Convergence (also known as evolutionary convergence) is a term used in genetic genealogy to describe the process whereby two different haplotypes mutate over time to become identical or near identical resulting in an accidental or coincidental match. Coincidental matches can sometimes be in different subclades and the common ancestor will have lived several thousand years ago rather than within a genealogical timeframe. One might think of convergence as producing "false positive" matches. One would ordinarily interpret a match as indicating a common ancestor but if convergence - rather than inheritance - is operating, there may be no common ancestor. The match is positive but false.
Convergence is likely to be a particular problem within haplogroups R1b and I1 which both have a more recent origin but expanded very rapidly. The haplotypes which are most affected are likely to be those which are closest to the modal haplotype for the haplogroup, such as people who match the Western Atlantic Modal Haplotype. The presence of matches with a large number of different surnames is a possible indicator that convergence has occurred. Convergence is more likely to be a problem with low-resolution 12-marker and 25-marker matches, but does also occur with 37-marker matches. It is less likely to occur at 67 markers, though a case has been reported of two 67-marker haplotypes with a genetic distance of 6, which were found to be in different R1b subclades. If convergence is a possibility then it is recommended to upgrade to a minimum of 67 markers and to order SNP testing to help rule out the coincidental matches which will have no genealogical relevance.
The incidence of convergence is not known, largely because the majority of people in the FTDNA database have not ordered any SNP testing. Robert Casey has estimated that perhaps only 5% to 10% of surname clusters are affected by the problems of convergence but for the people in such clusters perhaps 20% to 90% of their matches might be false positives.
- Larmuseau MHD, Vanderheyden N. Van Geystelen et al. Recent radiation within Y-chromosomal haplogroup R-M269 resulted in high Y-STR haplotype resemblance. Annals of Human Genetics 2014; 78 (2): 92-103.
- Chuan-Chao Wang, Ling-Xiang Wang, Rukesh Shrestha, Shaoqing Wen, Manfei Zhang, Xinzhu Tong, Li Jin, Hui Li. Convergence of Y chromosome STR haplotypes from different SNP haplogroups compromises accuracy of haplogroup prediction. Paper submitted to pre-print Arxiv server on 21 October 2013.
- Common haplotypes by Georgia Kinney Bopp
- Example of Y-STR convergence A diagram compiled by Mike Walsh showing a hypothetical example of convergence in R1b-P312 and R1b-U106.
- DNA convergence and Chicken Little by Mike Maglio. Origin Hunters, 5 December 2014. See also the related discussion on this issue in the ISOGG Facebook group.
- Smolenyak M and Turner A. Trace Your Roots with DNA. Rodale, 2004, p251.
- Mayka L. Coincidental convergence (or lack of divergence). Posting on the Rootsweb Genealogy DNA mailing list, 5 November 2012.
- Casey R. YSNPs - key to the future. YouTube presentation, 30 October 2013.