Parasites and archaeology
If you try to imagine how different life was for our ancestors from life today, being cold and hungry might top the list. Winter especially must have been hard to bear without heated homes and an adequate supply of appetising and nourishing food. Perhaps the elite members of society did not have to worry about those two issues, but even they could not escape the misery of infection by various parasites, including head lice – to the benefit of archaeology, as we are now discovering, thanks to a paper in the journal Molecular Biology and Evolution (https://doi.org/10.1093/molbev/msab351).
This report says that most ancient humans carried head lice, and their eggs abound in historical hair specimens, providing a rich source of ancient DNA that can be extracted without causing damage to the original materials, unlike DNA sampling from bones and teeth, which involves an element of destruction that is often forbidden for curatorial reasons. This source of DNA can also be used where bones and teeth are not available, because lice eggs can be found as well in textiles that incorporate human hair.
It is not the eggs themselves that yield the vital DNA, but rather the ‘nit glue’, the sticky substance excreted by head lice to attach their eggs to the hair of the host. This is long-lasting and often incorporates fragments of the host’s skin and hair. Samples were found to contain the same concentration of DNA as a tooth, double that of bone remains, and four times that recovered from the human blood ingested by body lice.
To demonstrate the research potential of this finding, the team studied the hair of ancient Argentinian mummies dating from 1,500 to 2,000 years ago. They were able to track the migrations of pre-Columbian peoples of South America, revealing that the original populations of the Andes mountain region of San Juan province, in central west Argentina, migrated from the rainforests of north-west Amazonia, in the area south of current Venezuela and Colombia.
The authors were able to determine the sex of the human hosts, and map some of the founding mitochondrial lineages of the population they were studying. They found evidence of some of the viruses they had suffered from, and concluded that extremely cold temperatures could have been a factor in the deaths of the mummified individuals, because of the very small gap between the nits and scalp on the hair’s shaft – lice rely on the host’s head heat to keep their eggs warm and so lay them closer to the scalp in cold environments.
Dr Alejandra Perotti, Associate Professor in Invertebrate Biology at the University of Reading, who led the research, said ‘head lice have accompanied humans throughout their entire existence, so this new method could open the door to a goldmine of information about our ancestors’.
The delicate subject of paternity
It is a frequent theme of TV detective dramas – the husband who turns murderous when he discovers that his children are not his own – but another study suggests that, before the era of DNA testing, paternity was always difficult to establish: indeed, the principle is enshrined in Roman law that mater semper certa est, pater semper incertus est (‘the mother is always certain, the father is always uncertain’).
Writing in Current Biology (https://doi.org/10.1016/j.cub.2019.09.075), Maarten Larmuseau, of the Catholic University of Leuven, reports on a study of 513 pairs of men living in modern Belgium and the Netherlands who thought they shared a paternal ancestor as far back as the 15th century. If they truly shared the same male ancestor, they would also share a Y chromosome, which is passed down directly and exclusively from father to son. If the men’s Y chromosomes did not match, then somewhere along the line the paternal line had been disrupted.
Larmuseau and his colleagues found that the rate of what they termed ‘social’ fathers as opposed to ‘biological’ fathers was stable at 1% for both Belgium and the Netherlands, and that the religious differences between the Catholic and Protestant parts of the Low Countries seemed not to be an influence on extramarital progeny. Instead, socio-economic factors seemed to account for the major findings: correlating the DNA results with birth registers and other documents, it became clear that births from extramarital couplings were as low as 0.5% among rural populations but as high as 6% among densely populated city-dwellers.
Larmuseau noted that in literature and drama, paternity controversies are presented as ‘a particular affliction of the aristocracy’, whereas the opposite seems to have been the case, the rate being highest among urban labouring classes and lowest among middle- and upper-class country folk. ‘Births outside marriage can be due to affairs, but also rape and sexual aggression’, he said, so it is not possible to tell whether the extramarital births were consensual on the part of the mother. He did, however, warn that people investing in DNA ancestry kits should be aware that they might not get the answers they were expecting: people who want to know if they have Viking DNA or are related to Richard III might instead discover an awkward family secret.
Archaeologists like to find neutral, non-judgemental terms to write up their research when dealing with sensitive topics, so Maarten Larmuseau’s paper refers to ‘extra-pair paternity’ to describe the tell-tale mismatch in Y chromosome that indicates extramarital paternity. In another study, researchers from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and the University of Chicago, USA, investigated how common close parental relatedness was in our ancestors, but tried to avoid using the terms ‘incest’ or ‘inbreeding’.
Instead, the paper published in Nature Communications by Harald Ringbauer et al. concerned with ‘parental relatedness through time’ (https://doi.org/10.1038/s41467-021-25289-w) refers to ‘runs of homozygosity (RoH) in ancient DNA’. In simple terms, RoH, or stretches of DNA with little genetic variation, are more frequent and longer in the offspring of closely related parents. Studying ancient DNA from 1,785 people, dating from 45,000 to a few hundred years ago, the research team found that only 53 (3%) had DNA indicating their parents were first cousins, and just one that was probably the result of brother–sister or parent–offspring incest. The 53 people were randomly distributed through history and geography, rather than concentrated in any one place or time, with the exception of three out of 11 people from Iron Age Republican Rome.
In other words, despite the small size of prehistoric populations, our ancestors only rarely chose their close relatives as mates, and unions between cousins are exceptional, rather than common. However, the research teams also found that many couples were distantly related to each other via ‘deeper connections in their pedigree’, as an almost inevitable consequence of living in small communities. This relatedness fell dramatically in the Neolithic, partly because population numbers grew with the onset of agriculture: it has been suggested in the past that the gatherings associated with causewayed enclosures in the early Neolithic had the effect (whether intended or not) of encouraging animal and human exogamy – breeding or marriage between unrelated individuals.
By contrast, the researchers say, marriage to a first or second cousin has become much more prevalent over time, and now accounts for as much as 10% of all global marriages, hence the headlines that accompanied the publication of this research in the media: that ‘people today are more likely to breed with their cousins than in prehistory’.
An astonishing hoard of 41 gold objects has been found in Brandenburg and their name – Regenbogenschüsselchen, or ‘rainbow cups’ – is as intriguing as their shape. According to Marjanko Pilekic´, a numismatist and research assistant at the Coin Cabinet of the Schloss Friedenstein Gotha Foundation in Germany, the bowl-shaped objects in the hoard are imageless coins, dating from between 125 BC and 30 BC, during the late Iron Age.
In diameter and weight, they are comparable to the staters that began to circulate in Europe in imitation of those of Philip II of Macedonia in the mid-5th century BC. Apparently, they are not uncommon as archaeological finds, and the German name refers to the popular belief that you will find a pot of gold if you could only find the elusive end of a rainbow.