Preauricular grooves on Japanese female skeletal remains in Edo as a bioarchaeological indicator in population studies

Preauricular grooves in women are considered as an indicator of childbirth or pregnancy. We examined 522 female pelvises excavated from archaeological sites in Edo (present-day Tokyo), Japan, which underwent population growth during the Edo period (AD 1603–1867). We analyzed the frequency of preauricular grooves by estimated age group, burial period, and type of burial facility in Edo to infer age-related changes and chronological as well as social-rank-related differences during the Edo period. We found that the frequency of preauricular grooves increased with individual age. Moreover, a higher frequency of developed preauricular grooves was observed during and after the 18th century (the middle–late Edo period) compared with those observed in the 17th century (early Edo period) in all age groups. The frequencies of preauricular grooves in remains buried in kamekan (ceramic coffins) and hayaoke (circular wooden coffins) revealed no social differentiation of reproduction rate. These results suggest that the average number of births per woman during and after the 18th century may have exceeded that in the 17th century. Consequently, it is highly probable that the population increase known to occur in Edo during the 17th century was caused by an influx from rural areas rather than by an increasing number of births among the city’s female residents. Furthermore, the number of pregnancies and births did not differ significantly among different social classes during the later Edo period.