The members of R1b are believed to be the descendants of the first modern humans who entered Europe about 35,000-40,000 years ago ( Aurignacian culture). Those R1b forebearers were the people who painted the beautiful art in the caves in Spain and France. They were the contemporaries (and perhaps exterminators) of the European Neanderthals.

R1b is the most common Y haplogroup in Europe - more than half of men of European descent belong to R1b. Fourteen of the 30 most common haplotypes in the YSTR.org database are typical of R1b. (Those haplotypes can be seen here). The haplogroup R1b is defined by an SNP called P25. It has been found that all European R1b's have an additional mutation called M269. Therefore the 2003 version of the YCC nomenclature named the group defined by M269 as R1b3. However this group is still often referred to as R1b to avoid confusion between the 2002 and 2003 nomenclatures.

Since the majority of men of European descent belong to R1b, this group has the highest risk of so called "accidental" matches - matches due to an accidental convergence of long separated R1b lines, rather than due to recent kinship. Most different surname matches among R1b's are probably of this variety. In general, the closer a haplotype is to the R1b modal haplotype, the more of these accidental matches that will be seen. You can read more about accidental matches here.

While several R1b sub-groups have been found, it turns out that they are only seen in very small percentages of R1b's. The majority of men in R1b belong to none of the known sub-groups and are therefore most properly classified as R1b* (or R1b3* in the 2003 YCC nomenclature). However the R1b*s can be divided into two large identifiable groups by the results of a RFLP test of the 49a,f Taq/I locus. The R1b*'s in Western Europe mostly have 49a,f Taq/I results that are categorized as ht15. The R1b*'s seen in Turkey, and Iraq have a different 49a,f Taq/I haplotype known as ht35. Al-Zahery et al in their paper on Iraq theorize that ht35 is actually the ancestral haplotype for R1b3*s. Cinnioglu et al speculate that the ht35 R1b*s may have spent the Last Glacial Maximum in an Asia Minor refugium while the ht15 R1b*s were in an Iberian refugium.

The allele frequency graphs below show that the STRs for the two 49a,f Taq/I haplotypes are nearly identical. The main differences are the alleles at DYS393 and DYS461. Considering that these two lines of R1b*s have been separated for more than 15,000 years it is remarkable how little drift has occurred between their modal haplotypes.

Weale's paper on Armenian Y chromosomes shows many HG1 haplotypes with DYS393=12 - so it can be guessed that many of these R1b*'s may have been ht35.

A comparison between the allele frequencies for R1b* and two of the Basque sub-groups of R1b can be seen here.

The distribution of R1b* in Europe can be seen as the group colored in green on the map on the second page of Semino's paper on European Y chromosomes.