with religious practices. "If that reflects Nasca society as a whole, we can't say based on one case," Fehren-Schmitz said, "but it does reflect the community this infant was part of, even if only briefly."

'> Nazca infant had rare, fatal birth defect that left her with one central eye 1,600 years ago El Niño, a periodic weather phenomenon that can lead to intense rains and flooding in Peru and droughts in other parts of South and Central America.

"We have one example at the site of Sicán where around [A.D.] 1050/1100, around 200 individuals were killed and ritualistically buried during an intense El Niño event," study co-author Haagen Klaus, an anthropology professor at George Mason University in Virginia, told Live Science in an email.

Other human sacrifice findings include more than 200 children found near the modern-day town of Huanchaco who were sacrificed sometime between 600 and 800 years ago, possibly during an El Niño.

However, despite the occurrence of human sacrifice, levels of violence unrelated to sacrifice were actually quite low in the Lambayeque Valley. In the study, scientists analyzed the skeletal remains of 1,519 people from the Lambayeque Valley who lived between roughly 1500 B.C. and A.D. 1800, and whose remains were preserved enough to detect signs of violent trauma, including interpersonal violence.

Of these skeletons, "only 25 (1.6%) exhibited traumatic lesions consistent with interpersonal conflict, and 77 exhibited post-cranial traumatic lesions consistent with accidental trauma (5.1%)," Klaus and co-author Thomas Snyder, a bioarchaeologist at New York University, wrote in the paper, which was published Nov. 8 in the journal Frontiers in Environmental Archaeology.

The team didn't find any link between a person's sex and violence, they noted. The findings mean that despite the presence of human sacrifice, the amount of violence unrelated to sacrifice was low. This leaves a question: Why?

"Ritual violence may have alleviated non-ritual violence by creating spaces where social tensions could get worked out in a few different ways," Klaus said.

It's important to remember that other areas of Peru also practiced human sacrifice but didn't have the same low levels of interpersonal violence. Klaus noted that areas in the Peruvian highlands sometimes had higher rates of interpersonal violence. In their paper, Klaus and Snyder noted that societies that originated in the highlands, such as the Tiwanaku, Wari and Inca had to grapple with poorer soils and cold temperatures, and these challenges may have been a factor in increasing the levels of interpersonal violence.

The "evidence of sub-lethal and lethal violence forceful enough to break bone is significantly higher in some areas of Peru's highlands," Klaus said. He and Snyder noted in their paper that the inhabitants of the Lambayeque Valley may have had better access to marine and water resources, such as seafood and rivers that could be used for agricultural irrigation, than those who lived in highland areas. Access to these resources may have helped alleviate interpersonal violence in the valley by providing more food resources, they wrote.

Scholars react

Aside from practicing human sacrifice, people in the valley may have engaged in other practices that helped lower levels of interpersonal violence, researchers who were not involved in the new study told Live Science.

Environmental conditions may have helped reduce conflict or there could be "really unusual cultural practices in this region of avoiding or mediating conflict — both between and within groups," Elizabeth Arkush, an anthropology professor at the University of Pittsburgh, said in an email.

Constanza Ceruti, an anthropologist and explorer with the National Geographic Society, said in an email that she's glad that researchers are studying human sacrifices "after decades of being ignored as a taboo topic in academic discussion." She praised the study’s large sample size and noted that human sacrifice is a "phenomenon primarily associated [with] the manipulation and concentration of power by elites."

Jordi Rivera Prince, an anthropology professor at Tulane University, said that the findings dovetail with her excavations in the region, where she has "found little evidence of violent trauma during the Salinar (400-200 BCE), a period of great social change in the Andes."

Weston McCool, an archaeology professor at Cal Poly, said in an email that the newly published paper "is an interesting study that provides additional evidence for a sharp break in patterns of violence between the Andean coast and highlands." He noted that it "supports the hypothesis that coastal populations were buffered from terrestrial environmental downturns in ways that highland populations were not. The nature of that resilience, however, remains an important question for future research."

'> Did human sacrifice help lower violence? New research in Peru leaves intriguing question