Europe is dotted with great stone monuments built thousands of years ago. Besides the eternal question of why people worked so hard to construct them, anthropologists have debated whether the idea spread from a single region, or evolved independently several times. Perhaps we will never know with complete certainty, but evidence suggests megalith building began in western France, and became an early meme.

People have been aware of local megaliths since they were built, but systematic comparisons of similarities and differences only began in the 19th century. At the time, the preferred theory was that megalith construction didn’t begin in Europe at all, but in the Middle East. The majority of the 35,000 known megaliths lie near coasts so the idea went that the practice spread along the Mediterranean and then Atlantic sea routes.

However, many human practices initially thought to have been invented just once are now known to have started independently multiple times; since the 1970s megalith construction has been tentatively added to this list. Dr Bettina Schulz Paulsson of the University of Gothenburg has analysed dates for megalith construction to conclude the single origin theory was right, but the proposed source very wrong.

In the Proceedings of the National Academy of Sciences Paulsson reports on radiocarbon dating, usually of charcoal, from 2,410 European Neolithic sites, including both megaliths and other sorts of human habitation.

The first megaliths, according to Paulsson, were “closed small structures or dolments built above ground with stone-slabs and covered by a round or long mound of Earth or stone.” Although later megaliths were often sets of standing stones marking astronomical events, the first, beginning almost 7,000 years ago, all appear to have been built over graves.

Within 2-300 years megaliths appeared across western France, Catalonia, Corsica, Sardinia, and even the Channel Islands. Undated graves of similar style have been found in other parts of Spain and northern Italy. On the other hand, somewhat older enormous grave structures near Paris lack megalithic chambers, shedding light on the practice’s evolution.

It is unlikely so many places, all accessible by sea from the oldest megalith sites, would have come up with the same idea independently and almost simultaneously. Therefore, Paulsson proposes, neoliths evolved from previous grave structures in northern France, and the idea spread rapidly. For some reason megalith’s geographic expansion stalled for centuries, before subsequently reaching Great Britain, Portugal, and additional parts of Spain and France. A third wave took the practice to Scandinavia. Only much later did people who were used to placing large stones over their dead come to use the technology for other things.

Whether there is any connection between the European megaliths and somewhat similar, but even older, stones in the western Sahara, remains unknown.