DNA analysis of a grave from the Upper Palaeolithic containing the remains of two newborn babies has revealed that they were identical twins. The discovery marks the earliest known example of monozygotic twins confirmed by analysis of their ancient DNA. Uncovered at the Gravettian site of Krems-Wachtberg in Austria, the twins were buried next to a 3-month old infant who was a third-degree male relative, possibly a first cousin.

Immature human remains from the Upper Palaeolithic are extremely rare, so to find three that reveal new insights into the funerary practices of early humans is a unique and significant discovery. The findings were published in the journal Communications Biology.

The town of Krems in Austria was home to traveling groups of hunter-gatherers around 40,000 to 30,000 years ago. What’s known about their lives and lifestyle is lifted from thick loess sediments, which over the centuries have been blown in by the wind burying the clues left behind by our ancestors. The site at Krems-Wachtberg where the three ancient graves were found is an exceptional one for yielding information as organic materials have been particularly well preserved in the sediment.

Key features found 5 meters (16.4 feet) beneath the site included a large hearth with connected pits, infant burials, and artifacts including art objects and personal adornments that attribute the settlement to the Pavlovian culture, a variant in the earlier Gravettian. The archaeological teams used radiocarbon dating to confirm the estimation, but the conclusion of the site being a Gravettian/Pavlovian settlement is also supported by the mortuary practices seen in the infant burials.

The first grave was oval-shaped and contained the remains of two infants, each embedded in red ochre and placed next to each other facing east with their skulls pointing north. The bodies were laid to rest with 53 beads made of mammoth ivory, the arrangement of which indicated they had been threaded on a string. The beads were uniform in size and showed no signs of wear, which means they were crafted as an offering for the deceased.

After the infants had been placed in the grave, it wasn’t filled with soil but instead sealed off using the shoulder blade of a mammoth that revealed signs of being chipped into shape using a tool. This method of burial meant the bodies were well-preserved allowing the researchers to do a DNA analysis using the newborns' teeth. Their results revealed that the twins were full-term newborns, marking the earliest known example of monozygotic twins as their DNA was identical. One of the newborns died at birth while the other survived for approximately 50 days before joining their sibling. The findings, while tragic, are a fascinating insight into the mortuary behaviors of the Gravettian as it demonstrates the decision to reopen a grave and manipulate its contents to make room for the second twin.

Monozygotic twins, also known as identical twins, form in the womb when a single fertilized egg splits into two separate embryos. It gives rise to two (or more) offspring with identical genotypes and phenotypes, meaning they look and are genetically the same. The same process of a single egg splitting can result in conjoined twins, except in these cases the egg fails to fully separate, which is why the two individuals are connected. Dizygotic twins occur when two eggs become fertilized in the same pregnancy, which is why some twins are different sexes.

A third infant was also found in a second longer and narrower grave pit at the site. This grave was also found to contain evidence of adornments for the corpse, including a suspected clock pin made of mammoth ivory. This grave was backfilled with soil instead of being sealed with a protective plate, which meant the body was poorly preserved compared to the twins in the oval grave.