Reacción a "Reactions to study finding remains of foetuses and babies with Down's and Edwards' syndromes thousands of years old"

From my perspective, the most remarkable innovation of this study lies not so much in the technical aspect (without detracting from the enormous computational effort and challenge), but in its conceptual approach. The idea of analysing a significant number of genomes from ancient remains, almost 10,000 in total, to investigate the prevalence of certain biomedical conditions in past societies is revealing. Furthermore, the integration of this information with anthropological and archaeological data provides a solid basis for hypothesising how these societies dealt with human diversity, especially in relation to well-known conditions such as Down syndrome and Edwards' syndrome. 

The authors approach the study with outstanding technical skill and construct a cautious and self-critical account that reveals some limitations. Despite the presence of certain weaknesses, the study opens a significant window that will spark interest in further investigating other conditions and diseases with very low prevalences, which until now could not be addressed due to the limited population data available for ancient DNA. 

Very briefly, the study argues that:  

• The prevalence of trisomies does not appear to be significantly different from that observed in current populations. There is an insignificant deviation that could be due to sampling phenomena, preservation of skeletal remains, etc. 
• Through the analysis of burial rituals, the authors suggest that ancient societies did not distinguish between individuals with these syndromes and other members of the population. 

The most significant impact of this study lies in opening a new avenue of exploration of our past, highlighting the importance of integrating information from diverse fields of knowledge, from genetics to physical anthropology. 

In my opinion, there are some weaknesses in the results of the study that are not sufficiently addressed. The question of prevalence is somewhat ambiguous. Although the overall prevalence of trisomy 21 (Down syndrome) is slightly lower than expected internationally (considering a correction for maternal age), it is striking that three of the six cases are concentrated in two nearby sites in Navarra (Spain) that correspond to the Early/Middle Iron Age (800 to 400 BC), generating an abnormally high (unreported) prevalence at the national level. The only detected case of Edwards syndrome is also recorded in this region. On the other hand, the presence of infant burials in the archaeological record is scarcer than adult burials, so the prevalence of these syndrome cases in the context of infant burials could be abnormally high in the data set studied, significantly altering the overall and national prevalence estimate.   

I always consider it good practice to develop discussions not only with what one finds, but also with what one does not observe in the record. This comment is relevant because all the cases detected are perinatal (or neonatal; the use of neonatal/perinatal is ambiguous) and only one infant is identified. It is curious that older individuals, or simply more infants, do not appear, given that the average life expectancy of people with Down syndrome should favour their more frequent presence in the archaeological record. The absence of such cases in burials could lead us to rethink whether ancient societies treated diversity equitably, which would call into question one of the fundamental conclusions of the paper. 

The most obvious limitation, from my perspective, lies in the need to interpret society's perception of people affected by syndromes based on how they were buried. The burial ritual could provide only a partial perspective on the story. In addition, since all identified cases correspond to early age stages (perinates/neonates/infants), there is a possibility that these individuals had not yet developed distinctive features. This could lead to a homogeneous treatment in the burial ritual due to the lack of identification of these traits. 

In time, it will undoubtedly be possible to deepen these studies and validate the results of the research. For now, this initial proposal is extremely attractive, opening a new window into our past (where do we come from?), always crucial to become aware of ourselves (who are we?) and to understand the human condition in a future social context (where are we going?).