5.1 Sex and age profiles
The sex and age profiles of the sites presented here are statistically divided in intervals of 5 years (Acsádi & Nemeskéri 1970, 62). Normal versus abnormal profiles will be discussed especially for the proportion of immature individuals. The sites and corresponding demographic data are divided in three groups, based on their age and geographic setting, each comprising two sites: 1) the Late Mesolithic sites, dating from c. 5500-4500 BC, namely Hardinxveld-Polderweg and De Bruin in the Dutch river area. 2) Swifterbant and Urk, dating from c. 4200-4000 BC and located in the middle of the Netherlands (the IJsselmeer Basin), and 3) Schipluiden and Ypenburg, both occupied at c. 3500 BC in the western coastal area. The graphs (Figs. 2-4) display the total number of individuals per age interval, as well as the number of adult male and female individuals.
The mortality curve of Hardinxveld-Giessendam is based on 19 people, 3 females, 8 males, 5 adults of unidentified sex and 3 children and subadults up to 20 years. The last group comprises c.15 % of the total population (fig. 6). The mean age at death for the adults was c. 43.5 years (women 43.3 and men 43.6 years). The presence of shed milk teeth shows, that the sites were used by family groups, including women and children. In view of these data one can conclude that these river dunes were inhabited by families and therefore served as a base camp.
At Swifterbant and Urk data on sex and age of a total of 69 individuals were available for the mortality profile. This group of adults consists of 10 men, 14 women and 30 individuals of unknown sex. Children and subadults (N=15) make up c. 22 % of the population (fig. 7). The mean age at death for the adults was c. 38 years (women 39.6 and men 36.3 years). The presence of women and children is consistent with the occupation of these sites by family groups. The total number of individuals at Schipluiden and Ypenburg amounts to 56, with 16 men, 11 women and 6 individuals of unknown sex. The mean age at death here is 38 years (women 33.5 and men c. 41 years). The percentage of children and subadults is, at c. 42.3 % much higher here (fig. 8). It seems that all members of the local group, the children below 5 years of age included, were buried in the Ypenburg cemetery during a certain stage of the occupation of the dune, irrespective of sex and age. Family groups must have occupied both sites, in view of the presence of children, but the number of women in Schipluiden is too low for a natural population. Evidently the small cemetery site on this dune does not reflect all the mortuary practices as the many isolated bones also indicate an above-ground ritual with disposing the dead, which left hardly any archaeologically detectable remains.
The mortality profiles of the various populations are shown in figure 9. The percentages of young children and subadults are much higher for the combined series of Schipluiden and Ypenburg. The profiles of Hardinxveld-Giessendam, Swifterbant and Urk show an unnatural composition in this respect. Several factors could be responsible for this, such as preservation conditions, which can be unfavourable for young children, and an archaeologically elusive treatment of the dead. This restricts a comparison at the level of demographic analyses. The limited demographic data from these sites may, however, serve as a means of typifying the kind of settlement, to establish whether these were occupied by (complete) families or not. The data from Schipluiden and particularly Ypenburg give a fuller picture of the population structure, especially by the formal burials of young children. In terms of the adult-subadult ratio the data from these two sites show the most normal mortality curve with more than 40 % of individuals classified as subadult.