Surnames in Sardinia. III. The spatial distribution of surnames for testing neutrality of genes.

1. A study on heterogeneity of males' surnames over time and space in the island of Sardinia was carried out using data from consanguineous marriages (1800-1970) and telephone directories (1978). 2. Variation of frequency of surnames over time is barely significant and 10 times lower than that over space, which is very highly significant. 3. For sufficiently frequent surnames the estimate of the Wahlund variance, calculated from chi 2 for heterogeneity in space, is independent of the frequency of a surname: this supplies evidence of neutrality in line with that obtained from the frequency distribution of surnames. 4. The Wahlund variance, W (also called FST), decreases regularly as the average size of the area considered (number of individuals per area, N) increases. The estimate of the parameter beta in the relation W = KN beta could be of interest for the study of population structure. 5. A correction factor of 1/4 must be made on the surnames' variance in consideration of their haploid unisexual transmission. 6. It is suggested that surnames could provide a baseline for estimating the value of Wahlund variance under random genetic drift and hence evaluating whether a gene behaves as selectively neutral. 7. The distribution of the Wahlund variances obtained from two sets of gene frequency data as compared with that obtained in comparable conditions for surnames in the same areas seems to show that most genes behave as neutral, with the exception of a few, with high W values, which presumably have been under different selection pressures in the area examined.