It is amazing the social customs they can theorize based on almost nothing. They extrapolate to the nth degree and often focus on something prurient for the attention. Attention usually means more money.
I don’t know why they waste money on research like this. Neolithic culture and lifestyles were well documented on TV in the 1960’s on the Flinstones Show. Fred Flintstone never mentions member tattooing or piercing. Although Loyal Order of Water Buffaloes had some peculiar practices.