HapFABIA found 160,588 different very short IBD segments on chromosome 1. These contained 751,592 rare variants, which amounts to 39% of the rare variants and 23.5% of all SNVs. The distance between IBD segments had a median of 653 bp and a mean of 1.55 kbp and ranged from 0 (overlapping IBD segments) to several Mbp. The number of tagSNVs for an IBD segment ranged from 9 to 266, with a median of 11 and a mean of 15.5. The number of chromosomes that shared the same IBD segment was between 2 and 185, with a median of 6 and a mean of 13.5. The length of IBD segments ranged from 34 base pairs to 21 Mbp, with a median of 23 kbp and a mean of 24 kbp. IBD lengths are computed as described in Section 4.1, to match the assumptions for the distribution of IBD segment lengths as derived in other publications (17,16,19,18). A 20 kbp long IBD segment corresponds to a common ancestor 50 kya (see Section 4.1.1, for the relation between IBD segment length and years from present). Therefore, the median length of 23 kbp of IBD segments corresponds to 43.5 kya. That rare SNVs can be old is supported by a recent publication (20) which reports that the average origin of SNVs is 34.2 kya in Europeans and 47.6 kya in Africans, while the SNVs shared between European Americans and African Americans date back 104.4 kya and 115.8 kya, respectively.